Post-prandial decrease in plasma growth hormone levels is not related to the increase in plasma insulin levels in goats

Objective: In the present study, we examined whether the post-prandial reduction in plasma growth hormone (GH) levels is related to the increase in plasma insulin levels in ruminants. Methods: We performed two experiments: intravenous bolus injection of insulin (0.2 IU/kg body weight) or glucose (1.0 mmol/kg body weight) was administered to increase the plasma insulin levels in male Shiba goats. Results: In the insulin injection experiment, significant (p<0.05) increase in GH concentrations was observed, 15 to 20 min after the injection; it was accompanied with a significant (p<0.01) increase in cortisol concentrations at 45 to 90 min, when compared to the concentrations in the saline-injected controls. The glucose injection significantly (p<0.05) increased the plasma GH concentration at 20 to 45 min; this was not accompanied by significantly higher cortisol concentrations than were observed for the saline-injected control. Hypoglycemia induced by the insulin injection, which causes the excitation of the adrenal cortex, might be involved in the increase in insulin levels. Conclusion: Based on these results, we conclude that post-prandial increases in plasma insulin or glucose levels do not induce a decrease in GH concentration after feeding in the ruminants.