Differences in metabolic responses to beta-adrenergic stimulation after propranolol or metoprolol administration

Metoprolol Versus Carvedilol in Patients With Heart Failure, Chronic Obstructive Pulmonary Disease, Diabetes Mellitus, and Renal Failure

This study compared the survival and the risk of heart failure (HF), chronic obstructive pulmonary disease (COPD), diabetes mellitus (DM), hypoglycemia, and renal failure (RF) hospitalizations in geriatric patients exposed to carvedilol or metoprolol. Data sources were Danish administrative registers. Patients aged ≥65 and having HF, COPD, and DM were followed for 1 year from the first β-blocker prescription redemption. Patients' characteristics were used to 1:1 propensity score match carvedilol and metoprolol users. A Cox regression model was used to compute the hazard ratio (HR) of study outcomes. For statistically significant associations, a conditional inference tree was used to assess predictors most associated with the outcome. In total, 1,424 patients were included. No statistically significant differences were observed for survival (HR 0.86; 95% confidence interval [CI] 0.67 to 1.11, p = 0.240) between carvedilol/metoprolol users. The same applied to COPD (HR 0.88; 95% CI 0.75 to 1.05, p = 0.177), DM (HR 0.95; 95% CI 0.82 to 1.10, p = 0.485), hypoglycemia (HR 0.88; 95% CI 0.47 to 1.67, p = 0.707), and RF (HR 1.25; 95% CI 0.93 to 1.69, p = 0.142) hospitalizations. Carvedilol users had a 38% higher hazard then metoprolol users of HF hospitalization during the follow-up period (HR 1.38; 95% CI 1.19 to 1.60, p <0.001). Artificial intelligence identified carvedilol exposure as the most important predictor for HF hospitalization. In conclusion, we found an increased risk of HF hospitalization for carvedilol users with this triad of diseases but no statistically significant differences in survival or risk of COPD, DM, hypoglycemia, and RF hospitalizations.

Role of the renal sympathetic nerve in renal glucose metabolism during the development of type 2 diabetes in rats

AIMS/HYPOTHESIS

Recent clinical studies have shown that renal sympathetic denervation (RDX) improves glucose metabolism in patients with resistant hypertension. We aimed to elucidate the potential contribution of the renal sympathetic nervous system to glucose metabolism during the development of type 2 diabetes.

METHODS

Uninephrectomised diabetic Otsuka Long-Evans Tokushima Fatty (OLETF) rats underwent RDX at 25 weeks of age and were followed up to 46 weeks of age.

RESULTS

RDX decreased plasma and renal tissue noradrenaline (norepinephrine) levels and BP. RDX also improved glucose metabolism and insulin sensitivity, which was associated with increased in vivo glucose uptake by peripheral tissues. Furthermore, RDX suppressed overexpression of sodium-glucose cotransporter 2 (Sglt2 [also known as Slc5a2]) in renal tissues, which was followed by an augmentation of glycosuria in type 2 diabetic OLETF rats. Similar improvements in glucose metabolism after RDX were observed in young OLETF rats at the prediabetic stage (21 weeks of age) without changing BP.

CONCLUSIONS/INTERPRETATION

Here, we propose the new concept of a connection between renal glucose metabolism and the renal sympathetic nervous system during the development of type 2 diabetes. Our data demonstrate that RDX exerts beneficial effects on glucose metabolism by an increase in tissue glucose uptake and glycosuria induced by Sglt2 suppression. These data have provided a new insight not only into the treatment of hypertensive type 2 diabetic patients, but also the pathophysiology of insulin resistance manifested by sympathetic hyperactivity.

Metabolic Effects of Pindolol and Propranolol in a Double-Blind Cross-Over Study in Hypertensive Patients

Metabolic effects of pindolol and propranolol were investigated in a randomised study of double-blind, double-dummy design in 39 Caucasians with newly detected hypertension. Each active treatment period was 6 months long. A euglycaemic hyperinsulinaemic clamp test was done to measure insulin sensitivity, and i.v. glucose tolerance was investigated with insulin determinations. Lipoprotein concentrations were quantified and lipoprotein lipase activities were determined in muscle and adipose tissue and in plasma after heparin injection. The blood pressure was significantly reduced by both regimes. The insulin sensitivity index was decreased by 34% during propranolol treatment and by 17% during pindolol treatment. The insulin concentrations in plasma were elevated at the end of the i.v. glucose tolerance test but were not high enough to compensate for the insulin resistance, so HbA1c and glucose concentrations were increased. A significant reduction of lipoprotein lipase activity in skeletal muscle during propranolol treatment probably explains the pronounced increase in serum triglyceride concentration during propranolol treatment despite lower free fatty acids and higher lipoprotein lipase activity in adipose tissue. These changes of lipoprotein lipase activity were not correlated to the changes in insulin sensitivity. In summary, the metabolic effects were significantly less pronounced with pindolol than with propranolol, which probably can be ascribed to the agonistic effect of pindolol on beta 2 adrenoceptors.

Adrenergic regulation of insulin release

Insulin release is influenced by the autonomic nervous system. In the periphery the regulation occurs via both alpha-adrenergic and beta-adrenergic receptors. The parasympathetic nervous system is important in the central regulation of insulin secretion. Nevertheless, adrenergic mechanisms are also concerned. This review discusses the mechanisms for the adrenergic regulation of insulin release and some clinical conditions where these mechanisms are concerned.

beta-Adrenoceptor blockade and exercise: effects on endurance and physical training

beta-adrenoceptor antagonists influence almost all haemodynamic and metabolic actions in the body. High levels of sympathetic stimulation accompany aerobic exercise and it is known that beta-blockade results in a decreased working capacity. Furthermore it has also been questioned whether beta-blockade inhibits the normal response to physical training. Although adrenergic mechanisms are involved in muscle and liver glycogen breakdown, beta-blockade does not seem to reduce glycogen utilisation during exercise. Both selective and non-selective beta-blockade inhibit lipolysis and result in less free fatty acids being available for muscle utilisation. Surgical and chemical sympathectomy in animals has been shown to inhibit the responses to physical training but results are now available showing that beta-adrenergic blockade does not prevent the effect of physical conditioning in patients treated with propranolol. It is concluded that beta-blockade during prolonged exercise a) does not reduce oxygen uptake by the working muscles b) decreases fat metabolism, which secondarily increases the use of carbohydrates, resulting in earlier hypoglycaemia and/or depletion of muscle glycogen with reduction in working capacity c) does not inhibit central and peripheral adaptation to physical conditioning.

