Is there an extrapancreatic source of insulin in aves?
The possibility of an extrapancreatic source of insulin in birds was investigated by an examination of the action of tolbutamide, an insulin-releasing agent, in two types of depancreatized chicken. Changes in plasma glucose and immunoreactive insulin levels were studied: in response to partial (99%) pancreatectomy; in response to multiple injections of tolbutamide into partially depancreatized (99%) chickens; in response to "total" pancreatectomy; and in response to tolbutamide injections into "totally" depancreatized chickens. The tissue response of remnant pancreatic tissue to partial pancreatectomy also was examined. The results of this study indicate that partial (99%) pancreatectomy in the chicken causes only transitory disturbances in plasma glucose and insulin levels, both of which are rapidly repaired. Tolbutamide elicits an hypoglycemic response in normal and in depancreatized chickens via release of insulin from a secretory source. Carboxytolbutamide was found to decrease circulating insulin levels although it had no detectable effect on plasma glucose levels. Although remnant pancreatic tissue (the splenic lobe of the pancreas) was shown to increase in size following partial pancreatectomy, removal of this remnant in a second-stage operation ("total" pancreatectomy) neither abolished plasma insulin levels nor prevented the characteristic hypoglycemic response to injected tolbutamide. The evidence presented herein suggests the presence of an unidentified extrapancreatic (or accessory) source of insulin in the chicken.