Effect of a somatostatin infusion on circulating levels of adipokines in obese women.

OBJECTIVE: Changes in circulating levels of many adipocyte-derived peptides, including adipokines such as adiponectin, leptin and tumor necrosis factor alpha (TNF-α), have been reported in obesity (OB). Somatostatin (SRIF) inhibits circulating levels of adiponectin and leptin in lean (LN) subjects, but the effect of a SRIF infusion on these adipokines, including TNF-α, in OB is to date unknown. METHODS: Ten young women (5 OB and 5 LN) were studied. All subjects underwent an infusion of SRIF (9 µg/kg/h i.v., over 60 min), with blood samples drawn prior to and at different time intervals after SRIF administration. Plasma levels of adiponectin, leptin and TNF-α were measured at each interval. RESULTS: Basal levels of leptin and TNF-α were significantly higher in OB than LN women, whereas levels of adiponectin were significantly lower in OB than LN subjects. SRIF significantly inhibited plasma concentrations of adiponectin (at 60 min) in both OB and LN women, without affecting those of leptin and TNF-α in either group. In LN subjects, the inhibitory effect of SRIF on plasma adiponectin persisted up to 150 min, whereas SRIF infusion withdrawal in OB women resulted in a prompt restoration of basal levels of the adipokine. CONCLUSIONS: Plasma concentrations of leptin and TNF-α, which are higher in OB than LN subjects, are unaffected by a SRIF infusion, which, in contrast, inhibits circulating levels of adiponectin in both groups, with a delayed return to the baseline secretion of the adipokine in LN subjects.

Effect of somatostatin infusion on peptide YY secretion: studies in the acute and recovery phase of anorexia nervosa and in obesity.

OBJECTIVE: Changes in many gastrointestinal peptides, including the anorexigenic peptide YY (PYY), which is produced by L cells, occur in both anorexia nervosa (AN) and obesity (OB). High PYY levels are present in AN, whereas in morbid OB fasting and postprandial PYY secretion is blunted. Somatostatin (somatotropin release-inhibiting factor (SRIF)) reportedly inhibits plasma PYY concentrations in animals and healthy humans, but the effect of a SRIF infusion on spontaneous PYY secretion in AN and OB is unknown. METHODS: A total of 18 young women, seven with acute AN (A-AN), four with AN in the recovery phase (R-AN), and seven with morbid OB, were studied. All subjects underwent an infusion of SRIF (9 µg/kg i.v./h, over 60 min), with blood samples drawn before and at different time intervals after SRIF administration. Plasma PYY levels were measured at each time point. RESULTS: SRIF significantly inhibited plasma PYY concentrations in R-AN and OB, without affecting PYY titers in A-AN. In OB, the inhibitory effect of SRIF also persisted at 90 min. Withdrawal of SRIF infusion in R-AN resulted in a prompt restoration of basal plasma PYY levels, whereas termination of SRIF infusion in OB was followed by a slower increase of PYY titers toward baseline levels. After infusion, PYY Δ area under the curve (ΔAUC) in R-AN was significantly higher than those in A-AN and OB patients. A significant difference in PYY ΔAUC between A-AN and OB was present. CONCLUSIONS: These results suggest the existence of a hypo- and hyper-sensitivity of L cells to the inhibitory effect of SRIF in A-AN and OB respectively.

Children with Prader-Willi syndrome exhibit more evident meal-induced responses in plasma ghrelin and peptide YY levels than obese and lean children.