Pharmacodynamic effects of prenalterol in healthy subjects

1. Prenalterol induces a dose-dependent effect on different variables reflecting myocardial contractility and heart rate. A clearcut effect can be demonstrated after an oral dose of 2.5 mg. The duration of the effect increases considerably when prenalterol is administered as a controlled release preparation partly due to an increased bioavailability. 2. Prenalterol induces a lipolytic effect manifested as a rise in free fatty acids and glycerol. Also a slight increase of plasma insulin is recorded while plasma potassium decreases somewhat. 3. When prenalterol is administered together with therapeutic doses of a selective or non-selective beta-adrenoceptor blocker it induces the same haemodynamic effects as before the beta-blocker but the dose has to be increased ten-fold. These results suggest that prenalterol might be a useful drug to counteract unwanted haemodynamic effects of a beta-blocker. 4. In animal studies it has been shown that prenalterol has affinity for both beta 1- and beta 2-adrenoceptors. However, it has a stimulating effect mainly on beta 1-adrenoceptors. Therefore, theoretically it might act as a beta 2-adrenoceptor antagonist. Preliminary results from studies in patients with chronic asthma indicate that prenalterol only has an insignificant beta 2-blocking effect when the drug is administered in doses which induce a significant beta 1-adrenoceptor stimulating effect.

The effect of beta-blockade on glucose tolerance and insulin release in adult diabetes

Blood glucose and plasma insulin levels were studied in ten adult diabetics treated in a cross-over fashion for at least three weeks with alprenolol, a non-selective beta-blocker, or with metoprolol, a cardioselective beta 1-blocker. Dietary intake was controlled three days prior to the study which comprised both i.v. and oral glucose tolerance tests. Mean fasting blood glucose levels were significantly higher on alprenolol than on metoprolol. The increase in fasting blood glucose was particularly pronounced in two patients. In these subjects the glucose tolerance following both an i.v. and an oral glucose load was reduced when treatment was switched from metoprolol to alprenolol. Lower plasma insulin levels in response to glucose were also found in these patients on alprenolol than on metoprolol. The mean insulin levels for all ten patients did not differ significantly between the two treatment periods. These data show that treatment with a non-selective beta-blocker can in some patients cause a considerable deterioration of the glucose tolerance, presumably due to inhibition of insulin release.

Adrenergic control of lipid metabolism

Adrenergic receptors are ubiquitous and mediate several important effects involving lipid metabolism. Thus, beta-adrenergic stimulation increases lipolysis and inhibits the activity of the lipoprotein lipase. In contrast, alpha-adrenergic stimulation inhibits fat cell lipid mobilisation. Unexpectedly, beta-adrenergic blockade increases plasma triglyceride levels and tends to lower the high density lipoprotein (HDL-cholesterol). These effects seem to be prevented or attenuated by concomitant alpha-blockade. Possible mechanisms for the adrenergic effect on lipid metabolism are reviewed.

Hypoglycemia Associated with Preoperative Metoprolol Administration

Perioperative beta(1)-selective-adrenergic antagonist administration has been shown to decrease morbidity and mortality in patients with cardiac disease undergoing surgical procedures. We report a case of a patient receiving the selective beta(1)-adrenergic antagonist, metoprolol, immediately before surgery that was associated with severe hypoglycemia. We postulate that an underlying abnormality in energy requirements or metabolism may allow for beta(1)-selective-adrenergic antagonists to precipitate hypoglycemia.

Betablocker treatment in diabetes mellitus

OBJECTIVES

Betablockers have been convincingly shown to reduce total and cardiovascular morbidity and mortality of hypertensive diabetic patients. In diabetic patients, after myocardial infarction, these agents confer a twice as high protective effect when compared to non-diabetic patients. However, most paradoxically, betablocking agents are used less frequently in diabetes. Control of hypertension is insufficient in most of the diabetic patients, probably because a combination of antihypertensive agents including betablockers is frequently needed to sufficiently control blood pressure but is not used in these patients. The fear of betablocker-associated side effects in diabetes may be partly responsible for the frequent antihypertensive mono-therapy and the resulting poor quality of blood pressure control among diabetic patients.

DESIGN

We have performed an analysis of the literature to assess whether possible adverse metabolic effects, a higher risk of hypoglycaemia or less nephroprotective effects of beta1-selective betablocking agents could justify the reticence in prescribing these antihypertensive agents to diabetic patients.

RESULTS

A thorough review of the literature does not indicate that beta1-selective betablocking agents have important adverse effects on glucose metabolism, prolong hypoglycaemia or mask hypoglycaemic symptoms. In diabetic nephropathy, betablockers are as nephroprotective as angiotensin converting enzyme inhibitors.

CONCLUSIONS

The unnecessary less frequent prescription of beta1-selective betablockers in diabetes mellitus may contribute to the higher cardiovascular mortality among these patients.

Requirements for antihypertensive therapy in diabetic patients: metabolic aspects

AIM OF ANTIHYPERTENSIVE TREATMENT IN DIABETICS: Prevention or treatment of hypertensive in diabetic patients reduces the incidence and progression of diabetic complications of retinopathy and nephropathy, cerebro- and cardio-vascular disease, and widespread macroangiopathy. Therefore, in patients with diabetes and hypertension beside good glucose control, the basic and probably major intervention steps is to normalize blood pressure. Antihypertensive treatment usually means life-long use of antihypertensive drugs. METABOLIC EFFECTS OF DIFFERENT DRUG CLASSES: Given the known diabetogenic properties of several antihypertensive drugs and their high rate of use, in probably a substantial proportion of patients with diabetes or prone to develop diabetes, treating arterial hypertension with conventional diuretics and/or beta-blockers might, in the long term, offset the beneficial effects of lowering blood pressure. Furthermore, there are conflicting reports of increased mortality in patients treated with diuretics, beta-blockers or calcium antagonists. Consequently, metabolic aspects and side effects of antihypertensive drugs are key elements in determining the preference for a specific antihypertensive regimen. Although the impact of hyperinsulinemia/insulin resistance on morbidity and mortality is an open question, it is preferable that antihypertensive treatment does not increase insulin resistance and/or hyperinsulinemia. Chronic beta-blocker treatment can be accompanied by an increase in insulin resistance. Calcium antagonists and angiotensin converting enzyme (ACE) inhibitors and alpha(1)-blockers are neutral or might even improve insulin resistance and lipid profile. Thiazides impair glucose tolerance, increase low-density lipoprotein cholesterol and decrease potassium, although these side effects are dose-dependent. Unless diuretics are needed for reasons other than hypertension, treatment of diabetics with thiazides should be avoided until the influence of these agents on prognosis is clarified. If the addition of a diuretic is needed, the metabolically neutral indapamide would seem a reasonable choice. PREFERRED FIRST-LINE TREATMENT: On the basis of favorable pharmacological profiles, ACE inhibitors and certain calcium antagonists have emerged as the preferred first-line drugs in the treatment of the hypertensive diabetic patient. In diabetics with nephropathy, therapy is usually initiated with an ACE inhibitor. Moreover, the combination of an ACE inhibitor and a calcium antagonist that lowers the heart rate (such as verapamil) might offer even greater advantages than either class of drug alone, since they combine metabolic neutrality with added antihypertensive and renal protective efficacy.

