Effectiveness of somatostatin in regulating pancreatic splenic lobe hormone secretion following 99% pancreatectomy in adult chickens.

In vivo studies were carried out in adult chickens in an attempt to evaluate the effectiveness of somatostatin (SRIF) in regulating hormone secretion from the splenic pancreatic lobe after 99% of the pancreatic mass was surgically ablated. Sixteen days after either sham operation or 99% pancreatectomy, birds were infused iv with SRIF (420 ng/min) alone and then glucose (59 mg/Kg/min) was superimposed on the infusate, or birds were infused iv with glucose alone and then SRIF was superimposed on the infusate. Serial blood samples were taken during the 16-day postoperative period and also at regular intervals during the 75-min observation period. Plasma was analyzed for glucose, insulin (IRI), glucagon (IRG), pancreatic polypeptide (IRAPP), and somatostatin (IRSRIF). Careful standardization of the SRIF radioimmunoassay, as well as analysis of the molecular form of circulating SRIF, indicated that "true" SRIF levels were being estimated in plasma of both groups of chickens. Normal-fed chickens have plasma SRIF levels of 1.12 +/- 0.07 ng/ml which increases 16 days after 99% pancreatectomy to 2.39 +/- 0.15 ng/ml plasma. The latter decreases by 55% with an overnight fast. Glucose infusion, superimposed upon a preexisting SRIF infusion in adult chickens, did not evoke an IRI response in the 99% depancreatized birds equal to that observed in sham-op controls. Although a full SRIF dose-response curve was not generated, the glucose data strongly suggest a reduced sensitivity of insulin-secreting cells to SRIF in pancreoprivic birds. Both bird groups were equally--and markedly--sensitive to the IRG-depressant effects of SRIF; in contrast, the depancreatized chickens were significantly more resistant to the APP-inhibitory effects of SRIF when compared to the sham-op control birds. Thus, 16 days after partial pancreatectomy, the hormone-release mechanisms appeared altered for IRI and IRAPP in response to SRIF. Data obtained when glucose infusions preceded SRIF infusions indicated that A-cell release of glucagon was much more sensitive to glucose (as a depression) in the partially depancreatized birds than in control birds. These same birds were significantly less responsive to the glucose-depressant effect on plasma APP levels. Thus, it appears that 99% pancreatectomy increases the sensitivity of the SRIF, IRI, and IRG release mechanisms in response to glucose 16 days after surgery. The insulin-to-glucagon (I/G) molar ratios indicative of metabolic anabolism can still be achieved by nutrients 16 days after partial pancreatectomy.(ABSTRACT TRUNCATED AT 400 WORDS)