BACKGROUND AND AIMS: Ghrelin is an orexigenic 28-amino acid peptide produced by the stomach. Circulating ghrelin levels rise shortly before and fall shortly after every meal. Peptide YY (PYY), an anorexigenic 36-amino acid peptide, is secreted primarily from the intestinal mucosa of the ileum and large intestine. Plasma PYY levels begin to rise within 15 min after starting to eat and plateau within approximately 90 min, remaining elevated for up to 6 h. Recently, some studies have tried to evaluate the potential role of ghrelin and PYY in the hyperphagia of patients with Prader-Willi syndrome (PWS). While hyperghrelinemia is well characterized in PWS, conflicting results have been reported for PYY. The aim of the study was to investigate ghrelin and PYY responses to a standard liquid high-fat meal in children with PWS. PATIENTS AND METHODS: Circulating levels of total ghrelin and PYY levels were assayed by RIA after overnight fasting and 45, 60, 90, and 180 min following a standard meal (Ensure 6 ml/kg) in 16 patients with PWS (11 boys and five girls, aged 4.6-10.7 years, including ten receiving 0.02 mg/kg per day rhGH for 2-18 months; body mass index (BMI) z-score: 0.6+/-0.2 and 1.6+/-0.5 for children treated or not treated with rhGH respectively), ten obese (eight boys and two girls, aged 9.2-15.6 years; BMI z-score: 2.4+/-0.2, i.e. BMI >97th centile for chronological age and sex) subjects, and 16 normal-weight controls (five boys and 11 girls, aged 5.8-17.3 years; BMI z-score: 0.6+/-0.2). RESULTS: PWS children showed higher fasting levels of ghrelin than obese and lean controls. Postprandial ghrelin drop was more pronounced in PWS than in the other study groups. No significant difference on fasting levels of PYY was found among groups. PWS showed a higher postprandial PYY rise than obese and lean controls. PWS patients treated and not treated with GH showed similar fasting and postprandial levels of ghrelin and PYY. Fasting PYY levels correlated negatively (P<0.05; r=-0.68) with those of ghrelin only in PWS. CONCLUSIONS: The results of this study confirm fasting hyperghrelinemia in PWS. Since in PWS adults an impaired postprandial suppression of plasma ghrelin was previously reported to be associated with a blunted postprandial PYY response, the finding of a meal-induced decrease and increase in ghrelin and PYY levels respectively in PWS children would imply that the regulation of appetite/satiety of these peptides is operative during childhood, and it progressively deteriorates and vanishes in adulthood when hyperphagia and obesity worsen.

Combined evaluation of resting IGF1, N-terminal propeptide of type III procollagen and C-terminal cross-linked telopeptide of type I collagen levels might be useful for detecting inappropriate GH administration in female athletes.

OBJECTIVE: To detect exogenous recombinant human GH (rhGH) abuse in female athletes. DESIGN: GH-dependent markers were assayed in serum of 100 female athletes (control group) and in a subgroup of nine female subjects treated with rhGH (0.09 IU/kg body weight, 6 days/week for 3 weeks). METHODS: Cut-off values (mean+2 s.d.) for IGF1, N-terminal propeptide of type III procollagen (PIIINP) and C-terminal telopeptide of type I collagen (ICTP) were calculated and arbitrary scores (1.5 or 2.0) were assigned to abnormal markers. By using the sum of individual marker scores, positive (> or =3) or negative (<3) scores were obtained. RESULTS: None of the control group obtained a positive score (> or =3). Abnormal IGF1, PIIINP and ICTP levels were found in 61.4, 54.5 and 11.4% samples of the treated group. Overall, positive cases were present in 43.2% blood samples drawn in subjects treated with rhGH and in 26% of samples after rhGH withdrawal. The sensitivity of the detection approach was 66.6% at the end of 3-week rhGH treatment and 11.1% at the 15th day of rhGH withdrawal, while the specificity was 100%. CONCLUSION: Detection test for rhGH administration appears less sensitive in female (66.6%) than in male athletes (previous observation, 100% after 3 weeks of comparable rhGH dose), but shows a similar specificity (98.5-100%). Since athletes supposedly use very high doses and long-term administration of rhGH for doping purposes, it is foreseen that the here-in detection test would in future increase its strength.

Chronic intracerebroventricular injection of TLQP-21 prevents high fat diet induced weight gain in fast weight-gaining mice.