Four week administration of an ACE inhibitor and a cardioselective beta-blocker in healthy volunteers: no influence on insulin sensitivity

In most, but not all, studies antihypertensive treatment with angiotensin converting enzyme inhibitors (ACE inhibitors) improves insulin sensitivity, whereas beta-blockers decrease insulin sensitivity. However, there was a significant increase in body weight with beta-blockers and changes in the body potassium homeostasis with ACE inhibitors. In order to compare the drug specific metabolic effects of an ACE inhibitor and a cardioselective beta-blocker controlling these factors, we measured insulin sensitivity in a randomized, double-blind cross-over study in 22 healthy volunteers (age 27 +/- 3 years; BMI 22.0 +/- 1.5 kg m-2 (mean +/- SD)) during euglycaemic glucose clamps before and after 4 weeks' administration of 5 mg Lisinopril or 5 mg Bisoprolol. Both drug phases were separated by 4 weeks of no drug administration. During the insulin sensitivity measurements potassium concentrations were clamped at basal levels by means of a variable i.v. potassium infusion. Body weight was monitored at weekly intervals and kept constant within +/- 1 kg of the subjects' baseline weight throughout the entire study period. Insulin sensitivity did not change significantly during either drug administration period. The insulin sensitivity index of the 22 volunteers after administration of the ACE inhibitor was 7.9 +/- 2.4 mL min-1 m2 microU-1 mL-1 (basal index 8.3 +/- 1.9 mL min-1 m2 microU-1 mL-1, and 7.5 +/- 2.1 mL min-1 m2 microU-1 mL-1 after administration of the beta-blocker (basal index 8.2 +/- 1.9 mL min-1 m2 microU-1 mL-1; NS).(ABSTRACT TRUNCATED AT 250 WORDS)

Randomized trial of insulin-glucose infusion followed by subcutaneous insulin treatment in diabetic patients with acute myocardial infarction (DIGAMI study): effects on mortality at 1 year

OBJECTIVES

We tested how insulin-glucose infusion followed by multidose insulin treatment in diabetic patients with acute myocardial infarction affected mortality during the subsequent 12 months of follow-up.

BACKGROUND

Despite significant improvements in acute coronary care, diabetic patients with acute myocardial infarction still have a high mortality rate.

METHODS

A total of 620 patients were studied: 306 randomized to treatment with insulin-glucose infusion followed by multidose subcutaneous insulin for > or = 3 months and 314 to conventional therapy.

RESULTS

The two groups were well matched for baseline characteristics. Blood glucose decreased from 15.4 +/- 4.1 to 9.6 +/- 3.3 mmol/liter (mean +/- SD) in the infusion group during the 1st 24 h, and from 15.7 +/- 4.2 to 11.7 +/- 4.1 among control patients (p < 0.0001). After 1 year 57 subjects (18.6%) in the infusion group and 82 (26.1%) in the control group had died (relative mortality reduction 29%, p = 0.027). The mortality reduction was particularly evident in patients who had a low cardiovascular risk profile and no previous insulin treatment (3-month mortality rate 6.5% in the infusion group vs. 13.5% in the control group [relative reduction 52%, p = 0.046]; 1-year mortality rate 8.6% in the infusion group vs. 18.0% in the control group [relative reduction 52%, p = 0.020]).

CONCLUSIONS

Insulin-glucose infusion followed by a multidose insulin regimen improved long-term prognosis in diabetic patients with acute myocardial infarction.

Beta-adrenoceptor subtypes mediating the airways response to BRL 35135 in man

1 The purpose of the study was to assess the bronchorelaxant effects of the beta3-adrenoceptor agonist BRL 35135 in normal human airways. 2 Eight healthy male subjects were studied, having previously demonstrated airways responsiveness to inhaled salbutamol 200 microg, with a group mean (+/- s.e. mean) fall in airways resistance (Raw), from baseline, of 37 +/- 5%. 3 Subjects attended the laboratory on 3 separate days, having fasted and taken placebo (PL) or nadolol 20 mg (N20), 2 h previously. 4 After 30 min rest, baseline measurements of Raw, serum potassium, glucose and free fatty acid were performed before subjects were given single oral doses of BRL 35135 8 mg (BRL) or placebo BRL. Measurements were repeated 60 min after the BRL or placebo BRL were given. 5 There was a significant (P < 0.05) fall in Raw (% change from baseline, as means and 95% CI) with PL/BRL: -32(-18, -46), compared with either PL/PL: -8(5, -21), or N20/BRL: -11(2, -24). There was no significant difference between PL/PL and N20/BRL. 6 A similar pattern to Raw was observed for both of the beta2-mediated metabolic responses which were also antagonised by nadolol. For the potassium response (mmol l(-1)), there was a significant (P < 0.05) difference between PL/BRL: -0.50(-0.31, -0.69), in comparison with either PL/PL: 0.08(-0.11, 0.27) or N20/BRL: 0.09(-0.10, 0.28), but values for PL/PL and N20/BRL were not significantly different. In contrast, with the free fatty acid response (nmol 1(-1)), the increase seen with N20/BRL: 85(1.0, 171.0) was significantly (P < 0.05) different from PL/PL: 3.7(-82.3, 89.8), but was not different from PL/BRL: 132.5(46.5, 218.5). 7 In conclusion, BRL 35135 produced airways, potassium and glucose responses which were antagonised by nadolol, whereas the lipolysis response was not. This suggests that there are not functional beta3-adrenoceptors in human airways.

Metabolic effects of beta 2-agonists

Catecholamines produce a number of biochemical changes most of which result from stimulation of beta 2-receptors. Interest in these metabolic effects has increased recently as a consequence of the concern over the relatively high mortality from acute asthma attacks. In this review the data on the impact of beta 2-agonists on glucose production, insulin release and lipolysis are presented. Thereafter the subject of hypokalaemia, the mechanism for its production by beta 2-agonists and its relevance to cardiac arrhythmias are considered in detail. Finally the fall in plasma magnesium and the possible role of beta 2-agonists in the production of lactic acidosis are discussed.

Antihypertensive agents, serum lipoproteins and glucose metabolism

Effective blood pressure control with traditional high-dose diuretic therapy has led to a distinct decrease in cerebrovascular morbidity and mortality, but failed to achieve a satisfactory reduction of coronary complications and sudden death. The same applies also for beta blockers, although they have been shown to be effective in secondary prevention of myocardial infarction. It is suspected that conventional antihypertensive treatment has an unfavorable effect on coronary risk factors other than hypertension. For instance, thiazide-type diuretics can impair glucose tolerance and increase the potentially atherogenic serum low-density lipoprotein (LDL) cholesterol fraction and triglycerides. Beta blockers without partial intrinsic sympathomimetic activity increase serum triglycerides and tend to lower the potentially antiatherogenic high-density lipoprotein (HDL) cholesterol. Certain beta blockers may also impair glucose tolerance, particularly when they are combined with diuretics. Calcium channel blockers, angiotensin converting-enzyme inhibitors and alpha 1-receptor blockers do not adversely affect lipoprotein or carbohydrate profiles. The latter two drug classes may even increase insulin sensitivity, and alpha 1 blockers may also slightly improve lipid metabolism. The prognostic relevance of drug-induced dyslipidemia and/or glucose intolerance awaits further clarification. In the meantime, it is of clinical interest that several of the generally available antihypertensive drugs seem to be metabolically neutral or sometimes perhaps even potentially beneficial with regard to the lipoprotein and carbohydrate metabolism.

