Effect of intravenous injection of progesterone and its co-administration with growth hormone and morphine on ghrelin concentration in ewes with food restriction

Introduction: Ghrelin increases growth hormone secretion and food intake. Growth hormone (GH), steroid hormones and opioids are involved in the regulation of food intake. So, they may have a role in the regulation of ghrelin secretion. We determined the effect of intravenous injections of progesterone, GH and morphine or co-administration of these hormones on ghrelin concentration and body weight in sheep with food deprivation. Methods: Ten sheep (weighing 30-35 kg) were randomly divided into 2 groups that received either 50% or 100% of their diet for 10 days. Both groups on days 7, 8, 9 and 10 received progesterone (1mg), simultaneous injection of progesterone (1mg) and GH (0.01mg), simultaneous injection of progesterone (1mg) and morphine (1mg) or coadministration of progesterone (1mg), GH (0.01mg) and morphine (1mg) via jugular vein, respectively. Blood samples were taken before injection and 2 h after injection via jugular vein. Body weight was measured on first, 7th and 10th days of experiment. Serum ghrelin concentration was measured by RIA. Results: Results showed that food deprivation increased ghrelin concentration. Also, intravenous injection of progesterone reduced ghrelin concentration in sheep and this reduction was significant in ad libitum (P<0.05). Simultaneous injection of progesterone and GH, simultaneous injection of progesterone and morphine or coadministration of progesterone, GH and morphine significantly increased ghrelin concentration in both groups (P<0.05). Conclusion: Progesterone-induced increase in appetite is not due to ghrelin. Injection of progesterone (1mg) decreased ghrelin concentration, but simultaneous injection of progesterone (1mg) and growth hormone (0.01mg) increased it.