Metabolic effects of autonomic blockade

Influence of beta-blocking drugs on glucose metabolism in patients with non-insulin dependent diabetes mellitus

Two beta-blocking agents, non-selective propranolol and beta1-selective metoprolol, were investigated with respect to their effects on glucose metabolism in 10 hypertensive patients with non-insulin dependent diabetes mellitus (NIDDM). The patients were treated randomly for two weeks in double-blind cross-over manner with (a) propranolol, (b) metoprolol, and (c) placebo. Propranolol impaired glucose tolerance when compared to placebo. The increase in blood glucose was associated neither with changes in concentrations of serum insulin, plasma glucagon of free fatty acid nor with alterations in peripheral insulin sensitivity as measured by 125I-insulin binding to mononuclear leukocytes. Although metoprolol had no effect on blood glucose, it increased 125I-insulin binding to mononuclear leukocytes. The increase in insulin binding could contribute to blood glucose control during metoprolol treatment. In search for reasons for poor metabolic control in NIDDM, treatment with non-selective beta-blockers should be kept in mind.

Influence of beta-blocking drugs on glucose metabolism in hypertensive, non-diabetic patients

Two beta-blocking agents, non-selective propranolol and beta 1-selective metoprolol, were investigated with respect to their effect on glucose metabolism in 11 hypertensive, non-diabetic patients. They were randomly treated for two weeks in a double-blind cross-over manner with propranolol, metoprolol and placebo. Both drugs caused a small but significant increase in basal blood glucose values as compared with placebo (p less than 0.01). Metoprolol increased the blood glucose concentrations during the first 10 min of an i.v. glucose tolerance test (IVGTT) as compared with placebo (p less than 0.02) and propranolol (p less than 0.05). Propranolol raised only the blood glucose values during the later part of the IVGTT (p less than 0.01). The increase in blood glucose concentrations was, however, not associated with significant changes in peripheral insulin levels. The mean basal glucagon concentrations were lower during propranolol and metoprolol than during placebo (p less than 0.01). Propranolol also induced a more pronounced reduction of plasma glucagon than placebo (p less than 0.05) at 10 min of the IVGTT. The mean basal free fatty acid (FFA) concentrations were lower during propranolol (p less than 0.001) and metoprolol (p less than 0.05) than during placebo. Both drugs decreased the plasma levels of FFA during the first 10 min of the IVGTT as compared with placebo (p less than 0.01 and p less than 0.02, respectively). Pharmacological doses of propranolol and metoprolol increased blood glucose concentrations, decreased plasma glucagon and FFA concentrations, but had no effect on serum insulin levels in hypertensive, non-diabetic subjects.

Effect of beta-blocking drugs on beta-cell function and insulin sensitivity in hypertensive non-diabetic patients

The effects of two beta-blocking drugs on endogenous insulin secretion and insulin sensitivity were investigated in a double-blind cross-over study in 13 hypertensive patients. The patients were randomly allocated to each of three 2-week treatment periods with propranolol 80 mg b.i.d., atenolol 50 mg b.i.d. and placebo b.i.d. Endogenous insulin secretion was assessed by measuring serum insulin and C-peptide before and 6 min after iv administration of glucagon; insulin sensitivity was determined by measuring insulin binding to erythrocytes, and as the glucose disappearance rate (KITT) after i.v. insulin. Fasting concentrations of serum free fatty acids (S-FFA) and plasma gastric inhibitory polypeptide (P-GIP) were also recorded during the three study periods. Both propranolol and atenolol reduced blood pressure, heart rate and S-FFA concentrations compared to placebo, and all patients showed measurable plasma concentrations of propranolol and atenolol. The results can be considered representative, therefore, of clinical beta-blockade. The two drugs did not significantly influence the fasting blood glucose level. There was an increase in fasting and glucagon-stimulated serum C-peptide concentration during propranolol therapy compared with placebo (p = 0.037 and p = 0.030, respectively), although this was not reflected by a significant change in serum insulin. Propranolol and atenolol did not significantly influence insulin binding to erythrocytes, but they clearly reduced the glucose disappearance rate KITT was compared to placebo (p = 0.0036 and p = 0.0003), respectively). The findings support the view that beta-blocking drugs can influence glucose metabolism by mechanisms other than inhibition of endogenous insulin secretion.

The influence of propranolol on catecholamine-induced changes in carbohydrate metabolism in the rabbit

In vitro evidence has indicated that isoproterenol (ISO) is more potent than epinephrine (EPI) in releasing glucose from rabbit liver slices and that propranolol (PROP) is a competitive antagonist of ISO. In contrast, dose-response data from fasted rabbits have shown that EPI is more potent than ISO in increasing plasma glucose levels and in lowering hepatic glycogen levels. Pretreatment with PROP abolished ISO-induced hyperglycemia and changes in liver and muscle glycogen levels whereas only the muscle glycogen depleting effect of EPI was altered significantly. These results suggest that factors other than stimulation of hepatic beta-receptors must be involved in EPI-stimulated depletion of liver glycogen and hyperglycemia in the intact rabbit.

Fat-mobilizing action of amphetamine

The effects of amphetamine and methamphetamine on plasma free fatty acid (FFA), blood glucose, serum total fat, and triglyceride concentrations were investigated in 21 subjects; the effect of epinephrine were studied in an identical manner in 14 subjects. The administration of amphetamine and methamphetamine led to an increase in the plasma FFA concentration. No significant changes were found in the blood glucose, serum total fat, and triglyceride concentrations. Kinetic studies of FFA were also made in some of the subjects receiving amphetamine, methamphetamine, and epinephrine. It was shown that amphetamine and methamphetamine lead to an augmentation of plasma FFA pool due to a primary increase of FFA production rate. Catecholamine depletion, by prolonged parenteral adminstration of reserpine, nearly completely abolished the adipokinetic action of amphetamine whereas the effect of epinephrine was greatly potentiated. This was interpreted as evidence for the dependence of the adipokinetic action of amphetamine on endogenous catecholamines. ESTIMATED FROM A DOSE RATIO (AMPHETAMINE: epinephrine) of 352:1, the relative adipokinetic potency of amphetamine, expressed as peak DeltaFFA rise, +DeltaFFA area, and DeltaFFA production rate, respectively, was found to be 55, 84, and 39% in comparison with the same effects of epinephrine. The more pronounced changes in +DeltaFFA area reflect the longer duration of action of amphetamine viz. epinephrine. This study demonstrates that amphetamine is an adipokinetic agent causing an increase in the plasma FFA pool of a lesser extent but of longer duration than equipressor doses of epinephrine. The mechanism of fat-mobilizing action of amphetamine is indirect i.e., dependent on endogenous catecholamine release.