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Introduction: It has been established that multiple neuroendocrine factors such as orexin operate as metabolic signals for the reproductive tract. Since the effects of testosterone and growth hormone on concentration of orexin in rams have not been studied, the goal of this study was to determine the effect of testosterone and growth hormone on mean plasma concentrations of orexin in rams fed restricted diets. Materials and Methods: Rams were randomly divided into 2 groups. Animals in first group were fed 100% of their required daily food and those in the second group were fed 50% of food fed to the first group for 10 days. Consequently, the rams in all groups received 6μg /Kg BW testosterone on days 7 and 8 and 6μg /Kg BW Testosterone and 5 μg /Kg BW growth hormone on days 9 and 10 of the experiment. Blood samples were collected from the jugular veins at -120 and +120 minutes of infusions. for orexin assay, Plasma orexin were measured by a homologous double-antibody radioimmunoassay (RIA). Results: Injection of different dosages of testosterone and combination of testosterone and growth hormone in the 50%-diet, significantly (P<0.05*) increased the mean plasma concentrations of orexin, while in the 100%-diet this had no effect. Conclusion: Results indicate that testosterone and growth hormone may increase mean concentrations of orexin in animals fed lower than their daily food requirement.

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Introduction: Orexin is a potent orexigenic agent in rodents and humans. Some research shows that orexin participates in the adaptive response to weight loss and its levels rise with dieting. On the other hand, weight loss and fasting is accompanied by increased levels of epinephrine and cortisol. In this study we investigated the effects of epinephrine (EN) and cortisol on fasting-induced orexin secretion in rats fed different levels of their energy requirements. Materials and Methods: Forty-five male wistar rats (300-350 g, 15 per group) were fed a diet containing 100%, 50% and 25% of their energy requirement for 10 days, rats were anesthetized following 48 hour prolonged fasting and then cannulated in the carotid artery for drug injection and blood sampling. Animals were divided into 3 treatment groups that received either (3 µg/Kg BW) EN, cortisol or a combination of those two (0.1 mg in 1 ml of PBS). Orexin and glucose levels were analyzed before (time 0), and 30, 60 and 120 min after injection. Results: In the 50% and 100% food restricted groups, fasting orexin levels fell after EN and the combination of EN and cortisol injection respectively (p≤0.05). In contrast, the group that had 25% food restriction showed no response to cortisol, EN or the combination of both (p>o.o5). Conclusion: These results indicate that injection of EN suppresses starvation-induced secretion of orexin in normal (100%) and starved (50%) rats, and that orexin secretion response to EN might be affected by weight loss.

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Introduction: Neuropeptide Y (NPY) neurons express growth hormone secretagogues receptor (GHSR-Ia). Fasting or ghrelin increases food intake by stimulating NPY gene expression via GHSR-Ia. D-Lys3 -GHRP-6, a ghrelin receptor antagonist, decreases food intakes and body weight. The present study aimed to investigate the molecular mechanism of the anorexigenic effect of D-Lys3 -GHRP-6 in food deprived rats. Materials and Methods: Fifteen food deprived rats (3 groups) received central injections of saline or D-Lys3 -GHRP-6 (2 or 20nmol) respectively and mean food intake was measured at one hour after injections. Mean plasma ghrelin concentration was measured by RIA, and NPY gene expression was determined by semi quantitative RT-PCR in the hypothalamus. Fifteen rats in three groups, received central injection of saline or initiations and on the D-Lys3 -GHRP-6 (2 or 20nmol) twice daily for 9 days respectively. Body weight was determined at third, 7th and 10th day of the experiment. Results: Mean plasma ghrelin concentration, mean food intake and NPY gene expression significantly increased in food deprived rats compared to fed animals. D-Lys3 –GHRP-6 (2 nmol) did not significantly change ghrelin, food intake and NPY mRNA levels, compared to the food deprived rats. However D-Lys3 –GHRP-6 (20 nmol) significantly decreased ghrelin, food intake and NPY mRNA level compared to food deprived group. Conclusion: Results showed that D-Lys3 -GHRP-6 may exert its anorexigenic effect on food intake by influencing the expression of peptides involved in the regulation of energy homeostasis, and may be suggested for the treatment of obesity.

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 Introduction: Previous studies have investigated the effects and importance of orexin and estradiol on food intake. In this study the effects of orexin on estradiol release by the ventromedial hypothalamus (satiety center) and lateral hypothalamus (feeding center) have been investi­gated. Forty adult male rats, divided to two groups, the control group (consisting of 10 rats) and an experimental group (consisting of 30 rats), were canulated in the lateral area and ventromedial nucleus steriotaxically. After two days recovery, 1,2 and 4 micrograms of orexin were injected into the lateral area and ventromedial nucleus. After two hours, tissue of the lateral area and ventromedial nucleus were removed and concentrations of estradiol and aromatase were measured by radio-immuno assay and RT-PCR, respectively. Results of RT-PCR showed that orexin-A(1,2,4 µg) augmented aromatase gene expression in the VMH and LH. 17-β estradiol measurement showed that 1, 2 and 4 µg orexin infusion increased estradiol levels significantly in VMH and LH, especially the 2 and 4 µg doses, observations suggesting that the neurons secreting estradiol exist in the VMH and LH.