Effects of lifestyle changes and metformin on salt sensitivity and nitric oxide metabolism in obese salt-sensitive Hispanics.

Salt sensitivity is associated with obesity, and increased cardiovascular morbidity and mortality. We investigated whether treatment of obesity and its associated metabolic abnormalities corrects salt sensitivity and restores impaired nitric oxide (NO) metabolism characteristic of salt sensitivity. Twenty, otherwise, healthy obese salt-sensitive subjects completed a 12-month program of caloric restriction, aerobic exercise and metformin. Two salt sensitivity tests were performed, that is at baseline and end of program. Lifestyle-metformin treatment decreased weight (9.8+/-0.3 kg), body mass index (3.9+/-0.2 kg/m(2)), waist (11.5+/-0.5 cm), systolic blood pressure (SBP) (8.6+/-0.4 mm Hg), diastolic blood pressure (DBP) (5.5+/-0.4 mm Hg), triglyceride (40+/-5 mg/dl), fasting (8.3+/-1 microIU/ml) and post-load (20+/-4 microIU/ml) insulin levels, and salt sensitivity. Going from a high-sodium ( approximately 300 mmol) to a low-sodium diet ( approximately 30 mmol of sodium/day) lowered SBP/DBP by 14.7+/-1.7/7.4+/-0.9 mm Hg at baseline and by 8.6+/-1.9/3.2+/-1.2 mm Hg after treatment (P<0.001). More importantly, blood pressure (BP) sensitivity to customary levels of dietary salt ( approximately 150 mmol of sodium/day) was abolished by the lifestyle-metformin treatment. Differences in SBP/DBP between usual and low salt averaged 11+/-1/8+/-1 mm Hg before treatment, and 3+/-1/1+/-0.5 mm Hg after treatment (P<0.001). At baseline, NO-metabolite excretion was inhibited during high salt; this impairment was corrected by the lifestyle-metformin treatment. In conclusion, acquired correctable factors play an important role in the pathogenesis of salt sensitivity associated with obesity. Correction of salt sensitivity may account for the BP lowering induced by weight reduction. Restoration of the inability to increase or sustain NO production in response to high salt could account for the correction of salt sensitivity induced by the lifestyle-metformin treatment.

Increased blood pressure reactivity to dietary salt in patients with the metabolic syndrome.

The metabolic syndrome is a predictor of type II diabetes mellitus and cardiovascular disease. The mechanisms of the increased blood pressure (BP) in patients with the metabolic syndrome are poorly understood. We investigated if salt-sensitivity is a characteristic of the metabolic syndrome. A total of 301 subjects (87 male subjects, 214 female subjects) of 41.5+/-0.7 years of age completed a salt sensitivity test, and were evaluated for the presence of metabolic syndrome. BP and 24-h sodium excretion were obtained under usual, high- and low-salt intakes. BP reactivity to salt was markedly increased in subjects with the metabolic syndrome; its magnitude was directly related to the severity of the syndrome. Reducing dietary salt from the average usual intake (8.2 g/day) to nearly 2.3 g/day lowered systolic blood pressure (SBP) by 8.7+/-1.3 mm Hg in subjects with four and five traits, 6.0+/-1.1 in those with three traits and failed to modify the BP of subjects with one or no traits of the syndrome (P < 0.0001). Salt restriction reduced the percentage of subjects with metabolic syndrome that were hypertensive (8.2 g/day of salt) from 23.8 to 8.2% (chi2: 23.6; P<0.0001). BP of non-hypertensive subjects with metabolic syndrome was also significantly reduced by salt restriction (7.1+/-1.5 and 4.2+/-1.1 mm Hg in those with four or five traits and three traits, respectively). In conclusion, the metabolic syndrome is a strong clinical predictor of salt sensitivity. The enhanced BP reactivity to dietary salt observed in subjects with the metabolic syndrome, may determine the increased BP levels commonly associated with the syndrome.

NAD(P)H oxidase p22phox gene C242T polymorphism, nitric oxide production, salt sensitivity and cardiovascular risk factors in Hispanics.

