Effects of propranolol on blood sugar, insulin and free fatty acids

Alpha- and beta- adrenergic receptors regulate inflammatory responses to acute and chronic sleep fragmentation in mice

Sleep is a recuperative process, and its dysregulation has cognitive, metabolic, and immunological effects that are largely deleterious to human health. Epidemiological and empirical studies have suggested that sleep fragmentation (SF) as result of obstructive sleep apnea (OSA) and other sleep abnormalities leads to pronounced inflammatory responses, which are influenced by the sympathetic nervous system (SNS). However, the underlying molecular mechanisms contributing to SNS regulation of SF-induced inflammation are not fully understood. To assess the effects of the SNS upon inflammatory responses to SF, C57BL/6j female mice were placed in automated SF chambers with horizontally moving bars across the bottom of each cage at specified intervals to disrupt sleep. Mice were first subjected to either control (no bar movement), acute sleep fragmentation (ASF), or chronic sleep fragmentation (CSF) on a 12:12-h light/dark schedule. ASF involved a bar sweep every 120 s for 24 h, whereas CSF involved a bar sweep every 120 s for 12 h (during 12 L; resting period) over a period of 4 weeks. After exposure to these conditions, mice received an intraperitoneal injection of either phentolamine (5 mg/kg BW; an α-adrenergic receptor blocker), propranolol (5 mg/kg BW; a β-adrenergic receptor blocker), or vehicle (saline). Serum corticosterone concentration, brain and peripheral cytokine (IL1β, TNFα, and TGFβ) mRNA expression, and body mass were assessed. ASF and CSF significantly elevated serum corticosterone concentrations as well as cytokine mRNA expression levels compared with controls, and mice subjected to CSF had decreased body mass relative to controls. Mice subjected to CSF and treated with phentolamine or propranolol had a greater propensity for a decrease in cytokine gene expression compared with ASF, but effects were tissue-specific. Taken together, these results suggest that both α- and β-adrenergic receptors contribute to the SNS mediation of inflammatory responses, and adrenergic antagonists may effectively mitigate tissue-specific SF-mediated inflammation.

Glucagon orchestrates stress-induced hyperglycaemia

Hyperglycaemia is commonly observed on admission and during hospitalization for medical illness, traumatic injury, burn and surgical intervention. This transient hyperglycaemia is referred to as stress-induced hyperglycaemia (SIH) and frequently occurs in individuals without a history of diabetes. SIH has many of the same underlying hormonal disturbances as diabetes mellitus, specifically absolute or relative insulin deficiency and glucagon excess. SIH has the added features of elevated blood levels of catecholamines and cortisol, which are not typically present in people with diabetes who are not acutely ill. The seriousness of SIH is highlighted by its greater morbidity and mortality rates compared with those of hospitalized patients with normal glucose levels, and this increased risk is particularly high in those without pre-existing diabetes. Insulin is the treatment standard for SIH, but new therapies that reduce glucose variability and hypoglycaemia are desired. In the present review, we focus on the key role of glucagon in SIH and discuss the potential use of glucagon receptor blockers and glucagon-like peptide-1 receptor agonists in SIH to achieve target glucose control.

Intermittent hypoxia-induced glucose intolerance is abolished by α-adrenergic blockade or adrenal medullectomy

Obstructive sleep apnea causes intermittent hypoxia (IH) during sleep and is associated with dysregulation of glucose metabolism. We developed a novel model of clinically realistic IH in mice to test the hypothesis that IH causes hyperglycemia, glucose intolerance, and insulin resistance via activation of the sympathetic nervous system. Mice were exposed to acute hypoxia of graded severity (21, 14, 10, and 7% O2) or to IH of graded frequency [oxygen desaturation index (ODI) of 0, 15, 30, or 60, SpO2 nadir 80%] for 30 min to measure levels of glucose fatty acids, glycerol, insulin, and lactate. Glucose tolerance tests and insulin tolerance tests were then performed under each hypoxia condition. Next, we examined these outcomes in mice that were administered phentolamine (α-adrenergic blockade) or propranolol (β-adrenergic blockade) or that underwent adrenal medullectomy before IH exposure. In all experiments, mice were maintained in a thermoneutral environment. Sustained and IH induced hyperglycemia, glucose intolerance, and insulin resistance in a dose-dependent fashion. Only severe hypoxia (7% O2) increased lactate, and only frequent IH (ODI 60) increased plasma fatty acids. Phentolamine or adrenal medullectomy both prevented IH-induced hyperglycemia and glucose intolerance. IH inhibited glucose-stimulated insulin secretion, and phentolamine prevented the inhibition. Propranolol had no effect on glucose metabolism but abolished IH-induced lipolysis. IH-induced insulin resistance was not affected by any intervention. Acutely hypoxia causes hyperglycemia, glucose intolerance, and insulin resistance in a dose-dependent manner. During IH, circulating catecholamines act upon α-adrenoreceptors to cause hyperglycemia and glucose intolerance.