The vgf gene regulates energy homeostasis and the VGF-derived peptide TLQP-21 centrally exerts catabolic effects in mice and hamsters. Here, we investigate the effect of chronic intracerebroventricular (icv) injection of TLQP-21 in mice fed high fat diet (HFD). Fast weight-gaining mice injected with the peptide or cerebrospinal fluid were selected for physiological, endocrine, and molecular analysis. TLQP-21 selectively inhibited the increase in body weight and epididymal white adipose tissue (eWAT) weight induced by HFD in control animals despite both groups having a similar degree of hyperphagia. TLQP-21 normalized the increase in leptin and decrease in ghrelin while increasing epinephrine and epinephrine/norepinephrine ratio when compared to values in controls. Finally, HFD-TLQP-21 mice showed a selective increase of eWAT beta3-adrenergic receptor mRNA. Peroxisome-proliferator-activated-receptor-delta and hormone-sensing-lipase mRNA were also upregulated. In conclusion, chronic icv infusion of TLQP-21 prevented the early phase of diet-induced obesity despite overfeeding. These effects were paralleled by activation of catabolic pathways within the eWAT. Our results further support a role for TLQP-21 as a catabolic neuropeptide.

Asymmetric dimethylarginine (ADMA) induces vascular endothelium impairment and aggravates post-ischemic ventricular dysfunction in rats.

Asymmetric dimethylarginine (ADMA) is an endogenous nitric oxide (NO) inhibitor recognized as an independent risk factor for endothelial dysfunction and coronary heart diseases. This study investigated whether ADMA (10 mg/kg day for 14 days) affected endothelial function and aggravated post-ischemic ventricular dysfunction in the perfused rat heart. Systolic blood pressure and heart rate, plasma levels of ADMA and nitrite/nitrate were measured in vehicle- and ADMA-treated rats. Perfused hearts were submitted to global ischemia-reperfusion and vascular endothelial dysfunction was examined with angiotensin II in coronary vessels and aortic rings. Endothelial NO synthase (eNOS) and angiotensin-converting enzyme (ACE) mRNA expression in aortic and cardiac tissues were measured. ADMA-treated rats had higher systolic blood pressure (1.3-fold, P<0.01) and slower heart rate (16%, P<0.05) than controls. Plasma ADMA rose (1.9-fold, P<0.01) and nitrite/nitrate concentration decreased 59% (P<0.001). Ventricular contraction (stiffness) increased significantly, with worsening of post-ischemic ventricular dysfunction. In preparations from ADMA-treated rats the coronary vasculature's response to angiotensin II was almost doubled (P<0.01) and the maximal vasorelaxant effect of acetylcholine in aortic rings was significantly lower than in preparations from vehicle-treated rats. In cardiac and aortic tissues eNOS mRNA and ACE mRNA levels were similar in controls and ADMA-treated rats. The increased plasma levels of ADMA presumably cause endothelial dysfunction because of a deficiency in NO production, which also appears involved in the aggravation of myocardial ischemia-reperfusion injury.

Early tolerance to the hypophagic effect of the cannabinoid receptor antagonist SR141716 does not impede blockade of an orexigenic stimulus.

The cannabinoid CB1 receptor antagonist SR141716 (Rimonabant) is known to reduce food intake by central and peripheral mechanisms. Recently, SR141716 has been reported to block the orexigenic effect of ghrelin, a potent orexigenic peptide produced by the stomach. This study investigated whether in rats, made tolerant to the hypophagic effect of SR141716, the drug was still capable to block the orexigenic activity of another non-natural (hypothalamic) peptide, i.e., the growth hormone releasing peptide (GHRP) hexarelin, a ghrelin mimetic. In the acute experiments, each dose of SR141716 (1, 5 and 10 mg/kg i.p.) reduced food intake with respect to vehicle-treated rats, whereas hexarelin (160 microg/kg s.c.) markedly stimulated feeding. All doses of SR141716 were capable to reduce the orexigenic effect of the GHRP. A 15-day administration of SR141716 (10 mg/kg i.p.) reduced both food intake and body weight. Tolerance to the hypophagic effect of SR141716 developed within 5 days, but in contrast, body weight remained markedly below that of vehicle-treated group throughout the entire treatment period. Interestingly, despite development of tolerance to its hypophagic effect, SR141716 was capable to suppress the orexigenic effect of repeated hexarelin challenge tests performed throughout the chronic experiments. In conclusion, the results of the present study confirm and broaden the existence of a functional relationship between ghrelin and endocannabinoids in the control of food intake, and bespeak the ability of a CB1 receptor antagonist to suppress orexia caused by stimuli alien to direct stimulation of the cannabinoid system.