Glucose-induced or postprandial hyperinsulinemia in mild essential hypertension--an underestimated biochemical risk indicator?

Even if glucose tolerance is normal, a glucose-stimulated or postprandial hyperinsulinemia can frequently be observed in patients with early stages and mild forms of essential hypertension. Numerous epidemiological, clinical and experimental data suggest that hyperinsulinemia might be an independent risk factor for atherosclerosis which should be paid more attention. It could be hypothesized that, apart from the haemodynamic phenomenon of high blood pressure, the postprandial hyperinsulinemia of patients with mild essential hypertension might be relevant to their cardiovascular risk.

Investigation of the effects of beta-2 stimulation on free fatty acids in man

In this study we present evidence that lipolysis in man is under beta-2 adrenergic control and that beta-2 stimulation produces a characteristic profile of individual free fatty acid (FFA) release. Twelve healthy volunteers received infusions of placebo (N Saline), terbutaline (a selective beta-2 agonist) and dilevalol (a new non-selective beta-blocker with beta-2 agonist activity). Plasma FFA concentrations during and after the infusions were measured using gas chromatography. A significant rise in total and individual FFAs was seen after 30 min of terbutaline infusion. This was most marked for oleic acid. Total and individual FFA concentrations also rose after 30 min of dilevalol infusion; this was only significant for oleic acid and was approximately 15% of the rise induced by terbutaline infusion. Placebo infusion did not cause any significant changes in FFA levels.

Metabolic, electrocardiographic, and hemodynamic responses to increased circulating adrenaline: effects of selective and nonselective beta adrenoceptor blockade

Twelve healthy male volunteers were given adrenaline infusions, 0.05 microgram/kg body weight/minute over one hundred twenty minutes (min), in order to achieve serum adrenaline concentrations comparable with those seen in acute myocardial infarction. The infusions were given on three occasions, at intervals of at least four weeks. Before the infusions the subjects were given, in random order, two days' pretreatment with placebo, a beta-1-selective adrenoceptor blocker (atenolol), or a nonselective beta blocker (propranolol) with each subject receiving each pretreatment. Six of the volunteers also had a fourth adrenaline infusion, after two days' pretreatment with a beta-2-selective beta blocker, ICI 118551. Adrenaline increased heart rate by 11 beats/min, increased systolic blood pressure by 10 mmHg, and decreased diastolic blood pressure by 15 mmHg. These changes were partly prevented by atenolol. Propranolol and ICI 118551 partly prevented the rise in systolic blood pressure but differed from atenolol in their effects on heart rate and diastolic blood pressure, causing falls in heart rate by 7 beats/min and 12 beats/min respectively, secondary perhaps to increases in diastolic blood pressure by 13 mmHg and 17 mmHg respectively. Adrenaline caused a prolongation of QTc duration by 0.03 second and a flattening of the T-wave amplitude by 1.04 mm. These changes in cardiac repolarization were partly inhibited by atenolol, but the effects of propranolol and ICI 118551 were greater, each causing a reduction of QTc and an increase in T-wave amplitude. During adrenaline infusion S-potassium declined by 0.60 mmol/L, S-magnesium by 0.05, S-calcium by 0.10, and S-phosphate by 0.24, but S-free fatty acids increased nearly threefold. All these changes were statistically significant and were presumably mediated mainly by the beta-2-adrenoceptor, for they were blocked more effectively by the beta-2-adrenoceptor blockers than by the selective beta-1-adrenoceptor blocker. B-glucose increased by 4.1 mmol/L, the increase being practically unaffected by the different pretreatments. These adrenaline-induced hemodynamic, electrocardiographic, and metabolic changes may predispose to arrhythmias and impair cardiac performance after a myocardial infarction. Nonselective beta blockers may be more effective in blocking the electrocardiographic and metabolic effects, but beta-1-selective beta blockers may have hemodynamic advantages.

A comparison of the effects of flosequinan, a new vasodilator, and propranolol on sub-maximal exercise in healthy volunteers

1. The effects of steady state flosequinan, a new vasodilator, and propranolol, on glucose mobilisation, lipolysis and plasma potassium concentration during sub-maximal exercise testing were investigated in a double-blind, randomised, three-way crossover study in 12 healthy volunteers. 2. Plasma glucose, potassium and free fatty acid concentration during and after exercise on flosequinan were similar to those on placebo. Exercise heart rates were 7% (+9.2 beats min-1) higher on flosequinan compared with placebo (P less than 0.05). During exercise on propranolol plasma glucose concentrations were comparable with those on placebo but plasma potassium concentrations were higher (mean increase 0.26 mmol l-1, P less than 0.01) whereas free fatty acid concentrations were lower (mean decrease 0.10 mmol 1-1, P less than 0.01). As expected the heart rate on exercise was 25% less (-35 beats min-1) on propranolol (P less than 0.05). 3. These data suggest that, in contrast to propranolol, flosequinan does not adversely affect the mobilisation of the two major sources of energy during sub-maximal exercise.

Sensitivity to insulin during treatment with atenolol and metoprolol: a randomised, double blind study of effects on carbohydrate and lipoprotein metabolism in hypertensive patients

OBJECTIVE

To compare the effects of metoprolol and atenolol on carbohydrate and lipid metabolism and on insulin response to an intravenous glucose load.

DESIGN

Randomised, double blind, double dummy, controlled crossover trial.

SETTING

University Hospital, Uppsala, Sweden.

PATIENTS

60 Patients with primary hypertension (diastolic blood pressure when resting supine 95-119 mm Hg on at least two occasions during four to six weeks of treatment with placebo) randomised to receive either metoprolol (n = 30) or atenolol (n = 30) during the first treatment period.

INTERVENTIONS

Placebo was given for a run in period of four to six weeks. Metoprolol 100 mg twice daily or atenolol 25 mg twice daily was then given for 16 weeks. The two drugs were then exchanged and treatment continued for a further 16 weeks.

END POINT

Evaluation of effects of treatment with metoprolol and atenolol on glucose, insulin, and lipid metabolism and glucose disposal mediated by insulin.