Mutations in the NAD(P)H oxidase gene may be associated with abnormal superoxide generation, nitric oxide (NO) availability and cardiovascular diseases. We investigated the prevalence of the NAD(P)H oxidase p22phox gene C242T polymorphism, and its possible association with blood pressure, NO production, salt sensitivity and cardiovascular risk factors in Hispanics. Genotype frequencies were as follows: CC, 52.9%; CT, 40.3%; and TT, 6.8%. There were no significant differences in systolic blood pressure, diastolic blood pressure, age, weight, fasting and post-load glucose levels, LDL and HDL cholesterol, triglyceride and urinary albumin levels in subjects with CC, CT or the TT genotypes. Presence of the T allele was associated with increased salt sensitivity in women, but not in men. NO metabolite excretion was markedly decreased both in women and men with the TT genotype (CC: 868+/-79 micromol/day; CT: 839+/-75 micromol/day; TT: 534+/-78 micromol/day; P<0.05). In conclusion, the prevalence of the NAD(P)H oxidase p22phox gene C242T polymorphism in Venezuelans was comparable to that of Caucasians, but different from that of Chinese and Japanese. Although the T allele was not associated with cardiovascular risk factors, hyperinsulinaemia or hypertension, in women, it appeared to be a genetic susceptibility factor for salt sensitivity. Both in women and men, the p22phox gene may play a role in the genetic control of NO levels.

Endothelial nitric oxide synthase polymorphism, nitric oxide production, salt sensitivity and cardiovascular risk factors in Hispanics.

Mutations in the endothelial nitric oxide synthase (eNOS) gene may be associated with abnormal nitric oxide (NO) production and cardiovascular diseases. In this study, we investigated the prevalence of two eNOS polymorphisms, the Glu298Asp variant on exon 7, and the 4a/b variable number of tandem repeats (VNTR) on intron 4, and their association with blood pressure (BP), NO production, salt sensitivity and cardiovascular risk factors in healthy Venezuelans. The prevalence of both polymorphisms in Venezuelans was comparable to that described for Caucasians, but significantly different from that known for African-Americans and Japanese. The 4a/b genotype was associated with reduced levels of NO metabolites (25% decrease), larger BP lowering in response to salt restriction (9.0 vs 4.8 mmHg, P<0.05), greater prevalence of salt sensitivity (39% in 4a/b and 27% in 4b/b; P<0.05) and with higher LDL-cholesterol levels. The Glu298T polymorphism did not affect NO production, nor it was associated with salt sensitivity. Glu298Asp polymorphism was positively associated with higher weight, triglycerides and LDL-cholesterol. Neither polymorphism was associated with changes in fasting or postload serum glucose, BP, obesity and albuminuria. In conclusion, the prevalence of eNOS polymorphisms is strongly determined by ethnic factors. The 4a/b gene polymorphism could be a genetic susceptibility factor for the BP response to salt intake and for the genetic control of NO production. The reduced NO production in subjects with the 4a/b genotype may be responsible for the increased sensitivity of their BP to salt.

Insulin resistance and upper-normal glucose levels in hypertension: a review.

Reduced insulin-mediated glucose disposal, indicative of insulin resistance, has been demonstrated in lean male hypertensives both with the hyperinsulinaemic euglycaemic clamp and the insulin suppression test. In lean hypertensives, insulin resistance was not accompanied by increases in fasting plasma insulin and glucose levels; but with modest hyperglycaemia and hyperinsulinaemia after a glucose load. Population studies (no stratification) reveal that: (1) insulin sensitivities vary widely in normotensives and hypertensives, (2) there are hypertensives and normotensives with similar degrees of insulin resistance, (3) not all hypertensives are insulin resistant, and (4) insulin resistance does not contribute to the blood pressure level of the hypertensive population. In large cross-sectional studies, the clustering of obesity, dyslipidaemia and type 2 diabetes is largely responsible for the observed associations between insulin or insulin resistance and hypertension. Recent studies indicate a role of glucose in blood pressure control. Glucose has been shown to elevate blood pressure in the presence of endothelial dysfunction and glucose values in the upper-normal range have been shown to be associated with increased cardiovascular mortality. Since endothelial dysfunction is present in hypertensives, dyslipidaemic, obese and in glucose intolerant individuals, lowering of high-normal glucose levels becomes a new, additional therapeutic target in the management of these patients. Hyperglycaemia together with endothelial dysfunction may account for the increased incidence of hypertension in obesity and diabetes mellitus. Because of the strong association between insulin resistance, hyperglycaemia and endothelial dysfunction, and the clustering of risk factors in these subjects, we propose the lowering of high normal glucose levels as part of the therapeutic strategy to prevent cardiovascular and metabolic disease.

