Circadian timing and alignment in healthy adults: associations with BMI, body fat, caloric intake and physical activity.

INTRODUCTION: Disruption of circadian rhythms is one of the proposed mechanisms linking late sleep timing to obesity risk but few studies have evaluated biological markers outside of the laboratory. The goal of this study was to determine the relationship between the timing and alignment of melatonin and sleep onset (phase angle) with body mass index (BMI), body fat and obesity-related behaviors. We hypothesized that circadian alignment (relationship of melatonin to sleep timing) rather than circadian (melatonin) timing would be associated with higher BMI, body fat, dietary intake and lower physical activity. SUBJECTS/METHODS: Adults with sleep duration ⩾6.5 h completed 7 days of wrist actigraphy, food diaries and SenseWear arm band monitoring. Circadian timing, measured by dim light melatonin onset was measured in the clinical research unit. Circadian alignment was calculated as the duration between dim light melatonin onset and average sleep onset time in the prior week (phase angle). Body fat was evaluated using dual-energy X-ray absorptiometry. Data were analyzed using bivariate correlations and multivariable regression analyses controlling for age, sex, sleep duration and evening light exposure. RESULTS: Participants included 97 adults (61 F, age 26.8±7.3 years) with average sleep duration 443.7 (s.d.=50.4) minutes. Average phase angle was 2.2 h (s.d.=1.5). Circadian alignment was associated with circadian timing (P<0.001) and sleep duration (P=0.005). In multivariable analyses, later circadian timing was associated with lower BMI (P=0.04). Among males only, circadian alignment was associated with percent body fat (P=0.02) and higher android/gynoid fat ratio (P=0.04). Circadian alignment was associated with caloric intake (P=0.049) carbohydrate intake (P=0.04) and meal frequency (P=0.03) among both males and females. CONCLUSION: Circadian timing and alignment were not associated with increased BMI or body fat, among healthy adults with ⩾6.5 h of sleep, but circadian alignment was associated with dietary intake. There may be sex differences in the relationship between circadian alignment and body fat.

Pharmacological characterization of a new Ca(2+) sensitizer.

The benzimidazole molecule was modified to synthesize a Ca(2+) sensitizer devoid of additional effects associated with Ca(2+) overload. Newly synthesized compounds, termed 1, 2, 3, 4, and 5, were evaluated in spontaneously beating and electrically driven atria from reserpine-treated guinea pigs. Compound 3 resulted as the most effective positive inotropic agent, and experiments were performed to study its mechanism of action. In spontaneously beating atria, the inotropic effect of 3 was concentration-dependent (3.0 microM-0.3 mM). Compound 3 was more potent and more active than the structurally related Ca(2+) sensitizers sulmazole and caffeine, but unlike them it did not increase the heart rate. In electrically driven atria, the inotropic activity of 3 was well preserved and it was not inhibited by propranolol, prazosin, ranitidine, pyrilamine, carbachol, adenosine deaminase, or ruthenium red. At high concentrations (0.1-1.0 mM) 3 inhibited phosphodiesterase-III, whereas it did not affect Na(+)/K(+)-ATPase, sarcolemmal Ca(2+)-ATPase, Na(+)/Ca(2+) exchange carrier, or sarcoplasmic reticulum Ca(2+) pump activities of guinea pig heart. In skinned fibers obtained from guinea pig papillary muscle and skeletal soleus muscle, compound 3 (0.1 mM, 1 mM) shifted the pCa/tension relation curve to the left, with no effect on maximal tension and no signs of toxicity. Compound 3 did not influence the basal or raised tone of guinea pig isolated aorta rings, whose cells do not contain the contractile protein troponin. The present results indicate that the inotropic effect of compound 3 seems to be primarily sustained by sensitization of the contractile proteins to Ca(2+).

Endothelium is required in the vascular spasm induced by tetraethylammonium and endothelin-1 in guinea-pig aorta.