Orexigenic effects of a growth hormone secretagogue and nitric oxide in aged rats and dogs: correlation with the hypothalamic expression of some neuropeptidergic/receptorial effectors mediating food intake.

Hypothalamic neurochemical alterations in mammals underlie disturbances of food intake. There is scarce information on these topics in elderly persons; therefore, the aims of the present study were: (i) to evaluate the orexigenic effects of a growth hormone secretagogue, administered to young and old rats and dogs, alone or in combination with molsidomine, a donor of nitric oxide and (ii) to evaluate by reverse transcription-polymerase chain reaction in the whole hypothalamus of young and old rats messenger RNA levels of a wide number of anabolic and catabolic peptides, receptors, and enzymes involved in the control of feeding behavior, relating the detected titers, whenever possible, to the feeding responses to growth hormone secretagogue. In all, the results obtained strengthen the proposition that, in the hypothalamus of old rats, anti-anorexigenic compensatory mechanisms are operative, aimed at maintaining a "normal" feeding pattern. Thus, the occurrence of a primary, age-related alteration in the feeding mechanisms is unlikely.

Angiotensin II type 1 receptor antagonism improves endothelial vasodilator function in L-NAME-induced hypertensive rats by a kinin-dependent mechanism.

OBJECTIVE: This study was designed to investigate the ability of a chronic blockade of angiotensin II type 1 receptors with losartan to reverse the endothelial dysfunction present in N-nitro-L-arginine methyl ester (L-NAME)-treated hypertensive rats and the possible dependence of this effect on bradykinin B2-receptor activation. METHODS: Rats treated with L-NAME alone (60 mg/kg per day for 8 weeks) or with L-NAME + losartan, L-NAME + icatibant (a bradykinin B2-receptor antagonist) and L-NAME + losartan + icatibant were studied. Losartan, icatibant or losartan + icatibant were co-administered with L-NAME during the last 4 weeks of the experiment. Endothelial nitric oxide synthase gene expression in aortic tissues, plasma nitrite/nitrate concentrations, the relaxant effect of acetylcholine on norepinephrine-precontracted aortic rings and 6-keto-PGF1alpha release from aortic rings were used as markers of the endothelial function. RESULTS: Rats treated with L-NAME alone and L-NAME + icatibant showed, as compared with untreated animals, a clear-cut increase in systolic blood pressure and a decrease of all the markers of endothelial function evaluated. In L-NAME-rats, administration of losartan reduced the systolic blood pressure and restored endothelial nitric oxide synthase gene expression, plasma nitrite/nitrate levels, the relaxant activity of acetylcholine on aortic rings and the generation of 6-keto-PGF1alpha from the aortic tissues. Co-administration of icatibant with losartan blunted the stimulatory effect of losartan on the markers of endothelial function evaluated. CONCLUSION: These results demonstrated that losartan is capable of reversing the endothelial vasodilator dysfunction in L-NAME-induced hypertensive rats, and that the beneficial effect of losartan is mediated by bradykinin B2-receptor activation.

Angiotensin-converting enzyme inhibition and angiotensin AT1-receptor antagonism equally improve endothelial vasodilator function in L-NAME-induced hypertensive rats.