Differential blood pressure effects of oral glucose and intravenous L-arginine in healthy lean normotensive and obese hypertensive subjects.

We investigated the role of insulin and glucose in the pathophysiology of hypertension associated with obesity. The comparative effects of an oral glucose load and of an L-arginine infusion on plasma glucose, plasma insulin and blood pressures (BP) were assessed in lean normotensive and in obese hypertensive males. Oral glucose (75 g in 1-2 min) induced a small but significant lowering of BP in lean normotensives, but failed to modify BP in obese hypertensives. L-arginine infusion (30 min, 500 mg/kg total dose) reduced BP; significantly greater reductions in systolic and diastolic BP were observed in obese hypertensives than in the control group. Both oral glucose and L-arginine induced greater increases in plasma insulin in obese hypertensives than in lean normotensives. Endothelial dysfunction which accompanies the insulin resistant state of obesity, glucose intolerance and hypertension, may account for the different BP effects induced by glucose and L-arginine in obese hypertensives and lean normotensives.

Clustering of silent cardiovascular risk factors in apparently healthy Hispanics.

Ischaemic heart disease is one of the leading causes of cardiovascular morbidity and mortality. Because most factors leading to cardiovascular disease have a silent course, early screening is needed for prevention and for halting disease progression. In our centre, a programme was implemented in apparently healthy subjects for the early diagnosis and treatment of factors known to increment the risk of developing cardiovascular and metabolic disease. We present data from the first 153 individuals evaluated. The incidence of modifiable risk factors in our healthy population was as follows: overweight 33% (BMI: 25-30 kg/m(2)), obesity 45% (BMI >30 kg/m(2)), sedentarism 84%, arterial hypertension 15% (>140/90 mm Hg), hyperinsulinaemia 50%, glucose intolerance 14% (>160 mg/dl 120 min after 75 g glucose load), type 2 diabetes mellitus 5%, hypercholesterolaemia 50%, hypertriglyceridaemia 28%, and salt sensitivity 25%. Clustering of three or more cardiovascular risk factors was observed in 59% of the apparently healthy subjects. Obesity was associated with greater clustering of risk factors. The cardiovascular dysmetabolic syndrome was present in 72% of the obese individuals. These findings revealed a very high prevalence of cardiovascular risk factors in apparently healthy Hispanics. Even though these individuals were clinically asymptomatic, they are at increased risk for developing cardiovascular disease and type 2 diabetes mellitus. Mechanisms for the early detection and correction of modifiable risk factors in the healthy population must be implemented. Only through prevention will a reduction in the incidence of cardiovascular atherosclerotic disease and of type 2 diabetes mellitus be achieved.

Urinary albumin excretion in lean, overweight and obese glucose tolerant individuals: its relationship with dyslipidaemia, hyperinsulinaemia and blood pressure.

The presence of microalbuminuria has become an important tool for therapeutic intervention. In this study we investigated whether the dysmetabolic syndrome of obesity was associated with or could occur in the absence of microalbuminuria. The study was conducted in 71 clinically healthy, glucose tolerant Hispanics (age: 43 +/- 1.4 years, body mass index (BMI): 28.7 +/- 0.6 kg/m(2), systolic blood pressure (SBP): 117 +/- 2 mm Hg, diastolic blood pressure (DBP): 77 +/- 1.3 mm Hg, urinary albumin excretion: 10.2 +/- 0.6 mg/24 h). Subjects were classified as lean (BMI <25), overweight (BMI >25 <30) and obese (BMI >30 kg/m(2)). Greater BMI was associated with higher body weight, waist-to-hip ratio (WHR), BP, fasting insulin, triglyceride, post glucose load insulin and glucose, and lower high-density lipoprotein (HDL) cholesterol levels. However, no significant differences in the urinary albumin excretion (mg/24 h) were found between lean (9.0 +/- 0.9; median: 9.1), overweight (11.3 +/- 1.2; median: 10.5) and obese (11.1 +/- 1.2; median: 9.7) subjects. In addition, microalbuminuria (urinary albumin excretion >30 mg/24 h) was not found in any of the study subjects. For all subjects combined, as well as for each of the groups separately, the urinary albumin excretion was unrelated to the BMI, WHR, body weight, triglyceride, cholesterol (total, LDL or HDL), fasting or post-load glucose and insulin plasma concentrations. Neither in females nor in males, abdominal fat accumulation was associated with an increase in the urinary albumin excretion. However, in the obese groups, urinary albumin excretion was strongly related to the level of SBP (r(2): 0.67; P < 0.0001) and DBP (r(2): 0.55; P < 0.0001). In summary, obesity, hyperinsulinaemia and dyslipidaemia per se are not determinants of increased albumin excretion. However, in the obese subjects, the BP, particularly the SBP, was a strong determinant of the level of albumin in the urine. Microalbuminuria may occur later in the course of the dysmetabolic syndrome, due to worsening of hypertension and development of hyperglycaemia.