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.

Glucose tolerance and insulin release in hypertensive patients treated with the cardioselective beta-receptor blocking agent metoprolol

Blood glucose and plasma insulin levels were studied under fasting conditions and following an i.v. and an oral glucose load, respectively, in nine males with moderate hypertension before treatment, after one month on placebo and after three months on the cardioselective beta-receptor blocking agent metoprolol. The studies were performed under metabolic ward conditions. The reproducibility of blood glucose and plasma insulin values following an i.v. glucose load was very good. Medication with metoprolol caused no changes in the fasting levels of blood glucose or plasma insulin, nor in the blood glucose response following a glucose load given i.v. or orally. The initial and total integrated insulin response to the i.v. administration of glucose was similar before and during metroprolol. Following oral glucose both the total integrated blood glucose response and the insulin response were unaffected by treatment with metoprolol.

Beta-adrenergic receptor blockers. Adverse effects and drug interactions

Adverse effects of beta-adrenergic receptor blocking drugs can be divided into two categories: 1) those that result from known pharmacological consequences of beta-adrenergic receptor blockade; and 2) other reactions that do not appear to result from beta-adrenergic receptor blockade. Adverse effects of the first type include bronchospasm, heart failure, prolonged hypoglycemia, bradycardia, heart block, intermittent claudication, and Raynaud's phenomenon. Neurological reactions include depression, fatigue, and nightmares. It is not yet proven whether the beta 1-selective adrenergic blockers or those with partial agonist activity reduce the overall frequency of adverse reactions seen with propranolol. Patient age does not appear, in itself, to be associated with more beta-blocker side effects. Side effects of the second category are rare. They include an unusual oculomucocutaneous reaction and the possibility of oncogenesis. There are also many drugs that interact with beta-blockers, which may increase toxicity. Finally, there are specific patient characteristics where one beta-blocker may be more effective and safer than another.

Beta-adrenergic blockers

beta-Adrenergic blocking drugs have been available for several years to treat ischemic heart disease and other cardiovascular and noncardiovascular disorders. There are multiple drugs in this class with various pharmacodynamic and pharmacokinetic properties that may be important in specific clinical situations and in avoiding certain adverse reactions. These drugs have been shown to be efficacious in relieving anginal symptoms and prolonging exercise tolerance, in reducing high blood pressure, for treating various arrhythmias, in therapy of hypertrophic cardiomyopathy, and for prolonging life in many survivors of acute myocardial infarction.

Cardiorespiratory response to exercise before and after acute beta-adrenoreceptor blockade in nonsmokers and chronic smokers

To evaluate the effects of chronic smoking on exercise performance we studied 5 smokers and 7 nonsmokers of comparable age and physical characteristics. The resting heart rate in smokers (75 +/- 3 beats/min; mean +/- SD) was significantly (P less than 0.01) higher than in nonsmokers (64 +/- 5). During exercise on a bicycle ergometer the heart rate remained significantly (P less than 0.01) higher in smokers than in nonsmokers. After exercise, the heart rate in nonsmokers settled to 78 +/- 9 beats/min at 10 minutes compared with 105 +/- 11 (P less than 0.01) in smokers. Oxygen consumption was similar in both groups throughout. Beta-adrenergic blockade reduced the exercise tachycardia in both groups but the heart rate for the same workload remained significantly (P less than 0.01) higher in smokers. Beta-blockade significantly reduced (P less than 0.05) oxygen consumption in nonsmokers but not in smokers who also incurred a significantly (P less than 0.05) greater oxygen debt and had higher serum lactate levels. These differences were attributed mainly to carboxyhaemoglobinaemia and partly to the effect of prolonged smoking on the heart and on intermediary metabolism.

