Plasma growth hormone, somatostatin, insulin and glucagon inter-relationships during infusion of human pancreatic growth hormone-releasing factor in young and adult ducks (Anas platyrhynchos)

Circulating levels of insulin and avian pancreatic polypeptide in pigeons under different experimental conditions

Changes in circulating levels of insulin and avian pancreatic polypeptide (APP) were studied in pigeons under different experimental conditions. Anesthetized pigeons in which the pectoralis muscles were stimulated electrically for periods of 1 or 5 hr showed significant reduction in plasma insulin levels but not in APP levels. Cold exposure (-15 degrees, 90 min) of fully feathered (FF) or partially (dorsum and breast) defeathered (PD) pigeons produced no significant changes in plasma levels of insulin or APP. Heat exposure (+45 degrees, 90 min) of FF and PD pigeons caused no change in plasma levels of insulin; however, APP levels were significantly increased. In pigeons subjected to bilateral cervical vagotomy, there was no change in the level of plasma insulin but APP levels were found to be significantly increased.

Thyrotrophin-releasing hormone-induced growth hormone secretion in ducks: independence of peripheral plasma somatostatin, insulin, and glucagon

In young, but not old, ducks the iv infusion of thyrotrophin-releasing hormone (TRH) markedly increased peripheral plasma growth hormone (GH) concentrations, which remained elevated throughout the 30-min period of infusion. This GH response to TRH was suppressed by the simultaneous infusion of somatostatin, which increased the level of circulating somatostatin-like immunoreactivity (SLI) to supraphysiological levels. Basal concentrations of plasma SLI in both young and old birds were suppressed by TRH infusion. Concentrations of glucagon-like immunoreactivity (GLI) were increased by the infusion of TRH in young birds but not in adults, whereas plasma immunoreactive insulin (IRI) was decreased in young birds and increased in adults following TRH infusion. These results indicate that TRH-induced GH secretion in ducks is unrelated to changes in peripheral plasma SLI, GLI, or IRI induced by TRH infusion.