MEASUREMENTS AND MAIN RESULTS

Reduction of blood pressure was similar and satisfactory during treatment with both drugs. Glucose uptake mediated by insulin was measured during a euglycaemic hyperinsulinaemic clamp to evaluate patients' sensitivity to insulin. Glucose uptake decreased from 5.6 to 4.5 mg/kg/min when patients were taking metoprolol and from 5.6 to 4.9 mg/kg/min when they were taking atenolol. Both drugs caused a small increase in fasting plasma insulin and blood glucose concentrations and glycated haemoglobin concentration. Despite decreased sensitivity to insulin the increase in insulin concentration in response to an intravenous glucose tolerance test was small, suggesting inhibition of release of insulin. Very low density lipoprotein and low density lipoprotein triglyceride concentrations were increased with both drugs and high density lipoprotein cholesterol concentration was decreased. Low density lipoprotein cholesterol concentration was not affected.

CONCLUSIONS

Long term use of metoprolol and atenolol causes metabolic abnormalities that may be related to the increased incidence of diabetes in patients with hypertension who are treated pharmacologically. These results may help to explain why the two drugs have failed consistently to reduce the incidence of coronary heart disease in several large scale studies.

Evaluation of the metabolic responses to inhaled salbutamol in the measurement of beta 2-adrenoceptor blockade

The aim of the present study was to evaluate whether metabolic responses to inhaled salbutamol may be used to measure the cardioselectivity of beta-adrenoceptor antagonists. We therefore studied the effects of oral doses of atenolol 50 mg, 100 mg, 200 mg (A50, A100, A200), propranolol 40 mg (P40), and placebo (Pl) on the hypokalaemic (K) and hyperglycaemic (Glu) responses to inhaled salbutamol in five healthy subjects. Increasing doses of atenolol were associated with a progressive attenuation of delta K compared with placebo: -0.72 mmol.l-1 (Pl) vs -0.20 mmol.l-1 (A200). However, delta K with A200 was significantly different from the response with P40: +0.12 mmol.l-1. There were partial reductions in the hyperglycaemic response with the beta-adrenoceptor antagonists, although this was only significant (compared with Pl) for P40: delta Glu 1.92 mmol.l-1 (Pl) vs 0.76 mmol.l-1 (P40). These results show that beta 2-adrenoceptor blockade by atenolol is a dose-dependent phenomenon, which may be measured by the attenuation of salbutamol-induced hypokalaemia. However, beta 2-adrenoceptor blockade by atenolol 200 mg was less than that by propranolol 40 mg. The glucose response to salbutamol was only partially blocked by propranolol and may therefore not be suitable to assess beta 2-adrenoceptor antagonism.

The assessment of the beta-adrenoceptor blocking activity and cardioselectivity of Koe 3290 in normal subjects

1. The beta-adrenoceptor antagonist activity, cardioselectivity and antilipolytic properties of Koe 3290 were investigated in healthy subjects. 2. Koe 3290 12.5, 25, 50 and 100 mg, atenolol 25, 50 and 100 mg and placebo were given in double-blind randomised order to eight subjects. All doses of both Koe 3290 and atenolol reduced supine, standing and exercise heart rate (P less than 0.02). From 2 to 8 h after administration the exercise heart rate after Koe 3290 100 mg was similar to that for atenolol 50 mg. 3. The cardioselectivity of Koe 3290 and atenolol was compared. Koe 3290 50, 100 and 150 mg, atenolol 50 and 100 mg and placebo were given to six subjects in a double-blind random order. Isoprenaline dose-response curves were constructed for cardiovascular parameters and finger tremor. 4. For doses which were equipotent at the beta 1-adrenoceptor (Koe 3290 100 mg and atenolol 50 mg) atenolol caused less attenuation of heart rate, diastolic blood pressure, forearm blood flow and finger tremor (P less than 0.02). 5. There was no difference in the isoprenaline-induced changes in serum free fatty acids, blood glucose, plasma lactate or potassium after Koe 3290 and atenolol. Koe 3290 attenuated the rise in serum insulin more than atenolol (P less than 0.02). 6. Koe 3290 is an effective beta-adrenoceptor blocking drug in man. It is not as cardioselective as atenolol and does not possess specific antilipolytic properties.

The assessment in man of the beta-adrenoceptor blocking activity and cardioselectivity of H-I 42 BS, a long acting beta-adrenoceptor blocking drug

The pharmacokinetic and pharmacodynamic effects of the beta-adrenoceptor antagonist H-I 42 BS were examined in healthy subjects. In an open dose ranging study, H-I 42 BS 50, 100, 200 and 400 mg were given as single oral doses to four subjects. H-I 42 BS 400 mg caused maximum reduction in exercise heart rate (20.4 +/- 1.0%--mean +/- s.d.) at 4 h and still reduced exercise heart rate at 96 h (18.4 +/- 7.2%). Seven subjects received in double-blind, randomised order, single oral doses of H-I 42 BS 50, 100 and 200 mg, atenolol 50 and 100 mg and placebo. H-I 42 BS 400 mg was given in a single blind manner as the last dose of the study. Both H-I 42 BS and atenolol reduced supine and standing heart rate and systolic blood pressure (P less than 0.05) although atenolol had the more marked effect. The maximum percent reduction of exercise heart rate after H-I 42 BS 50 mg was 10.9 +/- 7.1%, after 100 mg was 18.7 +/- 5.8%, after 200 mg was 20.6 +/- 6.4% and after 400 mg was 21.9 +/- 8.2%. H-I 42 BS 400 mg still caused 11.0 +/- 3.5% reduction at 168 h. Atenolol 50 mg caused maximum percent reduction of exercise heart rate of 26.0 +/- 6.0% but did not reduce exercise heart rate after 24 h. The mean peak plasma concentrations for all doses of H-I 42 BS occurred at 5.1 +/- 1.5 h. The plasma elimination half-life was 47.6 +/- 8.1 h. There was a linear correlation between the dose and AUC0-infinity (r = 0.97). The cardioselectivity of H-I 42 BS and atenolol was compared. Six subjects received in double-blind random order H-I 42 BS 100 and 400 mg, atenolol 50 mg and placebo. After each dose, graded infusions of isoprenaline were given until the heart rate increased by 50 beats min-1. Dose-response curves for heart rate, diastolic blood pressure, forearm blood flow and finger tremor were constructed. There was no difference in the dose-response curves for forearm blood flow or finger tremor after H-I 42 BS 400 mg or atenolol 50 mg. Atenolol 50 mg caused more attenuation (P less than 0.01) of the diastolic blood pressure response. These results indicate that H-I 42 BS is a cardioselective beta-adrenoceptor antagonist with a long duration of action in man.

Differences between acute and long-term metabolic and endocrine effects of oral beta-adrenoceptor agonist therapy with pirbuterol for cardiac failure

The metabolic, hormonal and haemodynamic effects of oral pirbuterol, a new beta 2-adrenoceptor agonist, were studied acutely (n = 19) and after 3 months treatment (n = 11) in patients with severe heart failure receiving chronic frusemide therapy. In the acute study fasted patients (n = 10) showed reductions in plasma K+ (P less than 0.005) and cortisol (P less than 0.01) and increases in plasma glucose (P less than 0.005), insulin (P less than 0.01), lactate (P less than 0.005) and pyruvate (P less than 0.0025). These acute changes were less in unfasted subjects (n = 9). Maximal increase in stroke volume occurred at approximately half the plasma pirbuterol concentration required for maximal effect on plasma insulin. Treatment with pirbuterol for 3 months was associated with sustained increases in stroke volume and fasting plasma glucose and insulin, but there was loss of all other acute metabolic effects. Despite concurrent frusemide and digoxin therapy acute hypokalaemia caused no adverse effects. Hypokalaemia did not occur with chronic pirbuterol administration.