Adrenergic blockade alters glucose kinetics during exercise in insulin-dependent diabetics

We investigated the effects of alpha and/or beta adrenergic blockade (with phentolamine and/or propranolol) on glucose homeostasis during exercise in six normal subjects and in seven Type I diabetic subjects. The diabetics received a low dose insulin infusion (0.07 mU/kg X min) designed to maintain plasma glucose at approximately 150 mg/dl. In normals, neither alpha, beta, nor combined alpha and beta adrenergic blockade altered glucose production, glucose uptake, or plasma glucose concentration during exercise. In diabetics, exercise alone produced a decline in glucose concentration from 144 to 116 mg/dl. This was due to a slightly diminished rise in hepatic glucose production in association with a normal increase in glucose uptake. When exercise was performed during beta adrenergic blockade, the decline in plasma glucose was accentuated. An exogenous glucose infusion (2.58 mg/kg X min) was required to prevent glucose levels from falling below 90 mg/dl. The effect of beta blockade was accounted for by a blunted rise in hepatic glucose production and an augmented rise in glucose utilization. These alterations were unrelated to changes in plasma insulin and glucagon levels, which were similar in the presence and absence of propranolol. In contrast, when the diabetics exercised during alpha adrenergic blockade, plasma glucose concentration rose from 150 to 164 mg/dl. This was due to a significant increase in hepatic glucose production and a small decline in exercise-induced glucose utilization. These alterations also could not be explained by differences in insulin and glucagon levels. We conclude that the glucose homeostatic response to exercise in insulin-dependent diabetics, in contrast to healthy controls, is critically dependent on the adrenergic nervous system.

The effect of adrenergic blockade on glucose-induced thermogenesis

The effect of alpha, beta, or combined sympathetic blockade on the increase in energy expenditure and concentrations of norepinephrine, glucose, and insulin following oral intake of 100 g of glucose was studied in lean subjects. Alpha blockade with intravenous (IV) phentolamine (n = 5) infusion increased oxygen consumption after glucose ingestion but no more than it increased the oxygen consumption when no glucose was given. Beta blockade with IV propranolol (n = 13) and combined alpha and beta blockade (n = 6) did not affect basal metabolic rate or the increase in metabolic rate after glucose ingestion. Phentolamine or combined propranolol plus phentolamine administration markedly increased plasma norepinephrine concentrations. Basal glucose and insulin concentrations were not affected by any of the infused drugs. Glucose-stimulated insulin concentrations were unchanged by propranolol and combined blockade, whereas there was a trend (P = 0.07) toward an increased response to glucose during phentolamine administration. These data do not support a role for the sympathetic nervous system in the increase in metabolic rate following glucose ingestion. The increase in metabolic rate during phentolamine administration can be attributed to beta adrenergic stimulation.

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.

Beta-adrenergic stimulation and blockade of the release of gastric inhibitory polypeptide and insulin in man

The effect of beta-adrenergic receptor stimulation with isoproterenol and blockade with propranolol on the release of gastric inhibitory polypeptide (GIP) and insulin was investigated in seven healthy volunteers. In the control experiment, the concentration of GIP in plasma increased from 30.1 (18.9-58.8) to 77.2 (44.2-121) pM after 30 g oral glucose. The concentration of insulin in serum increased from 7 (4-12) to 34 (13-76) mU/l. During infusion with isoproterenol, plasma GIP increased from 29.9 (25.7-39.1) to 47.1 (37.2-83.8) pM and insulin from 9 (5-15) to 37 (16-72) mU/l before oral glucose. After oral glucose, further increases of GIP to 111 (68.8-171) pM and of insulin to 103 (33-131) mU/l were observed. When propranolol was given in addition during this beta-receptor stimulation, plasma GIP after glucose increased to 82.2 (49.7-145) pM and serum insulin to 61 (9-133) mU/l. An isoproterenol-induced increase in the concentration of GIP and insulin was thus counteracted by propranolol. This strongly indicates that not only the insulin release but also the entero-insular axis as a total is influenced by beta-adrenergic mechanisms.

