Somatostatin Receptor Type 2 (SSTR2) Antagonism and Hypoglycemia in Diabetes

Hypoglycemia is one of the most serious acute complications in intensively treated diabetes. Recurrent hypoglycemia predisposes individuals to subsequent hypoglycemia, and diminished counterregulatory hormone responses increase this threat. Elevated pancreatic and/or circulating somatostatin has been reported in diabetic humans and animals, and we postulated that excessive somatostatin contributes to the attenuation of counterregulatory hormone release during hypoglycemia in diabetes. It is known that somatostatin suppresses stimulated secretion of glucagon, epinephrine, and corticosterone. We hypothesized that selective somatostatin receptor type 2 (SSTR2) antagonism would: (Study 1) improve hormone counterregulation to hypoglycemia, and (Study 2) ameliorate hypoglycemia in recurrently hypoglycemic rats. Using both high (10 U/kg) and low (5 U/kg) dose insulin to induce hypoglycemia, we demonstrate that inhibiting the action of somatostatin on SSTR2 normalizes the severely attenuated glucagon and corticosterone responses to acute hypoglycemia in diabetic rats. These improvements were specific to diabetes since SSTR2 antagonism did not increase these hormones in non-diabetic rats in response to hypoglycemia. In the absence of hypoglycemia, SSTR2 antagonist neither markedly alters glycemia nor causes sustained elevations in counterregulatory hormones in diabetic animals. Diabetic rats exhibit up to 65% and 75% more pancreatic and plasma somatostatin than non-diabetic rats following hypoglycemia, respectively. Despite improvements of glucagon and corticosterone, expression of gluconeogenic enzymes PEPCK1 and G6Pase was unaltered. SSTR2 antagonism reduced the glucose requirement during a hypoglycemic clamp induced with a lower dose of insulin. In recurrently hypoglycemic diabetic rats, we demonstrate that SSTR2 antagonist treatment reduces the depth and duration of hypoglycemia and promotes the recovery to euglycemia, without affecting the glycemia-lowering effect of insulin. This amelioration of hypoglycemia by SSTR2 antagonism may be attributable in part to the observed modest improvements of glucagon, epinephrine, and corticosterone counterregulation following recurrent hypoglycemia. These results implicate an important role for increased pancreatic, and possibly circulating, somatostatin in defective hypoglycemic counterregulation in diabetes.