Male Sprague-Dawley rats given N(omega)-nitro-L-arginine methyl ester (L-NAME) in drinking water for 8 weeks showed: (1) a clear-cut increase in systolic blood pressure; (2) a consistent decrease of endothelial-cell nitric oxide synthase (eNOS) gene expression in aortic tissue; (3) a marked reduction of plasma nitrite/nitrate concentrations; (4) a reduction of the relaxant activity of acetylcholine (ACh, from 10(-10) to 10(-4) M) on norepinephrine-precontracted aortic rings (reduction by 48+/-5%); (5) a marked decrease (-58%) of the basal release of 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha) from aortic rings. In L-NAME-treated rats, administration in the last 4 weeks of either the angiotensin-converting enzyme (ACE) inhibitor enalapril (10 mg/kg/day in tap water) or the angiotensin AT(1)-receptor antagonist losartan (10 mg/kg/day in tap water) decreased systolic blood pressure levels, completely restored eNOS mRNA levels in aortic tissue and plasma nitrite/nitrate levels, and allowed a consistent recovery of both the relaxant activity of acetylcholine and the generation of 6-keto-PGF1alpha. Coadministration of icatibant, a bradykinin B(2)-receptor antagonist (200 microg/kg/day), with enalapril blunted the stimulatory effect of the ACE inhibitor on eNOS mRNA expression, circulating levels of nitrite/nitrate, the relaxant activity of ACh and the release of 6-keto-PGF1alpha in L-NAME-treated rats. The generation of 6-keto-PGF1alpha from aortic rings was also decreased in rats coadministered icatibant with losartan. These findings indicate that (1) the ACE inhibitor enalapril and the angiotensin AT(1)-receptor blocker losartan are equally effective to reverse NAME-induced endothelial dysfunction; (2) the beneficial effect of enalapril on the endothelial vasodilator function in L-NAME-treated rats is mediated by bradykinin B(2)-receptor activation; and (3) the enhanced endothelial generation of prostacyclin induced by losartan in L-NAME rats is also mediated by bradykinin B(2)-receptor activation.

Investigation of peptide YY and ghrelin responses to a test meal in bulimia nervosa.

BACKGROUND: Gut-derived peptides, such as peptide YY (PYY) and ghrelin that regulate the initiation and termination of meals, could play a role in the altered eating behavior of patients with bulimia nervosa (BN). Therefore, we aimed to assess plasma PYY and ghrelin responses to a test meal in symptomatic bulimics. METHODS: Ten healthy women and nine women with BN underwent blood sample collections before and after the ingestion of a test meal of 1300 Kcal (with 15% carbohydrates, 10% proteins, and 75% fat) at 12:00 noon. Plasma total PYY, ghrelin, insulin, and glucose were assayed. RESULTS: As compared with healthy women, bulimics exhibited a significantly blunted increase of circulating PYY (p < .007) and a significantly reduced suppression of plasma ghrelin (p < .0004) after the test meal. No significant differences emerged in food-induced plasma insulin and glucose changes between the two groups. Plasma ghrelin suppression after the meal was significantly correlated with plasma PYY increase. CONCLUSIONS: We replicated our previous findings of an altered ghrelin response to food ingestion in people with BN and showed for the first time a blunted PYY increase after food consumption in these patients. These findings support the occurrence in BN of a profound dysregulation of some peripheral regulatory mechanisms involved in the short-term regulation of feeding behavior that might be involved in the pathophysiology of their binge eating behavior.

Growth hormone abuse: methods of detection.

In the past two decades, growth hormone (GH) has been considered as a performance-enhancing drug in the sport world, certainly favoured by the awareness that there is not yet an approved method for detecting its abuse. Because resting or random measurements of plasma GH concentrations per se are meaningless, new methods have been devised to evaluate plasma levels of GH-sensitive substances that are more stable, and hence detectable, than the hormone itself. This review discusses some of the most recently proposed approaches, including a diagnostic algorithm, based on the timed application of different tests, which, collectively, would have a high diagnostic capability.

The nitric oxide donor molsidomine antagonizes age-related memory deficits in the rat.

The effects of the nitric oxide (NO) donor molsidomine on aged rats' cognition were evaluated in two different behavioral tasks: the step-through passive avoidance paradigm and the object recognition test. Post-training injection of molsidomine (at 4 but not at 2 mg/kg) significantly counteracted the performance deficits displayed by old rats in both the behavioral paradigms. These results support and extend prior findings about the implication of NO in learning and memory mechanisms. In addition, for the first time, a NO donor was found to antagonize age-related memory impairments, suggesting that the integrity of the NO-ergic system may be important in brain aging processes.