Sotalol in hyperthyroidism

Ten hyperthyroid patients were studied before and after 2 weeks' beta-adrenoceptor blockade with sotalol. The following variables were measured: resting pulse rate, blood pressure, weight, thyroid hormone levels, plasma lipids, alkaline phosphatase, plasma glucose and insulin responses to oral glucose, bromsulphthalein retention and the 24-h urinary excretion of calcium, hydroxyproline, creatine and creatinine. Sotalol produced a significant fall in pulse and blood pressure. Weight loss continued during treatment. No metabolic changes of any consequence were found. It is concluded that sotalol should not be used as the sole treatment of a patient with hyperthyroidism.

The effect of adrenoceptor blockade on the release of gastric inhibitory polypeptide after intraduodenal glucose in humans

An intravenous infusion of NaCl, NaCl + phentolamine (alpha-adrenoceptor antagonist), or NaCl + propranolol (beta-adrenoceptor antagonist) was given in three series of experiments. After intraduodenal infusion of glucose (82 ml 1.51 M, pH 6.5) the GIP concentration in plasma increased from 42.3 (23.1-62.2) to 225 (107-460) pM during intravenous NaCl, from 35.6 (17.3-38.9) to 251 (127-387) pM during phentolamine, and from 32.5 (5.5-63.4) to 172 (103-405) pM during propranolol administration. The blood glucose response was not different in the three experiments. It is concluded that the non-selective beta-adrenoceptor antagonist propranolol inhibits the release of GIP after intraduodenal administration of glucose.

Propranolol and blood glucose: simultaneous measurements over a wide range of doses and the effect of propranolol on the glucose tolerance test

No correlation was found between blood glucose and simultaneous measurements of plasma propranolol concentration in patients with schizophrenia, on a daily dose of 80 mg to 1800 mg of propranolol as an adjunct to phenothiazine medication. The Glucose Tolerance Test (GTT) in ten patients on propranolol and phenothiazines did not differ significantly from those of a matched control group on phenothiazine alone. Two patients with mild diabetes showed no significant change in their GTT after stopping propranolol. These observations accord with the view that relatively high doses of propranolol as an adjunct to phenothiazine medication in schizophrenia are safe from the standpoint of glucose metabolism. This does not apply to the insulin dependent diabetic who is in danger of severe hypoglycaemia when glycogenolysis is blocked by propranolol.

The effect of propranolol on hypoglycaemia. Observations in five insulinoma patients

Five hypoglycaemic hyperinsulinaemic patients (three with proven benign insulinoma, one with proven metastasizing insulinoma, one with probable insulinoma not found at surgery) were treated with propranolol for a variable time ranging from two weeks to one year. Three patients showed favourable clinical results and a significant increase of the mean basal blood glucose level was found while two patients showed no improvement of the frequency of neuroglycopenic episodes and no significant increase of their mean blood glucose level. No patient showed a significant decrease in mean basal IRI concentration. A decrease of insulinaemic responses was observed during oral and intravenous glucose tolerance tests, a prolonged fast, and tolbutamide and glucagon tests performed in some patients. The results suggest that propranolol may induce in certain patients an improvement of basal clinical status through not understood effects (probably hepatic), which leave the peripheral concentrations of insulin unchanged, whereas inhibition of insulin secretion may represent the main way by which the improvement of metabolic situation during physiological or pharmacological stimulation may have been achieved.

The metabolic consequences of adrenergic blockade: a reveiw

The effects in man of adrenergic blocking agents on plasma insulin, glucagon, growth hormone, and lipid metabolism are reviewed. Whereas basal insulin may be slightly inhibited by beta- and enhanced by alpha-adrenergic blockade, more marked suppression may be achieved under circumstances of high exogenous or endogenous catecholamine stimulation. The relative effects of beta1 or combined beta 1 and beta2 blockers in man are unknown. Glucagon release is probably provoked by beta- and inhibited by alpha-stimulation in man. Muscle glycogenolysis is inhibited by propranolol, and under situations of hepatic glycogen depletion, clinical hypopglycemia may occur. This may also account for the failure of significant hyperglycemia to be observed in short-term experiments on fasting subjects in whom insulin release may be suppressed and glucagon release enhanced. Growth-hormone release is enhanced by beta-adrenergic blockade. Free fatty acid formation in vivo is inhibited by intravenous beta blockade, but the effects of oral administration on triglyceride production and lipoprotein profiles remain uncertain. The inter-relationships between the effects of adrenergic blockade at different sites of hormone and substrate release are unclear but may have important consequences in alteration in carbohydrate tolerance and lipid metabolism. The relative effects of beta-blocking drugs with differing specificity must be determined.