Mechanism of glucoregulatory responses to stress and their deficiency in diabetes

Abstract

During exercise, increased energy demands are met by increased glucose production that occurs simultaneously with the increased glucose uptake. We had previously observed that, during exercise, metabolic clearance rate of glucose (MCR) increases markedly in normal, but only marginally in poorly controlled diabetic dogs. We wished to determine (i) whether in a more general model of stress matched increases in rate of appearance of glucose and MCR also occur, or if MCR is suppressed, as during catecholamine infusion; and (ii) whether diabetes affects stress-induced changes in rate of glucose appearance and MCR. Therefore, we injected carbachol (27 nmol/50 microliters), an analog of acetylcholine, intracerebroventricularly in seven conscious dogs before and after induction of alloxan diabetes. In normal dogs, plasma epinephrine and cortisol increased 4- to 5-fold, whereas norepinephrine and glucagon doubled. Plasma insulin, however, remained unchanged. Tracer-determined hepatic glucose production increased rapidly, but transiently, by 2.5-fold. This increment can be fully explained by the observed increments in the counterregulatory hormones. Surprisingly, however, MCR also promptly increased, and therefore, plasma glucose changed only marginally. After induction of diabetes, the animals were given intracerebroventricular carbachol while plasma glucose was maintained at moderate hyperglycemia (9.0 +/- 0.4 mM). Increments in counterregulatory hormones were similar to those seen in normal dogs, except for exaggerated norepinephrine release. Peripheral insulin levels were higher in diabetic than in normal dogs; however, MCR was markedly reduced and the lipolytic response to stress increased, indicating insulin resistance. Interestingly, the hyperglycemic response to stress was 6-fold greater in diabetic than normal animals, relating mainly to the failure of MCR to rise. Plasma lactate increased equivalently in diabetic and normal animals despite suppression of MCR in the diabetics, indicating either greater muscle glycogenolysis and/or impairment in glucose oxidation. We conclude that in this stress model MCR increases as in exercise in normal but not in diabetic dogs. We speculate that glucose uptake in stress could be mediated through an insulin-dependent neural mechanism.