Age and secretagogue type jointly determine dynamic growth hormone responses to exogenous insulin-like growth factor-negative feedback in healthy men.

The primary cause of waning GH and IGF-I concentrations in healthy aging adults is not established. To test the postulate that age influences negative feedback by IGF-I in a secretagogue-specific fashion, 17 normal men (nine young and eight older) each completed eight randomly ordered injections of placebo or recombinant human (rh) IGF-I (20 microg/kg sc), followed by saline/rest, aerobic exercise, GHRH (1 microg/kg iv bolus), or GH-releasing peptide-2 (1 microg/kg iv bolus) stimulation. GH secretion was monitored by sampling blood every 10 min for 7 h, high-sensitivity immunochemiluminometric assay, and deconvolution analysis conditioned on prior pulse-onset times and biexponential kinetics. Analysis of covariance showed that age (P = 0.028), secretagogue (P < 0.001), and rhIGF-I (P < 0.005) individually determine pulsatile GH secretion and exhibit a strong 3-fold interaction (P < 10(-5)). Post hoc comparisons revealed that elderly subjects manifest less IGF-I inhibition of a maximal GHRH stimulus (P = 0.013 vs. young), blunted initial IGF-I suppression of fasting GH release (P = 0.038), and impaired IGF-I feedback on the regularity of GH secretion (P = 0.023). Age stratum did not influence peak IGF-I and nadir GH concentrations or rhIGF-I-induced inhibition of GH secretion stimulated by exercise or GH-releasing peptide-2. In summary, experimental elevation of IGF-I concentrations unmasks reduced rhIGF-I-dependent feedback inhibition of fasting and GHRH-stimulated GH secretion in healthy older men, indicating that aging selectively modulates the autoinhibition process.

Combined evaluation of resting IGF-I, N-terminal propeptide of type III procollagen (PIIINP) and C-terminal cross-linked telopeptide of type I collagen (ICTP) levels might be useful for detecting inappropriate GH administration in athletes: a preliminary report.

OBJECTIVE: To verify whether combined measurements of GH-dependent parameters might be useful in detecting exogenous recombinant GH (rGH) administration in male athletes from different disciplines. METHODS: Sixty-six athletes (control group) were sampled for the evaluation of resting IGF-I, N-terminal propeptide of type III procollagen (PIIINP) and telopeptide type I collagen (ICTP). Cut-off values (mean + 2 SD) for IGF-I, PIIINP and ICTP were calculated and arbitrary scores (1.5, 2.0) were assigned to abnormal parameters. By using the sum of individual parameter scores, positive (> or = 3) or negative (< 3) scores were obtained. In addition, a subgroup of six athletes was treated for 3 weeks with rGH (0.09 IU/kg body weight, 6 days/week) and was similarly evaluated at the end of the 1st, 2nd and 3rd week (i.e. 18 samples). RESULTS: Abnormal IGF-I, or PIIINP or ICTP levels were found, respectively, in one, two and four subjects (1.5-6.1%) of the control group (in the younger athletes); only one 19-year-old subject of this group obtained a positive score. Abnormal IGF-I, PIIINP and ICTP levels were found in 61.1-66.7% samples of the treated group. Positive cases were 3/6 at the 1st and 2nd week and 6/6 at the 3rd week. The sensitivity of the screening approach was 50-100% (at the 1st-2nd and 3rd week, respectively) and specificity was 98.5%. CONCLUSION: This 'first level' screening test is safe, acceptable and relatively inexpensive. Further additional investigations of 'second level' (i.e. GH secretory profile, GH response to a GH-releasing peptide) can be retained to validate or exclude rGH administration or for the early diagnosis of infrequent endogenous GH hypersecretion.

Hexarelin modulates the expression of growth hormone secretagogue receptor type 1a mRNA at hypothalamic and pituitary sites.