Nitric oxide and salt sensitivity.

Studies in laboratory animals suggest that altered nitric oxide (NO) production may be associated with salt sensitivity. In this investigation we determined whether the endogenous NO production was altered in salt-sensitive human subjects when salt intake was changed. Salt sensitivity was assessed from the magnitude of the blood pressure (BP) lowering obtained when the salt intake was reduced from high to a low intake. The combined urinary excretion of nitrites and nitrates, the major metabolites of NO, was employed as an index of endogenous NO production. Salt-sensitive subjects (n = 23) were older, heavier, and had greater waist-to-hip ratios and higher baseline BP than salt-resistant individuals (n = 25). In salt-sensitive subjects, mean blood pressure (MBP) decreased 11.8+/-0.7 mm Hg, and NO metabolite excretion increased from 823+/-102 to 1530+/-148 mmol/24 h, when salt intake was reduced from 316 to 28 micromol/day. NO metabolite excretion was 45% lower during high salt (0.66+/-0.1 micromol/mg creatinine) than during low salt intake (1.12+/-0.1 micromol/mg creatinine) (P < .001). In contrast, when salt intake was reduced, salt-resistant subjects exhibited no significant mean changes in BP or NO metabolite excretion. During low salt intake, NO metabolite excretion (micromol/ day) was significantly higher in salt-sensitive individuals. The magnitude of decrease of systolic blood pressure, diastolic blood pressure, or MBP induced by reducing salt intake was not related to the increase in urinary excretion of NO metabolite levels (r2 = 0.009; P = .66). In summary, to the extent that urinary NO metabolite levels reflect the activity of the endogenous NO system, our results support the view that salt sensitivity may in part be determined by an inability to increase or to sustain NO production in response to high salt. Insufficient NO production during high salt may in turn lead to altered pressure-natriuresis relationships and to an increase in BP. The possibility that the increase in BP induced by high salt intake in salt-sensitive individuals could be the key factor in reducing NO metabolite levels can not be ruled out.

Insulin and blood pressure responses to changes in salt intake.

In this study we evaluated the role of insulin in hypertension and on salt sensitivity. The study was conducted in 47 consecutive patients attending the Center for the Detection and Treatment of Cardiovascular and Metabolic Risk factors. The relationships between fasting and post-glucose load insulin levels and the blood pressure (BP) responses to changes in salt intake, were investigated. No correlation was observed between fasting or 2-h post-load insulin levels and mean BP (MBP), systolic BP (SBP) or diastolic BP (DBP). The plasma concentrations of insulin were not significantly related to body mass index (BMI) (r2 = 0.05; P = 0.135). Neither fasting nor 2-h post-load insulin predicted the BP response to changes in salt intake. A reduction in salt intake from 316 +/- 13 to 26 PM 3 mmoles/day, produced similar BP lowering in subjects with fasting insulin >15 microU/ml and in subjects with normal fasting insulin levels (<15 microU/ml). In addition, no relationship was observed between the magnitude of the BP responses to salt and the levels of insulin, either fasting (r2 = 0.007; P = 0.86) or 2-h after a glucose load (r2 = 0.01; P = 0.213). A very strong association was found between body weight or BMI and MBP (r2 = 0.443; P< 0.0001). In conclusion, our results are against the view of a cause-effect relationship between insulin and BP levels. In addition, the insulin status of a patient does not predict (nor determines) his (her) vascular reactivity to changes in salt intake. Finally, our findings further support the existence of a strong and direct association between body weight and hypertension, and speak against a major role of insulin in the pathogenesis of hypertension associated with obesity.