The mechanism of salbutamol-induced hypokalaemia

The following four intravenous treatments were administered in a balanced, randomized Latin square design to eight healthy volunteers: (-)-adrenaline (0.06 microgram kg-1 min-1 for 90 min) + vehicle control (+)-glucose infusion (60 min), salbutamol (120 ng kg-1 min-1 for 30 min) + vehicle control (+)-glucose infusion (90 min), (-)-adrenaline (0.06 microgram kg-1 min-1 for 90 min) + salbutamol (120 ng kg-1 min-1 for 30 min) and two vehicle control infusions of (+)-glucose. All active solutions were preceded by a 1 h control infusion and the control infusion was continued for 1 h following the active solutions. Both the active solutions, (-)-adrenaline and salbutamol were increased stepwise to the above doses. Heart rate and blood pressure were recorded at frequent intervals throughout and venous blood was taken for the estimation of potassium, insulin, glucose, catecholamine and salbutamol levels. Adrenaline levels similar to those seen in acute illness were achieved using this infusion protocol. Salbutamol levels rose throughout the period of the salbutamol infusions and steady-state was not achieved. Potassium levels were unchanged on the control + control study day and fell on all active treatments (0.45 mmol l-1 following (-)-adrenaline + control; 0.48 mmol l-1 following salbutamol + control; 0.93 mmol l-1 following (-)-adrenaline + salbutamol). Insulin levels rose insignificantly after salbutamol alone and fell slightly on all other treatments.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism of exercising skeletal muscle during beta 1-selective adrenoceptor blockade

Concentrations of glycogen, glucose, glucose-6-phosphate and lactate in the lateral vastus muscle were measured in seven subjects before and after dynamic muscle exercise at a work load of 75% of each subject's maximal working capacity, and with and without intravenous administration of the beta 1-selective beta-adrenoceptor blocking agent, atenolol. Pulmonary oxygen uptake was measured during exercise. Heart rate and arterial blood pressure were measured throughout the study. Arterial concentrations of glucose, lactate and free fatty acids were measured at rest and during exercise. The muscle concentration of glycogen and the extent of glycogen depletion with exercise were not influenced by the beta 1-adrenoceptor blocker. Similarly, there was no change in the muscle concentrations of glucose, glucose-6-phosphate and lactate. Heart rate decreased at rest and during exercise. Arterial blood pressure was not influenced by beta-blockade. Pulmonary oxygen uptake decreased by 6.5%. The exercise induced rise in arterial blood concentration of free fatty acids was abolished by beta 1-selective beta-blockade. It is concluded that the decrease in lactate release from exercising muscles during beta 1-adrenoceptor blockade seen in other studies cannot be explained by an impaired breakdown of muscle glycogen. It may be inferred, however, that a reduced availability of free fatty acids in the exercising muscles during beta 1-selective (and non-selective) beta-blockade may enhance the combustion of pyruvic acid and thereby decrease the production of lactate.

Effects of beta non-selective and beta 1 selective adrenergic blocking agents on glucagon secretion from isolated perfused rat pancreas

To characterize beta-receptors which affect pancreatic A-cell activity, the effects of propranolol (beta non-selective blockade) and metoprolol (beta 1 selective blockade) were evaluated on epinephrine modulated insulin (IRI) and glucagon (IRG) release both in basal state and during metabolic stimulus (arginine 20 mM). The isolated perfused rat pancreas model with the exclusion of stomach and duodenum was used. Epinephrine infusion (at 10(-7) M) caused a prompt and sustained increase in basal IRG secretion and significantly potentiated glucagon release in response to metabolic stimulus. Insulin secretion was markedly suppressed by epinephrine both in basal conditions and during metabolic stimulus. Propranolol (at 10(-7) M) and metoprolol (at 10(-7) M) infusion clearly and similarly counteracted epinephrine stimulatory effects on IRG secretion but failed to elicit any significant effect on the epinephrine inhibited IRI release either in basal state or during the metabolic stimulus. These results suggest that, at least in the rat, the adrenergic stimulation of IRG release is mediated through a beta 1 receptor.

Effects of alpha and beta adrenergic blockade on hepatic glucose balance before and after oral glucose. Role of insulin and glucagon

In conscious dogs, phentolamine infusion significantly increased fasting portal vein insulin, glucagon, and decreased net hepatic glucose output and plasma glucose. Propranolol significantly decreased portal vein insulin, portal flow, and increased hepatic glucose production and plasma glucose. Phentolamine, propranolol, and combined blockade reduced glucose absorption after oral glucose. alpha, beta, and combined blockade abolished the augmented fractional hepatic insulin extraction after oral glucose. Despite different absolute amounts of glucose absorbed and different amounts of insulin reaching the liver, the percent of the absorbed glucose retained by the liver was similar for control and with alpha- or beta blockade, but markedly decreased with combined blockade. Our conclusions are: (a) phentolamine and propranolol effects on basal hepatic glucose production may predominantly reflect their action on insulin and glucagon secretion; (b) after oral glucose, alpha- and beta-blockers separately or combined decrease glucose release into the portal system; (c) net hepatic glucose uptake is predominantly determined by hyperglycemia but can be modulated by insulin and glucagon; (d) direct correlation does not exist between hepatic delivery and uptake of insulin and net hepatic glucose uptake; (e) alterations in oral glucose tolerance due to adrenergic blockers, beyond their effects on glucose absorption, can be, to a large extent, mediated by their effects on insulin and glucagon secretion reflecting both hepatic and peripheral glucose metabolism.