Ghrelin and the synthetic growth hormone secretagogues (GHSs) activate a G-protein-coupled receptor (GHS-R) originally cloned from the pituitary, but which is also expressed in the hypothalamus, in other areas of the brain and in numerous peripheral tissues. Several studies have shown that growth hormone (GH)-releasing hormone (GHRH) is necessary for GHSs to exert maximal GH release in vivo. The exact mechanism of this synergism is not clear. Previous data suggest that GHSs can affect pituitary GHS-R mRNA expression; however, it is unknown whether this effect is age dependent and whether hypothalamic GHS-Rs are also affected. In this study, we tested whether (a) the synthetic GHS hexarelin regulates mRNA expression of its own receptor at the pituitary and/or hypothalamus and whether this effect is age dependent, and (b) whether short-term treatment with GHRH or, conversely, passive immunization against GHRH affects pituitary GHS-R1a mRNA expression in infant (10 days old) and young adult rats. GHS-R1a mRNA expression was measured with competitive reverse transcriptase-polymerase chain reaction. Hexarelin treatment significantly increased pituitary and hypothalamic GHS-R1a mRNA levels in normal infant rats, but not in normal young adult rats. In addition, hexarelin administration also stimulated pituitary GHS-R1a mRNA in infant as well as in young adult rats passively immunized against GHRH. GHRH treatment significantly enhanced pituitary GHS-R1a mRNA expression in GHRH-deprived young adult rats, though it did not affect the basal levels of GHS-R1a mRNA in normal infant and adult rats. These data further support the hypothesis that GHRH can affect GHS-R1a expression and that hexarelin upregulates the expression of its own receptor at the pituitary as well as the hypothalamus in an age-dependent fashion.

Abuse of recombinant human growth hormone: studies in two different dog models.

The search for inappropriately high growth hormone (GH) titers in plasma has been widely used to detect GH abuse, despite many shortcomings especially related to the pulsatile nature of GH secretion. Hence, the need for new anti-doping strategies. In the present study dogs were used to evaluate the ability of recombinant human GH (rhGH) to affect canine GH (cGH) release ensuing after somatostatin (SS) infusion withdrawal (SSIW) - a purported stimulus for the release of endogenous GH-releasing hormone (GHRH) - or the cGH response to administration of a GH-releasing peptide (GHRP). In the SSIW experiments, 8 beagle dogs of either gender (4-6 years old) were given a subcutaneous bolus injection of physiological saline (0.1 ml/kg) or, alternatively, rhGH (0.2 IU/kg s.c.) 60 min before the starting a continuous infusion of SS (4 microg/kg g h i.v.) of 1.5 h duration. In the dogs given a saline bolus, SSIW was followed by a 'rebound' rise in plasma cGH levels. In contrast, in dogs which had received the bolus injection of rhGH, the cGH rise elicited by SSIW was completely abrogated. In the set of experiments with a GHRP challenge, 13 dogs of either gender (3-12 years old) received the following treatment schedule at least 15 days apart: (1) a single bolus injection of rhGH (0.2 IU/kg s.c.); (2) rhGH (0.05 IU/kg s.c.) daily for 12 days; (3) rhGH (0.2 IU/kg s.c.) on alternate days for 12 days, and (4) rhGH (0.2 IU/kg s.c.) daily for 12 days. For each treatment schedule, before treatment, during treatment (24 h from the previous rhGH injection) and 1, 5 and 10 days after treatment, all dogs received an intravenous injection of a GHRP, EP51216 (125 microg/kg). In all treatments under baseline conditions, a single injection of EP51216 elicited an abrupt rise in plasma cGH. Twenty-four hours after the injection of an acute bolus of rhGH, the C(max) and AUC(0-90) of the GHRP-stimulated cGH response were significantly lower than the baseline cGH response. Five days later, there was a trend in the C(max) and AUC(0-90) towards complete restoration of the original values. One, 5 and 10 days after the end of the daily treatment with rhGH (0.05 IU/kg s.c.), no significant changes in the GHRP-stimulated cGH responses vs. the baseline GH response were recorded. In contrast, treatment with rhGH at a dose of 0.2 IU/kg s.c., on either alternate or daily administration, markedly reduced the GHRP-stimulated cGH responses evaluated after 3 and 5 rhGH injections. One day after the last rhGH injection, the EP51216-stimulated cGH response was still significantly reduced when compared with that present under baseline conditions. Five and 10 days following termination of rhGH treatment on alternate days, no significant differences in the C(max) and AUC(0-90) of the cGH responses to EP51216 were present. Differently, following the end of daily rhGH treatment, a marked inhibition in the C(max) of the cGH response to EP51216 was still present at 1 and 5 days, though not at 10 days. In conclusion, these studies show that a single administration of rhGH can abrogate the cGH response ensuing SSIW or acute stimulation by a GHRP. The inhibitory effect of rhGH on the cGH response to GHRP is present even 5 days after termination of a short-lived treatment with rhGH at a dose (0.2 IU/kg) which, in the dog, is undoubtedly lower than that used in humans for doping purposes. Extrapolation of these preclinical results to humans may pave the way for the development of a new rhGH anti-doping test.