1. To investigate the role of endothelium in vascular spasm, we studied the influence of endothelin-1 (ET-1) on the contracting and spasmogenic effect of the K+-channel blocker, tetraethylammonium (TEA), in aorta rings of reserpine-treated guinea-pigs, perfused with either control (5.5 mM) or elevated (50 mM) glucose concentration. 2. Endothelium-dependent relaxation induced by acetylcholine was lost in rings contracted by noradrenaline in the presence of elevated glucose. In control medium, TEA (1-20 mM) induced a sustained tonic contraction, followed by a phasic spasm, characterized by rhythmic contractions. Elevated glucose, ET-1 (3 nM), or both, reduced the EC50 of TEA-induced tonic contraction, without modifying the maximum contractile effect. 3. In control medium, ET-1 reduced the time before TEA-induced spasm and increased the rate of rhythmic contractions. TEA-induced spasm was abolished by elevated glucose, and restored by ET-1. The spasm induced by TEA and ET-1 was amplified by the ETA antagonist, EMD94246, and suppressed by the ET(A)-ET(B) antagonist, bosentan. In endothelium-denuded vessels incubated with high glucose and ET-1, TEA evoked only a tonic contraction. 4. In control medium, L-NAME (N(G)-nitro-L-arginine methyl ester) abolished TEA-induced rhythmic contractions. L-arginine, but not D-arginine, prevented the effect of L-NAME. In the presence of elevated glucose and ET-1, TEA-induced spasm was not affected by L-NAME, whereas verapamil, indomethacin, metyrapone, glybenclamide or apamin abolished the phasic spasm, unmasking the tonic contracture. 5. In conclusion, endothelium plays a regulatory role in the genesis and maintenance of TEA-induced rhythmic contractions, through the release endothelium derived relaxing factor and vasodilating eicosanoids.

Early reduction in plasma norepinephrine during beta-blocking therapy with metoprolol in chronic heart failure.

BACKGROUND: The possible role exerted by modulation of sympathetic outflow in the clinical effects of beta-blockade in chronic heart failure was tested during short- and long-term treatment. METHODS AND RESULTS: Oral metoprolol (30-150 mg/day) was added to conventional therapy in 14 patients with idiopathic dilated cardiomyopathy, left ventricular ejection fraction (LVEF) of <0.45, and New York Heart Association class II or III. Norepinephrine plasma levels, which are an index of sympathetic activation, decreased by 27.57 +/- 18.03% after 1 month (P < .005), but returned to pretreatment levels after 6 months. LVEF increased by 7.7 +/- 6.0 ejection fraction units after 6 months (P < .005 vs baseline and P < .05 vs 1 month). Long-term beta-blockade resulted in nonsignificant improvements in functional class, symptom score, and oxygen consumption at peak exercise. After 1 month, the reduction in plasma norepinephrine levels and the changes in LVEF were inversely correlated (P < .01). No other correlation emerged during short- or long-term treatment. CONCLUSION: In conclusion, the reduction in plasma norepinephrine levels during short-term beta-blockade was not proportional to the clinical benefits and may have been attributed to the direct inhibition of sympathetic outflow. The early reduction in circulating norepinephrine levels may decrease cardiac performance through withdrawal of sympathetic support when the favorable effects of beta-blockade have not had time to occur. The role that sympathetic modulation may exert in the long-term clinical benefits of metoprolol deserves further investigation.

Impairment of endothelium-dependent but not of endothelium-independent dilatation in guinea-pig aorta rings incubated in the presence of elevated glucose.