Ventral and dorsal striatal cholinergic neurons have different sensitivities to kainic acid.

The present study was conducted to investigate the sensitivity of the cholinergic elements of ventral and dorsal striatal regions of the rat brain to the neurotoxin kainic acid (KA). Cholinergic activity was assessed by determining choline-acetyltransferase activity (CAT) and by measurements of acetylcholine (Ach) release from slices prelabeled with [3H]-choline. Direct stereotaxic injections of high-dose KA (4 micrograms/2 microliters) into specific brain regions, reduced CAT in caudate putamen (CP) by 91 +/- 1%, in nucleus accumbens (Nac) by 71 +/- 6%, but CAT in the olfactory tubercle (OT) was not affected by KA. The effects of KA on CP CAT were dose- and volume-dependent. In the OT, KA failed to affect CAT at low, moderate or high doses. Slices obtained from CP injected with KA (3 days prior) showed a 90% reduction in the electrically evoked release of [3H]-transmitter release; however, KA had no effect on transmitter release from OT. These results indicate that KA spares the cholinergic elements of the OT, and reveal the existence of marked differences in excitotoxic action of KA between ventral and dorsal striatal regions and among regions of the ventral striatum. Kainic acid preferentially damages neuronal cell bodies, dendrites and terminals intrinsic within the structures injected, with little or no effect on afferent axons and terminal boutons. Therefore, we propose that most of the Ach present in the OT may be within afferent axons and axon terminals. In the CP and NAc, KA lesions reflect loss of intrinsic cholinergic neurons. In addition, variable levels of excitatory inputs and of excitatory receptors, of the mechanisms available to reduce elevated intracellular calcium concentrations and of the levels of free-radical scavenging resources, also could account for the differences in KA neurotoxicity between OT and CP.

Differential effects of kainic acid on dopamine and serotonin metabolism in ventral and dorsal striatal regions.

The comparative effects of kainic acid (KA) on dopamine (DA) and serotonin (5-HT) metabolism in ventral and dorsal striatum were investigated. Local injection of KA into the caudate-putamen (CP) increased by 155% DOPAC (2,3-dihydrophenylacetic acid), by 114% HVA (homovanillic acid) and by 79% 5-HIAA (5-hydroxyindoleacetic acid) concentrations; with little or no effect on monoamine levels. The (DOPAC + HVA)/DA ratio increased from 0.33 +/- 0.2 in vehicle-treated to 0.77 +/- 0.1 in KA-treated CP. 5-HIAA/5-HT ratio increased from 2.7 +/- 0.2 to 5.9 +/- 0.1 after KA treatment. However, direct KA injections into the olfactory tubercle (OT), the most ventral part of the ventral striatum, did not alter significantly the levels of DA, 5-HT, DOPAC, HVA or 5-HIAA. Since KA is a neurotoxin which preferentially destroys perykaria and dendrites, leaving unchanged terminal boutons and axons of passage, the lack of effects on DA and 5-HT metabolism in OT suggests, that contrary to the CP, interneurons and projecting neurons in the OT play no role in inhibitory feedback mechanisms to control DA and 5-HT activities.

Comparative dopamine-acetylcholine interactions in the ventral and dorsal striatum of rabbit and rat brain.

The dopamine (DA)-acetylcholine (ACh) interactions were investigated in dorsal (nucleus caudate, NC) and ventral (olfactory tubercle, OT) striatal regions, of rats and rabbits. Both regions receive a dense dopaminergic innervation and have high ACh concentrations. Brain slices of NC and OT from both animal species were prelabeled with [3H]choline and superfused. In rat and rabbit OT and NC, higher ACh release per pulse was elicited by lower than higher stimulation frequencies; in addition, rabbit tissues released a greater fraction of tissue [3H]transmitter than rat tissues. Blockade of D2 DA-receptors with sulpiride (1 microM), did not modify ACh release in OT and NC of rats and rabbits; suggesting that the lower ACh release observed in rat tissues is not due to an inhibitory dopaminergic tone on cholinergic neurons. Apomorphine (APO), a D2 DA-receptor agonist, inhibited in a concentration-dependent manner the evoked release of ACh from rat and rabbit NC (maximal inhibition = 90%). In rabbit OT, maximal inhibition induced by APO was 49 +/- 2% and in the rat OT, it was 23 +/- 1%. Sulpiride antagonized APO-induced inhibition of ACh release from rat and rabbit NC; however, it failed to prevent APO-induced inhibition in rat OT, and in the rabbit OT reduced it from 47% to 20 +/- 5%. These results indicate differences in the wiring of DA and cholinergic neurons and terminals in dorsal and ventral striatal structures, as well as between rat and rabbit tissues. Cholinergic ventral striatal structures may not receive a direct DA input, and afferent cholinergic nerve terminals (rather than interneurons) predominate in the ventral striatum.