The 5-HT 1A receptor antagonist WAY 100635 improves rats performance in different models of amnesia evaluated by the object recognition task.

The effects of the 5-HT(1A) receptor antagonist WAY 100635 on recognition memory were investigated in two different amnestic models in the rat by using the object recognition task. WAY 100635 at 1 mg/kg, but not at 0.3 mg/kg, counteracted scopolamine-induced performance deficits in the acquisition version of this behavioral paradigm. At the same dose, WAY 100635 antagonized extinction of recognition memory in the normal rat, suggesting that it affected acquisition, storage and retrieval of information. These results support and extend prior findings that interactions between the serotonergic and cholinergic systems are relevant to cognition and indicate that WAY 100635 modulates different aspects of recognition memory.

Endogenous ghrelin is an orexigenic peptide acting in the arcuate nucleus in response to fasting.

Ghrelin, a circulating growth-hormone releasing peptide derived from stomach, stimulates food intake through neuropeptide Y (NPY) neurons of the arcuate nucleus in the hypothalamus (ARC). We examined the effect of ghrelin microinjected into the ARC and the influence of intracerebroventricular (i.c.v.) pretreatment with a GHRH or NPY receptor antagonist on ghrelin-induced food intake in free-feeding male rats. Ghrelin (0.1-1 microg) stimulated food intake in a dose-dependent manner, and this effect was reduced by 55-60% by the Y(5) NPY receptor antagonist (10 microg i.c.v.), but not by the GHRH receptor antagonist MZ-4-71 (10 microg i.c.v.). We also evaluated the effects of passive ghrelin immunoneutralization by the microinjection of anti-ghrelin immunoglobulins (IgGs) intracerebroventricularly or directly into the ARC on food intake in free-feeding and fasted male rats. i.c.v. administration of anti-ghrelin IgGs decreased cumulative food intake over 24 h, whereas microinfusion of anti-ghrelin IgGs into the ARC induced only a short-lived (2 and 6 h) effect. Collectively, these data would indicate that centrally derived ghrelin has a major role in the control of food intake in rats and, in this context, blood-born ghrelin would be effective only in relation to its ability to reach the ARC, which is devoid of blood-brain barrier.

Molsidomine antagonizes L-NAME-induced acquisition deficits in a recognition memory task in the rat.

The present study was designed to investigate the role of nitric oxide (NO) on the acquisition of a recognition memory task in the rat. For this purpose, the effects on memory exerted by pre-training administration of the NO synthase inhibitor L-NAME (N(omega)-nitro-L-arginine methyl ester) and the NO donor molsidomine (N-[ethoxycarbonyl]-3-[4-morpholinosydnomine]) were assessed by using the object recognition task, a working memory paradigm based on the differential exploration of a new and familiar object. In a first dose-response study, it was found that L-NAME (10, 30, and 60 mg kg(-1), i.p.) at 30 but not at 10 mg kg(-1) disrupted animals performance, whereas the dose of 60 mg kg(-1) induced side effects. Molsidomine (2 and 4 mg kg(-1), i.p.) at 4 but not at 2 mg kg(-1), antagonized the L-NAME-induced performance deficits. These results indicate that NO is involved in the acquisition of a recognition memory task.