by Joseph Jao Yiu Sung. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (p. 201-220). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Mode of access: World Wide Web.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

published_or_final_version / Physiology / Master / Master of Philosophy

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

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.

Impaired counterregulation during hypoglycemia in type 1 diabetes (T1D) is partly due to inadequate pancreatic islet alpha-cell glucagon secretion. We hypothesized that hypoglycemia can be prevented in autoimmune T1D by selective somatostatin receptor type 2 (SSTR2) antagonism of alpha cells to relieve SSTR2 inhibition, thereby increasing glucagon secretion. Diabetic biobreeding diabetes prone (BBDP) rats (D) vs non-diabetic BBDP (N) rats, underwent infusion of vehicle or SSTR2 antagonist (SSTR2a) during insulin-induced hypoglycaemia. D rats, treated with SSTR2a, needed little or no glucose to maintain hypoglycemia. To monitor real-time glucagon secretory response directly, we developed the technique of thin slices of the pancreas from D and N rats as well as normal human pancreas, subjected to perifusion with vehicle vs SSTR2a. SSTR2a treatment enhanced glucagon secretion in N and D rats and human pancreas. We conclude that SSTR2 antagonism can enhance hypoglycemia-stimulated glucagon release sufficient to achieve normoglycemic control.

Diss. (sammanfattning) Uppsala : Univ., 2003. / Härtill 4 uppsatser.

Thesis (M. Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 99-[110]).

Thesis (M.Phil.)--University of Hong Kong, 1999. / Includes bibliographical references (leaves 99-[110]) Also available in print.