1. Purine compounds such as ATP and adenosine, respectively endothelium-dependent and- independent vasodilators, are largely involved in the control of vascular tone and vascular reactivity to contracting stimuli. We investigated the relaxing activity of ATP and adenosine in guinea-pig aorta rings exposed for 6 h to elevated glucose concentration (50 mM), in order to mimic hyperglycaemic conditions. Guinea-pigs were reserpine-treated (2 mg kg-1, i.p., 48 and 24 h before death). 2. Rings of aortae incubated in 50 mM glucose, contracted submaximally by 1 microM noradrenaline, lost endothelium-dependent relaxation in response to acetylcholine (10 nM to 10 microM). Aortae incubated with 50 mM mannose, as a hyperosmotic control, relaxed to acetylcholine normally. Rings of aortae incubated in 50 mM glucose, contracted submaximally by 3 mM 4-aminopyridine, lost endothelium-dependent relaxation in response to ATP (30 microM) whereas endothelium-independent relaxation in response to adenosine (0.3 mM) was well preserved. 4. The relaxation induced by A23187 or sodium nitroprusside (10 nM to 0.1 microM) did not differ between rings exposed to control (5.5 mM) or elevated glucose (50 mM) and contracted submaximally by 3 mM 4-aminopyridine. 5. When incubated with aortic tissue in the presence of elevated glucose, the cyclo-oxygenase inhibitors, indomethacin (10 microM) and mefenamic acid (30 microM), or the scavenger of superoxide anions, superoxide dismutase (150 u ml-1), prevented the impairment of ATP-mediated relaxation. 6. The present results indicate that endothelium-dependent, receptor-induced relaxation in response to acetylcholine and ATP is impaired in guinea-pig aorta rings exposed to elevated glucose. The endothelial dysfunction caused by glucose might be located at a step between receptor activation and intracellular calcium increase, and might be related to an increased metabolism of arachidonic acid coupled to an increased production, or to a reduced inactivation of superoxide anions.

New inotropic agents: milrinone analogs.

1. Two new milrinone analogs, 3-acetyl-6-phenyl-2(1H)-pyridone (SF 348) and 3-acetyl-7-methyl-7,8-dihydro-2,5(1H, 6H) quinolinone (SF 349), increase the contractile activity of spontaneously beating and electrically driven atria isolated from reserpine-treated guinea-pigs. 2. Propranolol 0.1 microM drastically inhibits the contractile effect of SF 348, whereas that of SF 349 is unaffected. Preincubation of the atria with adenosine-deaminase suppresses the cardiac activity of SF 349, but does not affect that of SF 348. 3. SF 349 competitively antagonizes the negative inotropic effect induced by N6-(R-phenylisopropyl)-adenosine (R-PIA) and displaces N6-cyclohexyl[3H]-adenosine (3H-CHA) from its binding sites to A1 receptors in the guinea-pig heart. 4. The positive inotropic effect of SF 348 is largely sustained by activation of beta-adrenoceptors, whereas SF 349 acts by displacing endogenous adenosine from its inhibitory (A1) receptors in the atria.

Synthesis and cardiotonic activity of novel pyrimidine derivatives: crystallographic and quantum chemical studies.

The synthesis of ethyl or methyl 4-substituted or unsubstituted 2-(dimethylamino)-5-pyrimidinecarboxylates 10-20, which is mainly carried out by reaction of ethyl or methyl 2-[(dimethylamino)methylene]-3-oxoalkanoates with 1,1-dimethylguanidine, is described. The above esters were hydrolyzed to the relative carboxylic acids 21-30, which were decarboxylated to the corresponding 2,4-disubstituted pyrimidines 31-40. All the new synthesized pyrimidines were evaluated in spontaneously beating and electrically driven atria from reserpine-treated guinea pigs. Their effects were compared to those induced by milrinone in both atria preparations. Compound 28 (4-benzyl-2-(dimethylamino)-5-pyrimidinecarboxylic acid) was the most effective positive inotropic agent, while the corresponding methyl ester 17 reduced both the contractile force and the frequency of guinea pig atria. An antagonism toward the negative influence exerted by endogenous adenosine on the heart seems to be involved in the contractile activity of compound 28. By contrast, compound 17 might be partial agonist at the purinergic inhibitory (A1) receptor. X-ray analysis carried out on 17 and 28 and molecular modeling investigations extended also to related derivatives allowed a possible rationalization between structure and inotropic activity for this series of compounds.

