Role of epinephrine-mediated beta-adrenergic mechanisms in hypoglycemic glucose counterregulation and posthypoglycemic hyperglycemia in insulin-dependent diabetes mellitus.

Initially euglycemic (overnight insulin-infused) patients with insulin-dependent diabetes mellitus (IDDM), compared with nondiabetic controls, exhibit similar, but somewhat delayed plasma glucose nadirs, delayed glucose recovery from hypoglycemia, and posthypoglycemic hyperglycemia after the rapid intravenous injection of 0.075 U/kg of regular insulin. These abnormalities are associated with and potentially attributable to markedly diminished glucagon secretory responses, partially reduced epinephrine secretory responses and delayed clearance of injected insulin in the diabetic patients. Because glucagon normally plays a primary role in hypoglycemic glucose counterregulation and enhanced epinephrine secretion largely compensates for glucagon deficiency, we hypothesized that patients with IDDM, who exhibit diminished glucagon secretory responses to hypoglycemia, would be more dependent upon epinephrine to promote glucose recovery from hypoglycemia than are nondiabetic persons. To test this hypothesis, glucose counterregulation during beta-adrenergic blockade with propranolol was compared with that during saline infusion in both nondiabetic controls and in patients with IDDM. Glucose counterregulation was unaffected by beta-adrenergic blockade in controls. In contrast, glucose recovery from hypoglycemia was significantly impaired during beta-adrenergic blockade in diabetic patients. This finding confirms the hypothesis that such patients are more dependent upon epinephrine-mediated beta-adrenergic mechanisms to promote glucose recovery from hypoglycemia and indicates that the measured deficiency of glucagon secretion is functionally important in patients with IDDM. Further, in the time frame of these studies, posthypoglycemic hyperglycemia was prevented by beta-adrenergic blockade in these patients. There was considerable heterogeneity among the diabetic patients with respect to the degree to which beta-adrenergic blockade limited the posthypoglycemic rise in plasma glucose. This rise was directly related to the degree of residual glucagon secretion and inversely related to plasma-free insulin concentrations.THUS, WE CONCLUDE: (a) that patients with IDDM are, to varying degrees, dependent upon epinephrine-mediated beta-adrenergic mechanisms to promote glucose recovery from hypoglycemia and that the degree of this dependence upon epinephrine is an inverse function of the residual capacity to secrete glucagon in response to hypoglycemia in individual patients; (b) that sympathoadrenal activation, coupled with the inability to secrete insulin, plays an important role in the pathogenesis of posthypoglycemic hyperglycemia in patients with IDDM.

Isolation from rat adipocytes of a chemical mediator for insulin activation of pyruvate dehydrogenase.

Insulin treatment of adipocytes increased the amount or activity of a low molecular weight, acid-stable material which, when isolated from intact adipocytes by heat extraction and subsequent Sephadex G25 chromatography, yielded a single active fraction that stimulated mitochondrial pyruvate dehydrogenase by activating the phosphatase and not by altering the kinase activity. Phosphatase activation was demonstrated by the ability of the active material to increase pyruvate dehydrogenase activity in the absence of ATP and by the ability of NaF, a phosphatase inhibitor, to this stimulation. Involvement of the kinase in this activation mechanism was eliminated by the fact that, in the presence of ATP, (1) NaF completely blocked the stimulation of pyruvate dehydrogenase by the active fraction, and (2) the stimulation of pyruvate dehydrogenase by dichloroacetic acid, a kinase inhibitor, was additive to the stimulation caused by the active fraction. This active fraction may contain an intracellular chemical mediator or second messenger for insulin.

Hypoglycemia due to serum-complexed insulin in a patient with diabetes mellitus.

