Amelioration of hypoglycemia via somatostatin receptor type 2 antagonism in recurrently hypoglycemic diabetic rats

Abstract

Selective antagonism of somatostatin receptor type 2 (SSTR2) normalizes glucagon and corticosterone responses to hypoglycemic clamp in diabetic rats. The purpose of this study was to determine whether SSTR2 antagonism (SSTR2a) ameliorates hypoglycemia in response to overinsulinization in diabetic rats previously exposed to recurrent hypoglycemia. Streptozotocin diabetic rats (n = 19), previously subjected to five hypoglycemia events over 3 days, received an insulin bolus (10 units/kg i.v.) plus insulin infusion (50 mU/kg/min i.v.) until hypoglycemia ensued (≤3.9 mmol/L) (experimental day 1 [Expt-D1]). The next day (Expt-D2), rats were allocated to receive either placebo treatment (n = 7) or SSTR2a infusion (3,000 nmol/kg/min i.v., n = 12) 60 min prior to the same insulin regimen. On Expt-D1, all rats developed hypoglycemia by ∼90 min, while on Expt-D2, hypoglycemia was attenuated with SSTR2a treatment (nadir = 3.7 ± 0.3 vs. 2.7 ± 0.3 mmol/L in SSTR2a and controls, P < 0.01). Glucagon response to hypoglycemia on Expt-D2 deteriorated by 20-fold in the placebo group (P < 0.001) but improved in the SSTR2a group (threefold increase in area under the curve [AUC], P < 0.001). Corticosterone response deteriorated in the placebo-treated rats on Expt-D2 but increased twofold in the SSTR2a group. Catecholamine responses were not affected by SSTR2a. Thus, SSTR2 antagonism after recurrent hypoglycemia improves the glucagon and corticosterone responses and largely ameliorates insulin-induced hypoglycemia in diabetic rats.

FIG. 1.

Blood glucose responses to repeated insulin-induced hypoglycemia. Antecedent hypoglycemia was induced by subcutaneous insulin injection (10 units/kg) and variable rate glucose infusion over a 3-day conditioning period in all rats (n = 19) (A). The next day (Expt-D1), rats were randomly allocated to either the control group (n = 7) (B) or the SSTR2a treatment group (n = 12) (C) for baseline assessment of counterregulatory responses by using a combination of insulin bolus (10 units/kg i.v.) and infusion (50 mU/kg/min i.v.) at the discretion of the investigator until moderate hypoglycemia ensued (target 3.0 mmol/L) (B). One day later, on Expt-D2, the insulin infusion treatment protocol was duplicated for each rat, either with (SSTR2a group) or without (controls) SSTR2a infusion (3,000 nmol/kg/min i.v.), which commenced 60 min prior to insulin treatment. Values are means ± SEM.

FIG. 2.

Percentage of rats that developed hypoglycemia, as measured by a blood glucose <4.0 mmol/L (A) or <3.5 mmol/L (B) in the control and SSTR2a-treated groups on Expt-D2.

FIG. 3.

Counterregulatory hormone responses to hypoglycemia in control and SSTR2a-treated rats on Expt-D1 and -D2. Plasma glucagon responses (A and B), plasma corticosterone responses (C and D), and plasma epinephrine responses (E and F) were determined for Expt-D1 (□) and Expt-D2 (■) in both groups. The integrated AUC for the hormonal responses to hypoglycemia is also shown (insets). Values are means ± SEM. *Expt-D2 was significantly different from Expt-D1 at P < 0.05.