Differential effects of muscarinic receptor agonists and phorbol ester on muscarinic and D2-dopamine release-modulatory receptors.

The interaction between an active phorbol ester, 4-beta-phobol-12,13-dibutyrate (PDBu), and muscarinic cholinergic receptor (MAChR) agonists on the electrically evoked neurotransmitter release was studied in the striatal and prefrontal cortex (PFC) of the rabbit. MAChR agonists (carbachol and oxotremorine), physostigmine and PDBu enhanced dopamine (DA) release from striatum and prefrontal cortex. Pretreatment with PDBu antagonized the increase in DA release produced by MAChR agonists (M1 receptors). Pretreatment with MAChR agonists and physostigmine also inhibited the action of PDBu on DA release. The inhibition of ACh release from the striatum induced by MAChR agonists (M2 receptors) and by apomorphine (D2-DA receptors) was antagonized by PDBu. MAChR agonists, however, did not antagonize the effects of the D2 agonist on ACh release. In the prefrontal cortex, PDBu produced greater facilitation of DA release than in the striatum, and MAChR agonists were less effective in inhibiting the effects of PDBu on DA release. This study suggests that the facilitation of DA release induced by the MAChR agonists and that induced by PDBu occur via a similar mechanism: stimulation of protein kinase C. PDBu induces a broad-spectrum loss of responsiveness to M1-MAChR and M2-MAChR and to D2-DA release-modulatory receptors, which is probably due to massive protein kinase C stimulation, signaling cell overstimulation. MAChR agonists, on the other hand, would stimulate the protein kinase C in close proximity to the M1 ACh receptor, facilitating DA release but failing to induce broad-spectrum desensitization.

Behavior of mesocortical dopamine terminals during single and repetitive stimulation: comparison with nigrostriatal neurons.

The present study reinvestigates the role of autoinhibition in dopamine (DA) release from mesoprefrontal and nigrostriatal DA neurons using improved methodology. Slices of rabbit prefrontal cortex (PFC) and striatum (STR) were labeled with [3H]DA and superfused in the presence of nomifensine (3 microM). Overflow was elicited by field stimulation with a single pulse (autoinhibition-free condition) or trains of pulses (4, 16 and 64) delivered at 0.05 to 30 Hz. One-pulse stimulation caused a measurable overflow of tritium in the PFC and STR (0.12% vs. 0.21% of tissue tritium, respectively). At increasing numbers of pulses, per-pulse over-flow decreased at all frequencies, but it was consistently more pronounced in the STR than in the PFC (e.g., 64 pulses/3 Hz: -30% PFC, -70% STR). The frequency dependence of DA release was biphasic at all numbers of pulses with overflow largest at 0.05 Hz and smallest at 3 Hz. In the PFC, however, the magnitude of the changes was considerably smaller, and the per-pulse release at higher frequencies was much larger than in the STR. The DA D2-receptor antagonist sulpiride (3 microM) enhanced pulse-train-evoked overflow from the STR at all frequencies between 0.3 and 10 Hz, whereas facilitation in the PFC was achieved at 10 Hz only. One-pulse-evoked overflow was not facilitated by sulpiride in either region. In conclusion, DA overflow from PFC terminals is not generally higher than overflow from STR terminals, as suggested in earlier studies. Larger per-pulse overflow from mesoprefrontal DA neurons occurs only under intense stimulation and is only in part a consequence of weak autoinhibition in this region.

Participation of serotonin on early and delayed emesis induced by initial and subsequent cycles of cisplatinum-based chemotherapy: effects of antiemetics.