A 28-year-old woman with insulin-dependent diabetes mellitus presented with a "hyperlabile" state of hyperglycemia and ketoacidosis alternating with hypoglycemia. Measurements of total and free insulin levels suggested that the clinical syndrome may have been due to antibody binding of insulin. Equilibrium analysis of insulin binding to the patient's serum demonstrated two classes of anti-insulin activities. The first class was of high affinity (dissociation constant approximately equal to 10(-9) M) and low capacity (150 microU/ml). At low total serum insulin concentrations, most of the circulating insulin was bound to the high-affinity binding activity, and the patient presented with hyperglycemia or ketosis. The second class of insulin binding activity had a lower affinity (dissociation constant approximately equal to 5 X 10(-7) M). The insulin that was bound to this low-affinity serum substance still maintained biologic activity in vivo. Isophane insulin (NPH) had a markedly prolonged serum half-life, which resulted in delayed hypoglycemia. Serum insulin complexes--that is, bound insulin--may not be "inactive" but may contribute to total insulin action. A determination of insulin activity, not only free insulin levels, may help explain hypoglycemia in selected patients with diabetes mellitus.

Oral propranolol and metoprolol both impair glucose recovery from insulin-induced hypoglycemia in insulin-dependent diabetes mellitus.

To the extent that they have deficient glucagon secretory responses to plasma glucose decrements, as they commonly do, patients with insulin-dependent diabetes mellitus (IDDM) are dependent on epinephrine-mediated beta-adrenergic mechanisms to promote recovery from hypoglycemia. Thus, they are at increased risk for prolonged hypoglycemia if treated with a nonselective beta-adrenergic antagonist such as propranolol. If the hyperglycemic actions of epinephrine are mediated through beta 2-adrenergic mechanisms, therapeutic efficacy (e.g., for hypertension or ischemic heart disease) could be accomplished without increased risk of hypoglycemia by selective beta 1-adrenergic blockade in such patients. However, oral administration of the relatively selective beta 1-adrenergic antagonist metoprolol (100 mg) and of the nonselective beta-adrenergic antagonist propranolol (80 mg) both impaired recovery from insulin-induced hypoglycemia in patients with IDDM. Thus, at a dose of 100 mg, oral metoprolol is not safer than oral propranolol with respect to recovery from hypoglycemia in patients with IDDM.

beta 2- and alpha 2-adrenergic receptors and receptor coupling to adenylate cyclase in human mononuclear leukocytes and platelets in relation to physiological variations of sex steroids.

In view of evidence, largely in animals, indicating effects of sex steroids on adrenergic receptors, we measured mononuclear leukocyte (MNL) beta 2-adrenergic receptors and adenylate cyclase sensitivity to stimulation by isoproterenol as well as platelet alpha 2-adrenergic receptors and sensitivity of sodium fluoride-stimulated adenylate cyclase to inhibition by epinephrine in 3 groups of normal humans with physiologically disparate levels of testosterone, estradiol, and progesterone (10 normal men and 10 normal women, the latter sampled in both the follicular and luteal phases of their menstrual cycles). Differences in testosterone, estradiol, and progesterone were as expected; testosterone levels were 10-fold higher in men, and progesterone levels were 20-fold higher in luteal phase women. T4, cortisol , and norepinephrine levels did not differ. Basal plasma epinephrine concentrations were slightly but significantly higher in luteal phase women [34 +/- 5 (+/-SE) pg/ml] than in follicular phase women (16 +/- 3 pg/ml; P less than 0.01) or men (20 +/- 3 pg/ml; P less than 0.05). There were no significant differences among these 3 groups in the densities or affinities of MNL beta 2-adrenergic or platelet alpha 2-adrenergic receptors or in the corresponding MNL and platelet adenylate cyclase sensitivities. Thus, there is not a generalized effect of physiological variations of testosterone, estradiol, and progesterone on adrenergic receptors or adenylate cyclase. To the extent that the adrenergic receptors and adenylate cyclase activities of circulating cells reflect those of extravascular catecholamine target cells, these data provide no support for a role of physiological variations of testosterone, estradiol, or progesterone in the regulation of catecholamine action in humans.