Comparative effects of somatostatin-28 and somatostatin-14 on basal growth hormone release and pancreatic function in immature ducks (Anas platyrhynchos).

The 30-min infusion of somatostatin (SRIF)-14 or SRIF-28 (800 ng/kg/min) in 7- to 8-week-old ducklings reduced the basal level of plasma growth hormone (GH). The magnitude of the GH suppression induced by SRIF-14 was similar to that elicited by SRIF-28. "Rebound" GH secretion was observed 30 min after infusion, the GH concentration being elevated above the basal level. The increase in GH secretion after SRIF-14 infusion was greater than that induced by SRIF-28. Plasma insulin and free fatty acid (FFA) levels were similarly reduced after 10 and 30 min of SRIF-14 or SRIF-28 infusion. Following infusion the FFA levels returned to the pretreatment concentration, whereas the insulin concentration in both groups remained suppressed 30 min after infusion. The insulin level was still suppressed 60 min after SRIF-14 infusion, but not after SRIF-28 infusion. The infusion of SRIF-14 resulted in a marked, progressive increase in the glucagon concentration, which was reduced in birds infused with SRIF-28 and accompanied by hypoglycaemia. Following SRIF-28 infusion a "rebound" in the glucagon concentration occurred and remained elevated for at least 60 min. These results demonstrate comparative effects of SRIF-14 and SRIF-28 on the basal release of pituitary GH and pancreatic insulin and glucagon, and in particular they suggest that SRIF-28 is more potent in inhibiting pancreatic A cell activity.