The role of serotonin as the possible trigger mechanism of vomiting associated with chemotherapeutic drugs was further investigated in cancer patients (n = 86). Increases in 5-hydroxyindoleacetic acid (5-HIAA) excretion rates (2.5-2.9 times baseline values) were observed 4 to 8 hours after high-dose cisplatinum (> or = 50 mg/m2). The daily excretion of 5-HIAA from 24-48, 48-72, and 72-96 hours after cisplatinum was not different from pre-cisplatinum levels. These results, together with the efficacy data for 5-HT3 antagonists, suggests that serotonin may trigger the early, intense period of emesis, but not the period of delayed emesis, following high-dose cisplatinum. Compared with the first cycle of chemotherapy, higher peak levels and more sustained elevations of 5-HIAA excretion were found after subsequent cycles, with high-dose cisplatinum. Further, no evidence of serotonin depletion was found after a single or after repeated cycles of treatment with high-dose cisplatinum. These data suggest that the more intense emetic response associated to repeated cycles of treatment may be triggered by greater changes in serotonin release. No significant differences in the rate and amount of 5-HIAA excreted induced by low-dose (30 +/- 2 mg/m2) and high-dose (84 +/- 3 mg/m2) cisplatinum were found between those patients who received dexamethasone (D) (20 mg i.v.) and those who received metoclopramide (M) (2 mg/kg, i.v.), irrespectively of the cycle of treatment. Interestingly, for M but not for D, best antiemetic protection was observed when lower amounts of serotonin were released (i.e., low-dose cisplatinum and initial cycles of treatment).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in serotonin metabolism in cancer patients: its relationship to nausea and vomiting induced by chemotherapeutic drugs.

The metabolism of serotonin was studied in cancer patients of their first day of their first course of chemotherapeutic drugs either with strongly or moderately emetogenic regimens. It was observed that strongly emetogenic treatments induce greater increases in serotonin release than moderately emetogenic regimens. High-dose cisplatinum (75 +/- 5 or 83.8 +/- 5 mg m-2) produced a marked increase in the plasma levels and in the urinary excretion of 5-hydroxyindole acetic acid (5-HIAA). Neither platelet nor plasma (platelet-free plasma) serotonin were significantly modified by high-dose cisplatinum. Dacarbazine (283 +/- 22 mg m-2), another strongly emetogenic agent, induced acute nausea and emesis paralleled by marked increases in the urinary excretion of 5-HIAA. Both for high-dose cisplatinum and dacarbazine, the increases in serotonin metabolism occurred with a similar time-course than those of vomiting, and lasted for a period of 4 to 8 h. Low-dose cisplatinum (30.8 +/- 3 mg m-2) as well as cyclophosphamide-based chemotherapies (520 +/- 30 mg m-2) produced very small increases in the urinary excretion of 5-HIAA. Platelet and plasma serotonin levels failed to increase in cyclophosphamide-treated patients. Octreotide, a long-acting somatostatin analog, did not inhibit the increase in urinary 5-HIAA and the nausea and vomiting produced by high-dose cisplatinum. These results suggest that for treatments that induce marked increases in serotonin release such as high-dose cisplatinum or dacarbazine: (a) the amount and time course of serotonin release induced by chemotherapeutic drugs determines the severity, time of onset and pattern of emesis observed; (b) platelet serotonin play no role in chemotherapy-induced emesis; (c) strongly emetogenic regimens release serotonin from enterochromaffin cells; and (d) intestinal release of serotonin is the consequence of the damage induced by the chemotherapeutic drugs on the gut mucosa.

Carbachol-phorbol ester interactions at muscarinic receptors modulating dopamine release from rabbit striatal slices.

Both 4-beta-12,13-dibutyrate phorbol-ester (PDBu) (EC50% = 82 +/- 12 nM) and carbachol (EC50% = 2.3 +/- 0.3.5 microM) enhanced dopamine (DA) release from rabbit striatal slices. No additivity was observed when slices were treated simultaneously with 0.1 microM PDBu and 10 microM carbachol. Pretreatment with PDBu (0.01-0.1 microM) abolished carbachol-induced facilitation of DA release. Pretreatment with carbachol (3-100 microM) antagonized the enhancement in DA release produced by PDBu. The effect of carbachol was blocked by atropine (0.1 microM) and not by hexamethonium (10 microM). The effect of PDBu was not modified by the acetylcholine receptor (AChR) antagonists. If muscarinic (MAChR) MAChR were blocked by atropine (0.1 microM), pretreatment with carbachol failed to antagonize PDBu-induced facilitation of DA release. This is the first report to indicate that activation of M1-MAChR by an agonist prevents the effects of an active phorbol-ester. We suggest that activation of M1-MAChR enhances DA release possibly through activation of PKC.