Physical performance and serum potassium under chronic beta-blockade

Various publications have described a beta 2-receptor regulated potassium transport system in the cellular membrane of human skeletal muscle. To examine the suggestion that serum potassium alterations are among the causes of premature muscular fatigue during physical exercise under pharmacological blockade of beta-receptors, we have compared the influence of sustained blockade with a beta 1-selective blocker and a nonselective beta-blocker on the levels of serum potassium before, during and after a physical exercise test. 63 healthy physical education students received in random order and under double blind conditions either 100 mg Metoprolol (beta 1-selective) or 80 mg Propranolol (non-selective), or placebo daily for 3 months. Serum potassium was measured before, during (at 150 Watt and at the end of exercise) and after a bicycle exercise with a stepwise increase in work loads. After three months of beta-blocker treatment serum potassium levels during exercise were significantly higher than in control subjects receiving the placebo, and it took longer for the serum potassium levels to return to the resting level in the beta-blocker treated subjects. At rest, however, the levels were not found to be statistically different. In the subjects receiving Propranolol the post-exercise serum potassium levels were higher than in the subjects receiving Metoprolol. Three days after cessation of the medication these differences were no longer perceptible. Our findings confirm the existence of a beta-receptor regulated potassium transport system in human skeletal muscle and indicate that the transmembranous potassium transport in human skeletal muscle is predominantly regulated via beta 2-receptors, although beta 1-receptors seem also to be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of prazosin and alphamethyldopa on blood lipids and lipoproteins in hypertensive patients

The effects of prazosin and alphamethyldopa on blood lipids and lipoproteins were assessed in 20 patients with mild or moderate arterial hypertension. Parameters measured included serum cholesterol (CHO), triglycerides (TG), high density lipoprotein-cholesterol (HDL-CHO), insulin (I), glucose (G), and non-esterified fatty acids (NEFA). Prazosin -4 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.6/17.2 (systolic/diastolic pressure) mmHg. There was a significant decrease in CHO (-5.8%), in I (-16.5%), and in NEFA (-3.0%), and a significant increase in HDL-CHO (+15.5%). Alphamethyldopa 250-750 mg/day for 6 weeks in hydrochlorothiazide-treated patients lowered blood pressure by 18.8/14.6 (systolic/diastolic pressure) mmHg, accompanied by a non-significant decrease in CHO and TG, and significant increases in HDL-CHO (+10.3%), G (+8.5%) and NEFA (+6.4%). Thus, prazosin appears to have a more beneficial effect on blood lipids and lipoproteins than alphamethyldopa.

Effects of (-)-(R)-1-(p-hydroxyphenyl)-2-[3,4-dimethoxyphenethyl)amino]ethanol (TA-064), a new cardiotonic agent, on circulating parameters of carbohydrate and lipid metabolism in the rat

Effects of the new cardiotonic and selective beta 1-adrenergic agonist TA-064, (-)-(R)-1-(p-hydroxyphenyl)-2-[(3,4-dimethoxyphenethyl)amino] ethanol, on circulating concentrations of glucose, lactate, free fatty acids (FFA), glycerol, cyclic AMP and the pancreatic hormones insulin (IRI) and glucagon (IRG) were examined in rats. TA-064, administered orally or intraperitoneally at the dose of 10 mg/kg (ca. 50 times the therapeutic dose) or higher, caused a slight transient rise followed by a persistent lowering of blood glucose concentrations, but it did not affect blood lactate levels at all. The same treatment with TA-064 elevated the concentrations of blood FFA, glycerol and plasma IRI and IRG. These changes induced by TA-064 were inhibited by pretreatment with propranolol (a non-selective beta-adrenergic antagonist) and practolol (a selective beta 1-adrenergic antagonist). The non-selective beta-adrenergic agonist isoproterenol and the selective beta 2-adrenergic agonist terbutaline elevated both blood glucose and lactate when administered intraperitoneally. They also brought about sustained rises in blood glycerol and plasma IRI, but only transiently increased the plasma IRG level. The cardiotonic agent prenalterol, claimed to be a selective beta 1-agonist, elevated blood glucose, lactate, and glycerol only slightly, and plasma IRI significantly, but it had no effect on plasma IRG. The cardiotonic agents dobutamine and amrinone also elevated blood glucose. Thus, TA-064 is unique among the beta-adrenergic and other cardiotonic agents in that it produces sustained hypoglycemia while it has no lactacidemic effect. Since this hypoglycemic action of TA-064 was always preceded by a rise in plasma IRI and abolished in streptozotocin-diabetic rats, we conclude that increased secretion of pancreatic insulin and the lack of hyperglycemic action are responsible for the hypoglycemia by high doses of TA-064.

Serum glucose levels during long-term observation of treated and untreated men with mild hypertension. The Oslo study

Serum glucose levels, triglyceride levels, and body weight are reported from a controlled drug trial in men, aged 40 to 49, with uncomplicated mild hypertension. The drug treatment started with hydrochlorothiazide alone, and methyldopa was added when necessary. If side effects occurred, methyldopa was replaced by propranolol. No detailed advice about diet, smoking, or weight reduction was given to any group. The untreated control subjects had a small increase in serum glucose levels during five years, from 6.08 to 6.21 mmol/liter. Those treated with hydrochlorothiazide alone and those treated with hydrochlorothiazide plus methyldopa had a small increase in serum glucose levels of the same order as that in the control subjects. However, those receiving the thiazide/propranolol combination experienced a sizeable increase in glucose levels, from 5.96 to 6.53 mmol/liter (p less than 0.001). This increase was significantly greater than the increase in the other groups (p less than 0.001). The thiazide/propranolol group also showed a significant increase in serum triglyceride levels (p less than 0.05). There was no difference in serum potassium levels in the different drug groups. The results indicate that moderate thiazide doses do not have significant effects on serum glucose levels in this age group. Propranolol in combination with thiazide seems to increase the level of serum glucose.

Adrenergic effects on plasma levels of glucagon, insulin, glucose and free fatty acids in rabbits--influences of selective blocking drugs

Species differences concerning the effects of alpha- and beta-receptor stimulation on glucagon release and carbohydrate metabolism have been reported. The aim of the present study was to investigate how the subtypes of alpha- and beta-receptors regulate the plasma levels of glucagon, insulin, glucose and free fatty acids in fasted rabbits. Epinephrine-induced 1) hyperglucagonaemia, 2) hypoinsulinaemia and 3) hyperglycaemia were significantly inhibited by alpha-2 receptor blockade (yohimbine), and not influenced by alpha-1 receptor blockade (prazosin). Isoproterenol-induced 1) hyperglucagonaemia was not affected by beta-1 or beta-2 receptor blockade, 2) hyperinsulinaemia was inhibited by a lower dose of beta-2 (ICI 118.551) than beta-1 receptor blockade (metoprolol), 3) hyperglycaemia was inhibited by beta-2 receptor blockade and 4) increases in the plasma levels of free fatty acids were blocked by beta-1 receptor blockade. It is concluded that in fasted rabbits: 1) plasma levels of glucagon are mainly increased by alpha-2 receptor stimulation, 2) plasma levels of insulin are decreased by alpha-2 receptor stimulation, and increased more by beta-2 than by beta-1 receptor stimulation, 3) plasma levels of glucose are increased by alpha-2 and beta-2 receptor stimulation and 4) the plasma levels of free fatty acids are increased by beta-1 receptor 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.