[Hemodynamics and clinical data in chronic coronary disease with severe left ventricular systolic dysfunction]. / Emodinamica centrale e dati clinici nella coronaropatia cronica con grave disfunzione sistolica ventricolare sinistra.

To elucidate how symptoms and signs of chronic heart failure are related to the filling pressure and cardiac output at rest, 58 patients (55 males, 3 females, mean age 57 +/- 9 years, range 30-75) with left ventricular ejection fraction (LVEF) < or = 30% and a lesion > or = 50% on a major coronary branch have been selected from patients submitted in 1985-1993 to a complete right and left cardiac catheterization including ventriculography and coronary angiography. Patients with recent myocardial infarction (MI), unstable angina, associated heart diseases or recent changes in body weight and in diuretic therapy were excluded. Clinical data were obtained at cardiac catheterization time from history, physical examination, chest X-ray and ECG. Patients with angina as limiting symptom were excluded from NYHA functional classification. Pulmonary venous congestion (PVC) was defined on X-ray as: absent, venous redistribution, interstitial pulmonary edema (IPE). Mean pulmonary capillary wedge pressure (PCWP) was recorded under fluoroscopy and cardiac index was measured by the Fick method. On the whole group, 96% of patients had had one or more MI (on ECG necrosis was anterior in 58%, inferior in 9%, anterior and inferior in 26%), 69% were in NYHA functional class III or IV, 54% had IPE and 45% had mitral regurgitation. 71% were under treatment with digitalis, 74% with diuretics and 39% with ACE-inhibitors. PCWP was correlated with LVEDV (r = 0.34; p < 0.001) but neither with LV mass nor with LV mass/volume ratio. It was significantly higher (p < 0.01) in patients with mild-moderate mitral regurgitation, in patients with necrosis involving both anterior and inferior walls (26 +/- 6 vs 21 +/- 8 mmHg in patients with single wall necrosis, p < 0.05) and in patients with multiple MI (26 +/- 7 vs 20 +/- 8 mmHg in patients with no or single MI, p < 0.02). Moreover, it was neither correlated with functional classification nor with PVC: of patients with PCWP > 24 mmHg, 14% were in II NYHA functional class and 21% had no PVC while of patients with PCWP < 15 mmHg, 36% were in NYHA functional class IV and 7% had IPE. Cardiac index was reduced below 2.3 l/min/m2 in 21% of patients: these patients had increased pulmonary (p < 0.0002) and systemic (p < 0.0001) vascular resistance, increased systolic (p < 0.001) and diastolic (p < 0.01) pulmonary artery pressure and reduced LVEF (p < 0.01) and right ventricular ejection fraction (p < 0.03). Furthermore, on the whole patients an inverse correlation was found between cardiac index and functional classification (r = -0.42; p < 0.01). The reliability of NYHA functional class IV, physical signs of heart failure and IPE for estimating PCWP > 24 mmHg and cardiac index < 2.3 l/min/m2 was rather limited although high specificity was shown for gallop sounds (92 and 97%) and jugular vein distension (88 and 97%). In conclusion, in coronary patients with chronic severe LV systolic dysfunction a mismatch between clinical data and central hemodynamics is not rare. The reliability of functional class, X-ray PVC and physical signs to predict central hemodynamics in fairly limited.

Chemical and pharmacological characterization of Erythrophleum lasianthum alkaloids.

Two alkaloids 1 and 2 were isolated from the seeds of Erythrophleum lasianthum. Their structures were assigned by spectroscopic and chemical means as 3 beta-hydroxynorerythrosuamine (1) and its 3-O-beta-D-glucopyranoside (2). In spontaneously beating atria, both compounds 1 and 2 showed a marked and concentration-dependent positive inotropic activity and a weak negative chronotropic activity. The positive inotropic effect induced by 1 and 2 was not modified by propranolol, prazosin, carbachol, and ranitidine plus pyrilamine. Both 1 and 2 were very active in inhibiting the Na+/K(+)-ATPase isolated from bovine cardiac sarcolemmal vesicles.