Efficacy of ondansetron (GR 38032F) and the role of serotonin in cisplatin-induced nausea and vomiting.

We compared the efficacy and safety of ondansetron (GR 38032F), a selective antagonist of serotonin S3 receptors, with that of placebo in controlling the nausea and vomiting induced by cisplatin treatment in 28 patients with cancer. The patients received either three intravenous doses of ondansetron (0.15 mg per kilogram of body weight) or normal saline (placebo) at four-hour intervals, beginning 30 minutes before the administration of cisplatin. Nausea and vomiting were markedly diminished in the group given ondansetron. The median time to the first episode of emesis was 2.8 hours in the placebo group and 11.6 hours in the ondansetron group (P less than 0.001); the median number of episodes in 24 hours was 5.5 in the placebo group and 1.5 in the ondansetron group (P less than 0.001); the mean (+/- SEM) number of regurgitations or dry heaves per episode was 3.2 +/- 0.5 in the placebo group and 1.17 +/- 0.1 in the ondansetron group (P less than 0.001). None of the 14 patients given ondansetron, but 12 of 14 given placebo, required treatment with antiemetic-rescue agents for the control of nausea and vomiting. There were no adverse effects attributable to ondansetron. The urinary excretion of 5-hydroxyindoleacetic acid, the main metabolite of serotonin, was increased in all patients two to six hours after they received cisplatin chemotherapy, and the increases paralleled the episodes of emesis. We conclude that ondansetron is an effective and safe agent for controlling the nausea and vomiting induced by cisplatin treatment. We suggest that cisplatin treatment increases the release of serotonin from enterochromaffin cells, and that ondansetron acts by blocking S3 receptors for serotonin.

Is the release of dopamine from medial prefrontal cortex modulated by presynaptic receptors? Comparison with nigrostriatal and mesolimbic terminals.

Results obtained from our in vitro studies employing superfused slices obtained from three functionally different brain regions rich in DA axon terminals were discussed. Striking qualitative and quantitative similarities were found for the modulation of DA release from the nucleus caudate and the OT of the rabbit. However, the PFC DA terminals showed important differences from the nigrostriatal and mesolimbic DA terminals. Although release modulatory D2 DA autoreceptors could also be demonstrated in superfused slices of the PFC, our results suggest that the cortical nerve terminals may have a lower number of functional autoreceptors or a reduced efficiency of coupling between receptors and inhibition of release. Either possibility could explain (a) the poor inhibitory efficacy of the agonists, (b) the small facilitatory effect of the antagonists, (c) the disproportionate increase in transmitter overflow produced by neuronal uptake inhibitors, and (d) the lack of synergism between uptake inhibitors and DA antagonists. When the efficacy of the autoreceptor mechanisms was evaluated at stimulation frequencies comparable to the in vivo firing rates reported for each of the three neuronal groups, it was found that DA release from the striatum and the OT was tightly modulated by presynaptic D2 DA receptors; whereas release from PFC was not. We propose that the autoreceptor-mediated control of DA release from PFC may not function in vivo, even though modulation of release by presynaptic D2 DA receptors from PFC terminals could be demonstrated under specific experimental conditions in vitro. However, it is envisaged that if in vivo firing rate of the PFC DA neurons is reduced, the inhibitory actions of DA agonists on DA release may be regained. From these and other studies it is apparent that drug effects on autoreceptors are highly dependent on the rate and duration of stimulation applied to a specific neuronal group. We propose that the basal status of activity of a specific neuronal target could determine the type and magnitude of the effect produced by a therapeutic agent acting at release modulatory receptors. The neuronal activity (firing rate and pattern) may be affected by physiological status, disease, and by current or previous drug treatments. The mechanisms by which PFC DA terminals release a larger proportion of their storage pool compared to other mesotelencephalic DA terminals is unknown and may represent a compensatory mechanism to the continuous rapid firing rates at which these neurons are exposed in vivo.(ABSTRACT TRUNCATED AT 400 WORDS)