Beta blockade and diabetes mellitus: effect of oxprenolol and metoprolol on the metabolic, cardiovascular, and hormonal response to insulin-induced hypoglycemia in normal subjects

Heart Failure in Diabetes Mellitus: An Updated Review

Diabetes mellitus (DM) and heart failure (HF) are comorbid conditions associated with significant morbidity and mortality worldwide. Despite the availability of novel and effective therapeutic options and intensive glycaemic control strategies, mortality and hospitalisation rates continue to remain high and the incidence of HF persists. In this review, we described the impact of currently available glucose-lowering therapies in DM with a focus on HF clinical outcomes. Non-conventional modes of management and alternative pathophysiological mechanisms with the potential for therapeutic targeting are also discussed.

Interdisciplinary approach to compensation of hypoglycemia in diabetic patients with chronic heart failure

Diabetes mellitus is a chronic disease requiring lifelong control with hypoglycemic agents that must demonstrate excellent efficacy and safety profiles. In patients taking glucose-lowering drugs, hypoglycemia is a common cause of death associated with arrhythmias, increased thrombus formation, and specific effects of catecholamines due to sympathoadrenal activation. Focus is now shifting from merely glycemic control to multifactorial approach. In the context of individual drugs and classes, this article reviews interdisciplinary strategies evaluating metabolic effects of drugs for treatment of chronic heart failure (CHF) which can mask characteristic hypoglycemia symptoms. Hypoglycemia unawareness and cardiac autonomic neuropathy are discussed. Data suggesting that hypoglycemia modulates immune response are reviewed. The potential role of gut microbiota in improving health of patients with diabetes and CHF is emphasized. Reports stating that nondiabetic CHF patients can have life-threatening hypoglycemia associated with imbalance of thyroid hormones are discussed. Regular glycemic control based on HbA1c measurements and adequate pharmacotherapy remain the priorities in diabetes management. New antihyperglycemic drugs with safer profiles should be preferred in vulnerable CHF patients. Multidrug interactions must be considered. Emerging therapies with reduced hypoglycemia risk, telemedicine, sensor technologies, and genetic testing predicting hypoglycemia risk may help solving the challenges of hypoglycemia in CHF patients with diabetes. Interdisciplinary work may involve cardiologists, diabetologists/endocrinologists, immunologists, gastroenterologists, microbiologists, nutritionists, imaging specialists, geneticists, telemedicine experts, and other relevant specialists. This review emphasizes that systematic knowledge on pathophysiology of hypoglycemia in diabetic patients with CHF is largely lacking and the gaps in our understanding require further discoveries.

Risk of Cardiovascular Events in Patients With Diabetes Mellitus on β-Blockers

Although the use of β-blockers may help in achieving maximum effects of intensive glycemic control because of a decrease in the adverse effects after severe hypoglycemia, they pose a potential risk for the occurrence of severe hypoglycemia. This study aimed to evaluate whether the use of β-blockers is effective in patients with diabetes mellitus and whether its use is associated with the occurrence of severe hypoglycemia. Using the ACCORD trial (Action to Control Cardiovascular Risk in Diabetes) data, we performed Cox proportional hazards analyses with a propensity score adjustment. The primary outcome was the first occurrence of a cardiovascular event during the study period, which included nonfatal myocardial infarction, unstable angina, nonfatal stroke, and cardiovascular death. The mean follow-up periods (±SD) were 4.6±1.6 years in patients on β-blockers (n=2527) and 4.7±1.6 years in those not on β-blockers (n=2527). The cardiovascular event rate was significantly higher in patients on β-blockers than in those not on β-blockers (hazard ratio, 1.46; 95% confidence interval, 1.24-1.72; P<0.001). In patients with coronary heart disease or heart failure, the cumulative event rate for cardiovascular events was also significantly higher in those on β-blockers than in those not on β-blockers (hazard ratio, 1.27; 95% confidence interval, 1.02-1.60; P=0.03). The incidence of severe hypoglycemia was significantly higher in patients on β-blockers than in those not on β-blockers (hazard ratio, 1.30; 95% confidence interval, 1.03-1.64; P=0.02). In conclusion, the use of β-blockers in patients with diabetes mellitus was associated with an increased risk for cardiovascular events.

Intensive Glycemic Therapy in Patients With Type 2 Diabetes on β-Blockers

OBJECTIVE

Recent studies have suggested that β-blockers may decrease the adverse influence of hypoglycemia and reduce hypoglycemia-associated cardiac arrhythmias and death. We evaluated whether intensive glycemic therapy in patients with diabetes receiving treatment with β-blockers showed beneficial effects for the prevention of cardiovascular events without increased mortality compared with a standard glycemic therapy.