Influence of beta-blockade with metoprolol on symptoms and functional capacity of patients with idiopathic dilated cardiomyopathy.

Long-term treatment with beta-adrenergic blocking drugs has been shown to induce clinical amelioration in patients with chronic heart failure. However, the efficacy of these agents has not been consistent, and the mechanisms of their beneficial effects remain to be established. The present study evaluated the influence of oral metoprolol on symptoms and exercise tolerance of patients with idiopathic dilated cardiomyopathy (3 women and 9 men, left ventricular ejection fraction < 0.45, NYHA functional class II or III). One patient did not tolerate metoprolol, whereas 11 patients terminated the study. After 6 months of beta-blocking therapy, detectable improvements of symptoms (NYHA class and questionnaire-derived symptom score) were observed in 6 patients. Six patients reported an increase in functional capacity [oxygen consumption at peak exercise (VO2p) during cardiopulmonary exercise test]. For the whole group, no significant changes in symptoms and exercise tolerance were detected. During exercise, oxygen pulse (VO2/heart rate) and VO2/RPP (VO2/heart rate/systolic pressure) were significantly increased after 6 months on metoprolol (+35, 9% and +27.1%, respectively; both p < 0.01 vs baseline). In conclusion, beta-blocking therapy was well tolerated by the majority of patients, some of which reported improvement of symptoms and functional capacity. The observed increase on oxygen pulse and Vo2/RPP suggests that beta-blockade may reduce myocardial oxygen requirements in proportion to cardiac work. An increase in the energy available to myocardial cells for synthetic and reparative processes may thus account, at least in part, for the beneficial influence of long-term beta-blockade in heart failure patients.

Synthesis and pharmacological activities of ethyl 5-cyano-1,6-dihydro-6-oxo-2-(2,3,4-pyridyl)-3-pyridinecarboxylates and derivatives.

The synthesis of ethyl esters of 5-cyano-1,6-dihydro-6-oxo-3-pyridinecarboxylic acids carrying as 2-substituent the 2-,3- or 4-pyridyl group is described. By alkaline hydrolysis followed by acidification, these esters gave the corresponding carboxylic acids, which were decarboxylated to 1,2-dihydro-2-oxo-6-(2,3,4-pyridyl)-3-pyridinecarbonitriles. As milrinone analogues, the above compounds were tested on contractile activity and frequency rate of spontaneously beating atria from reserpine-treated guinea-pigs. Ethyl 5-cyano-1,6-dihydro-6-oxo-2-(2-pyridyl)-3-pyridinecarboxylate showed an appreciable positive inotropic activity, although inferior to that of milrinone; moreover, some other compounds bearing the above 2-substitution pattern showed interesting antiinflammatory, analgesic and hypotensive activity.

Pharmacological characterization of a new milrinone analogue.

In a new series of milrinone analogues (esters of 2-substituted 5-acetyl-1,6-dihydro-6-oxo-3-pyridinecarboxylic acids), ethyl 5-acetyl-1,6-dihydro-6-oxo-2-phenyl-3-pyridinecarboxylate (compound 2f) has been found to be more potent and more effective than milrinone as a positive inotropic agent while affecting only marginally the frequency rate of guinea-pig isolated atria. This finding prompted us to study the mechanism of cardiac action of compound 2f in electrically driven left atrium from reserpine-treated guinea pigs. Compound 2f induced a statistically significant increase in the contractile force at a concentration as low as 1 microM, while the minimum effective concentration of milrinone was 10 microM. The beta-blocker propranolol (0.1 microM) caused a marked inhibition of the inotropic effect of compound 2f. Adenosine deaminase (1 and 2 U/ml) inhibited significantly and in a concentration-dependent manner the increase in inotropism induced by compound 2f and the adenosine deaminase-resistant response was abolished by 0.1 microM propranolol. In the presence of 0.1 microM propranolol, compound 2f (5 to 30 microM) antagonised in competitive manner the negative inotropic effect induced by N6-(R-phenylisopropyl) adenosine (R-PIA) (0.01-1.0 microM), a stable adenosine receptor agonist. Schild regression analysis gave in fact a slope of 1.02 +/- 0.06 and the pA2 value for compound 2f was 5.41 +/- 0.28. Compound 2f also inhibited phosphodiesterase (PDE) III isolated from calf heart, this inhibition being quantitatively significant only at the highest concentrations tested (0.5 M to 1 mM).(ABSTRACT TRUNCATED AT 250 WORDS)