Metabolic and hormonal responses to exhaustive supramaximal running with and without beta-adrenergic blockade

The metabolic and hormonal responses to exhaustive short-term supramaximal exercise were studied in 10 male physical education students. The exercise task was a single bout of running on the treadmill at 22 km X h-1 and 7.5% slope. It was performed with single oral doses of 100 mg Bupranolol (non-selective beta-blockade), 100 mg Metoprolol (beta-1-selective blockade), and placebo. Arterialized capillary and venous blood were sampled until 30 min post exercise. Time to exhaustion was 52.0 +/- 2.6, 47.6 +/- 2.0, and 46.0 +/- 1.9 s in the control, Metroprolol, and Bupranolol experiments. At cessation of exercise, adrenaline and noradrenaline were grossly elevated in all three conditions. Lactate and glucose increased markedly, this being accompanied by increasing insulin in the control and Metoprolol, but not the Bupranolol trials. Glycerol increased moderately, while FFA were depressed. Growth hormone showed a delayed increase at 15 and 30 min post exercise. Cortisol was unaffected by exercise. beta-blockade reduced the increases of lactate, glucose, glycerol, insulin, and growth hormone, exaggerated the depression of FFA and had no effect on cortisol. The results demonstrate that the strong sympatho-adrenal response to exercise of this nature is a major determinant of the increase of glucose at cessation of exercise. The hyperglycemia in concert with beta-2-adrenergic stimulation leads to elevation of insulin. Furthermore, lipolysis is controlled by beta-adrenergic stimulation. The delayed increase of growth hormone seems to be triggered by the declining glucose level during recovery.

Can the biochemical responses to a beta 2-adrenoceptor stimulant be used to assess the selectivity of beta-adrenoceptor blockers?

The extent to which beta-adrenoceptor blocking drugs counteract the biochemical responses to an infusion of terbutaline, a beta 2-adrenoceptor agonist, has been investigated. In this study the beta 1-selectivity of metoprolol was compared with the non-selective beta-adrenoceptor blocker propranolol. The hypokalaemia produced by an infusion of terbutaline was reduced by low dose (50 mg) and high dose (200 mg) metoprolol and by low dose (40 mg) and high dose (160 mg) propranolol. The effects of propranolol on terbutaline induced hypokalaemia were more marked than those of metoprolol at both low dose (P = 0.01) and high dose (P = 0.05). Furthermore low dose metoprolol had less effect than high dose metoprolol (P = 0.05). The serum potassium appeared to rise slightly after propranolol. Low and high doses of both beta-adrenoceptor blockers markedly reduced the terbutaline-induced hyperglycaemia, but the differences between the two drugs were not statistically significant.

[Catecholamines, GH, cortisol, glucagon, insulin, and sex hormones in exercise and beta 1-blockade (author's transl)]

The effects of beta-1-adrenergic blockade (100 mg metoprolol) on metabolism in exercise was examined in 14 healthy males who worked for 50 min on a treadmill at 65% of their maximal exercise capacity. The tests were carried out in a double blind fashion. Glucose and lactate were determined in arterialized capillary blood, free fatty acids, glycerol, growth hormone, cortisol, glucagon, insulin, testosterone, and estradiol in serum, and adrenaline and noradrenaline in plasma. Lactate and glucose were not significantly affected by beta-1-adrenergic blockade, free fatty acids and glycerol were reduced by 50% and 30% respectively as compared with the unmedicated condition. Adrenaline and noradrenaline levels were increased by 104% and 54% respectively, growth hormone by 60%, cortisol by 72%, and glucagon by 36% when compared with the control experiments. Insulin and estradiol were unaffected, testosterone was depressed by 21% under medication. The results demonstrate that during prolonged exercise beta-1-adrenergic blockade depresses lipolysis. Energetic deficiency is prevented by counter-regulatory increases of various hormones. Consequently, from the metabolic point of view there is no indication of impairment of prolonged exercise capacity under beta-1-adrenergic blockade.

A trial of metoprolol in hypertensive insulin-dependent diabetic patients

Twenty-four insulin-dependent, hypertensive diabetic patients were treated with a beta 1-selective blocking agent (metoprolol) to evaluate its influence on diabetic state and arterial blood pressure (BP). Two groups were delineated after exclusion of one patient. Twelve patients (group A) obtained normotension with metoprolol alone, whilst 11 (group B) required concomitant treatment with thiazides, 7 of them both with thiazides and hydralazine. BP fell significantly in group B, by 15% (p less than 0.01), compared with pretreatment levels. Postprandial blood glucose levels, glucose excretion and insulin requirements were unchanged during treatment in all patients. Neither quantitative nor qualitative changes in the recognition of the effects of insulin were observed by 15 diabetics familiar with this sensation. Side-effects were few. One episode of severe hypoglycaemia, probably unrelated to the beta-blockade, was encountered. We suggest that antihypertensive treatment with metoprolol is a reasonable alternative in the treatment of hypertensive insulin-dependent diabetic patients.

The effect of acebutolol and propranolol on the hypoglycaemic action of glibenclamide

1 The effect of acebutolol, a relatively selective beta-adrenoceptor blocking drug and propranolol, a non-selective one, on the hypoglycaemic action of glibenclamide after an oral glucose load has been investigated in a group of maturity-onset diabetic patients. 2 Glibenclamide significantly reduced the blood glucose levels and both acebutolol and propranolol, at therapeutic doses, were found to modify this action significantly. 3 The effect of acebutolol was slightly less than that of propranolol. The difference was not statistically significant. 4 The modes of action of sulphonylureas are reviewed and it is suggested that beta-adrenoceptor blockers may modify their effect on insulin release. This appears to be a drug interaction rather than an effect of beta-adrenoceptor blockade on glucose tolerance.

Cardiovascular and metabolic effects of terbutaline

Terbutaline is a selective beta 2 agonist used predominantly in the treatment of asthma. Since beta-mediated responses increase heart rate, dilate peripheral arteries, modify carbohydrate metabolism and the uptake of electrolytes into cells, the administration of terbutaline might be expected to produce widespread effects. In this study the intravenous administration of 0.5 mg terbutaline over 60 mn has been shown to produce marked changes without upsetting the volunteers. Heart rate, systolic blood pressure and plasma glucose all increase; diastolic pressure and serum potassium decrease. The data suggests that the terbutaline infusion may be a useful tool for the investigator. The results also quantitate some of the side effects which may result from the intravenous administration of a therapeutic dose of terbutaline given to asthmatics or to pregnant women to reduce uterine activity and delay childbirth.

Metabolic effects of prenalterol in healthy volunteers

The effect of the beta 1-adrenoceptor agonist prenalterol on the metabolic parameters glucose, lactate, free fatty acids and serum-insulin were studied in 8 healthy volunteers. Prenalterol was administered intravenously in geometrically increasing doses from 5 to 80 micrograms/kg. The only metabolic effect of prenalterol that could be proved was a significant dose-dependent rise in FFA-concentration. The stimulating effect of prenalterol on lipolysis was significant not only at the time points of maximal effect following each injection, but also 30 min later. Serum-insulin-concentration and glucose- and lactate-concentration failed, however, to show a significant rise after prenalterol administration. This behaviour is a strong indication of a beta 1-selectivity of prenalterol over the whole dose range given.