Increased toxicity of anthracycline antibiotics induced by calcium entry blockers in cultured cardiomyocytes.

Calcium channel blocking drugs have been reported to reduce survival rate of laboratory animals treated with cardiotoxic antitumor anthracyclines. In order to elucidate the mechanisms of this drug interaction, cell toxicity of the anthracyclines, doxorubicin and daunorubicin, was evaluated in primary cultures of cardiac myocytes isolated from neonatal rats. Low concentrations of extracellular calcium ([Ca2+]0) and addition of calcium entry blockers (nifedipine or flunarizine) potentiated myocardial toxicity of anthracyclines as assessed by the release of lactate dehydrogenase from the cells. Accumulation of anthracyclines in the cardiomyocytes was increased by calcium entry blockers (nifedipine, flunarizine, and verapamil) and by low [Ca2+]0; efflux of [3H]daunorubicin from myocardial cells was inhibited by nifedipine. At a dose that exerts only modest calcium channel activity, R-verapamil failed to affect doxorubicin accumulation in cardiomyocytes, whereas the calcium channel activator, (+/-)-Bay K-8644, reduced the retention of anthracyclines; the calcium channel activity is thus required in order to increase the accumulation of anthracyclines in myocardial cells. Calcium channel blockers are also known to increase intracellular retention and toxicity of chemotherapeutic drugs in multidrug resistant tumor cells by inhibiting the efflux of cytotoxic agents from cells; however, the ability of the interacting drugs to inhibit the efflux of chemotherapeutic agents from tumor cells is not dependent on the calcium channel blocking activity. Therefore, the mechanism(s) by which calcium channel blocking drugs increase the accumulation of anthracyclines in resistant tumor cells and myocardial cells may be different. In accordance with previous investigations, the present in vitro study confirmed that anthracycline-induced cardiotoxicity may be potentiated by calcium channel blocking drugs. This indicates that, in the association of antineoplastic drugs with agents that reverse multidrug resistance, the potential exists for enhanced damage of normal cells and tissues; further studies are needed to evaluate the relevance of this adverse interaction.

MPTP-induced ATP depletion and cell death in neuroblastoma X glioma hybrid NG 108-15 cells: protection by glucose and sensitization by tetraphenylborate.

The toxic effect of the Parkinsonism-producing neurotoxin MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) was investigated using a neuronal cell culture system, namely, neuroblastoma X glioma hybrid NG 108-15. The cells were able to metabolize MPTP into its active metabolite MPP+ (1-methyl-4-phenylpyridinium ion) and to convert its derivative, 2'-methyl MPTP, to the corresponding pyridinium ion. Degenerative changes were observed in NG 108-15 cells when they were examined with a phase-contrast microscope following exposure to MPTP, MPP+, or 2'-methyl MPTP. These compounds also caused an increased leakage of LDH from the treated cells. An enhanced release of [14C]adenine nucleotides was observed from treated cells which were prelabeled with [14C]adenine. The cell death as indicated by the leakage of LDH and the release of adenine nucleotides was markedly reduced in the presence of a high concentration (25 mM) of glucose in the medium. MPTP and MPP+ induced a drastic depletion in cell ATP content prior to cell death. The ATP depletion was also reduced by the presence of a high concentration of glucose. In contrast, tetraphenylborate, a lipophilic anion, highly potentiated the ATP depletion and the subsequent cell death induced by MPTP. Thus, ATP depletion could be a major factor in MPTP-induced neuronal cell death.

Maitotoxin-induced myocardial cell injury: calcium accumulation followed by ATP depletion precedes cell death.

Maitotoxin, the most potent marine toxin, is known to increase the uptake and the accumulation of Ca2+ into cells, and was used in the present study to investigate the mechanisms of myocardial cell damage induced by Ca2+ overload. In cultured cardiomyocytes, isolated from 2-day-old rats, maitotoxin affected cell viability, as indicated by the leakage of the cytosolic enzyme lactate dehydrogenase (LDH) and of radiolabeled adenine nucleotides into the extracellular medium. Maitotoxin-induced leakage of LDH steadily increased between 30 min and 24 hr, and was preceded by a marked depletion of intracellular ATP. Addition of maitotoxin resulted in a rapid influx of extracellular Ca2+, as detected by preincubating the cells in the presence of 45Ca; this effect evolved in a few minutes, thus preceding the signs of cell death. Cytosolic levels of free Ca2+ ([Ca2+]i) were monitored by loading freshly isolated, suspended cardiomyocytes with the intracellular fluorescent probe fura-2; in these cells, maitotoxin induced a dose-dependent increase in [Ca2+]i, with a lag phase of less than a minute. All these effects of maitotoxin were inhibited by reducing Ca2+ concentration in the culture medium or by incubating the cells with the calcium-channel blocking drug verapamil. It is thus demonstrated that maitotoxin-induced cardiotoxicity is secondary to an inordinate influx of Ca2+ into the cells. It is also suggested that, in those conditions that lead to an inordinate accumulation of Ca2+ into myocardial cells, the unmatched demands of energy and the depletion of ATP play a primary role in the irreversible stage of cell damage.

Maitotoxin-induced liver cell death involving loss of cell ATP following influx of calcium.

Maitotoxin, one of the most potent marine toxins known, produced cell death in cultures of rat hepatocytes with a TD50 of 80 pM at 24 hr. The cell death, as indicated by a dose- and time-dependent leakage of lactate dehydrogenase (LDH), was also associated with the leakage of [14C]adenine nucleotides from hepatocytes prelabeled with [14C]-adenine. The toxic effect of maitotoxin was completely abolished by the omission of calcium from the culture medium. The cell death induced by maitotoxin increased with increasing concentrations of calcium in the medium. Treatment of hepatocytes with low concentrations of the toxin (less than 0.5 ng/ml) resulted in increases in 45Ca influx into the cells. At higher concentrations of maitotoxin (greater than 1ng/ml), the initial increase in 45Ca influx was followed by the release of the 45Ca from the cells into the medium. Since the 45Ca release paralleled the LDH leakage, the release of calcium was due to cell death. The 45Ca influx, [14C]adenine nucleotide leakage, and LDH leakage were effectively inhibited by verapamil, a calcium channel blocker. Maitotoxin also induced a time- and dose-dependent loss of ATP from hepatocytes, which preceded the [14C]adenine nucleotide and LDH leakage. Thus, it appears that the cell death resulting from maitotoxin treatment is caused by the elevated intracellular calcium, which in turn inhibits mitochondrial oxidative phosphorylation causing depletion of cell ATP. Loss of cell ATP may be the causative event in the maitotoxin-induced cell death.

[Efficacy of diltiazem in blood pressure increase caused by exertion]. / Efficacia del diltiazem sull'incremento pressorio da sforzo.

After examining the properties of the 3 most widely used calcium antagonists, the paper assesses the efficacy of Diltiazem in reducing blood pressure rises after exercise in a group of 7 patients with chronic atrial fibrillation. The blood pressure response to a standard load (50 W x 3 m2) on the exercise cycle was monitored in a group of patients under chronic digitalis treatment (phase I) after which the same patients' response to varying doses of Diltiazem (180-240 mg/day) was assessed (phase II) and finally (phase III) their response to treatment with Diltiazem alone but no digitalis. A significantly greater reduction in the systolic pressure and heart rate after exercise was noted in patients given Diltiazem with or without Digoxin than in those given digitalis alone. It is therefore concluded that Diltiazem may be useful in controlled blood pressure and heart rate increases after exercise, especially in patients with ischaemic heart disease.

Low- and medium-dose diltiazem in chronic atrial fibrillation: comparison with digoxin and correlation with drug plasma levels.

The safety and efficacy of diltiazem were compared with digoxin maintenance therapy for control of ventricular response in 19 patients with chronic atrial fibrillation. The relationship between drug plasma levels and cardiovascular effects was also investigated. After 7 days of combined therapy with diltiazem (60 mg three times a day in 10 patients and four times a day in nine patients) and digoxin (0.125 mg/day in two patients and 0.250 mg/day in 17 patients), the 24-hour mean heart rate derived from ambulatory ECG recording was reduced by 16.3% in comparison with digoxin therapy alone; the serum digoxin level was not significantly changed (1.06 +/- 0.43 vs 1.05 +/- 0.61 ng/ml). After a standardized bicycle exercise test (50 watts for 3 minutes), maximal heart rate was reduced by 19.9%, diastolic blood pressure was decreased by 8.9%, and systolic pressure-rate product was decreased by 12.5%. Diltiazem plasma levels (mean 120.9 +/- 63.3 ng/ml) were linearly correlated with percentage variations in maximal heart rate, diastolic blood pressure, systolic blood pressure, and pressure-rate product during exercise. Eighteen patients in succession discontinued digoxin therapy; after 14 days of diltiazem alone, the 24-hour mean heart rate returned to control values of digoxin therapy, whereas maximal heart rate and pressure-rate product during exercise were significantly reduced (-17.2% and -14.1%, respectively), with no changes in blood pressure. Diltiazem plasma levels (135.0 +/- 83.2 ng/ml) showed a linear correlation with the percentage of reduction in maximal heart rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Antispasmodic effect of amiodarone on gastrointestinal smooth muscle: possible involvement of calcium.

The influence of amiodarone on contractions induced by acetylcholine (ACh) was studied in isolated preparations of guinea-pig ileum, duodenum and stomach fundus as well as in rat stomach fundus. In the guinea-pig ileum a concentration-dependent antispasmodic effect of amiodarone (20-70 microM) was observed after 30 min exposure to the drug, but not after 15 min. The inhibition of ACh-induced contraction further increased with time after removal of amiodarone from the bathing fluid. Similar results were obtained in ileum preparations maintained in a low Ca2+ medium (0.35 mM CaCl2) and under these conditions the response to ACh was restored by washing the tissue with a normal Ca2+ medium (1.4 mM CaCl2). Both low Ca2+ and amiodarone depressed the tonic component of ACh-induced contraction more than the phasic one. Guinea-pig duodenum was more susceptible than the ileum to the antispasmodic action of amiodarone and again this effect was slow in onset and not reversible. The highest inhibition of ACh-induced contractions by amiodarone was obtained in guinea-pig stomach fundus. In these preparations treated with a low amiodarone concentration (20 microM) the response to ACh was restored after drug removal. In rat stomach fundus the effect of amiodarone was low and not reversible. Like amiodarone, Ca2+ lowering caused a decrease in the response to ACh with the following order of effectiveness: guinea-pig stomach greater than guinea-pig duodenum greater than guinea-pig ileum greater than rat stomach. The inhibitions caused by amiodarone and by low Ca2+ were always additive. These results indicate that amiodarone exerts an antispasmodic effect on the gastrointestinal tract and that regional and species differences exist for this action. The possible involvement of Ca2+ in this effect is discussed.