RESEARCH DESIGN AND METHODS

We used Action to Control Cardiovascular Risk in Diabetes (ACCORD) trial data to assess the risks of cardiovascular events, all-cause death, and cardiovascular death in patients with diabetes receiving treatment with β-blockers (n = 3,079) and not receiving treatment with β-blockers (n = 7,145) using Cox proportional hazard models.

RESULTS

In patients receiving treatment with β-blockers, the cumulative event rates for cardiovascular events were significantly lower in the intensive therapy group compared with the standard therapy group (hazard ratio [HR] 0.81; 95% CI 0.67-0.97; P = 0.02), whereas those rates in patients not receiving treatment with β-blockers were not significantly different (HR 0.92; 95% CI 0.78-1.09; P = 0.36). Conversely, the cumulative event rates for all-cause and cardiovascular deaths in patients receiving treatment with β-blockers were not significantly different between the standard therapy and intensive therapy groups (all-cause death: HR 1.08; 95% CI 0.83-1.42; P = 0.54; cardiovascular death: HR 1.05; 95% CI 0.72-1.51; P = 0.79), whereas in patients not receiving treatment with β-blockers, the event rates were significantly higher in the intensive therapy group compared with the standard therapy group (all-cause death: HR 1.25; 95% CI 1.02-1.52; P = 0.02; cardiovascular death: HR 1.43; 95% CI 1.03-1.98; P = 0.03).

CONCLUSIONS

Intensive glycemic therapy may be effective in patients with type 2 diabetes receiving treatment with β-blockers.

Effectiveness of Prior Use of Beta-Blockers for Preventing Adverse Influences of Severe Hypoglycemia in Patients With Diabetes: An Observational Study

The study aimed to identify predictors of severe acute hypertension (≥ 180/110 mmHg) during severe hypoglycemia and to assess the efficacy of prior use of catecholamine-blocking agents for preventing adverse influences in diabetic patients with severe hypoglycemia. We performed a retrospective study between January 2006 and March 2012 to assess diabetic patients with severe hypoglycemia at a single center in Japan. Severe hypoglycemia was defined as the presence of any hypoglycemic symptoms that required the medical assistance of another person after visiting the emergency room by ambulance. Multivariate logistic regression analysis was performed to identify possible predictors of severe hypertension due to severe hypoglycemia and to assess whether prior use of alpha- or beta-blockers is beneficial for the prevention of severe hypertension in diabetic patients with severe hypoglycemia. Multivariate adjustments were made for age, sex, preexisting hypertension, history of ischemic heart disease, blood glucose level upon arrival, estimated GFR, and prior use of alpha- or beta-blockers. A total of 59,602 patients who visited the emergency room were screened and 352 diabetic patients with severe hypoglycemia were enrolled. Incidences of severe hypertension before and at 3 and 6 hours after the initiation of antihypoglycemic treatment were 21.3%, 6.7%, and 0% in patients with type 1 diabetes (n = 61) and 38.8%, 18.2%, and 8.2% in patients with type 2 diabetes (n = 291), respectively. Aging was positively (odds ratio [OR], 1.02; 95% confidence interval [CI], 1.00-1.03; P = 0.02) and female sex was negatively (OR, 0.50; 95% CI, 0.29-0.86; P = 0.01) associated with occurrence of severe hypertension during severe hypoglycemia. In addition, prior use of beta-blockers was negatively associated with occurrence of severe hypertension during severe hypoglycemia using multivariate logistic regression analysis (OR, 0.31; 95% CI, 0.11-0.83; P = 0.02). None of the patients with prior use of beta-blockers had hypokalemia (<3.0 mEq/L). Prior use of beta-blockers may prevent adverse influences such as severe hypertension and hypokalemia during severe hypoglycemia in diabetic patients.

Adrenergic blockade and hypoglycaemia

The metabolic effects of beta-adrenoceptor blocking agents during hypoglycaemia in patients prone to hypoglycaemia are of interest as diabetics are often treated with these drugs because of hypertension or angina pectoris. Compared with non-diabetics these patients also have impaired glucose compensation after hypoglycaemia, partly secondary to deficient release of glucagon. This makes the diabetics more dependent on adrenergic mechanisms to recover from low blood glucose concentrations. Non-selective beta-adrenoceptor blockade (propranolol) significantly impairs the glucose recovery rate after hypoglycaemia in insulin dependent diabetics, whereas selective beta-adrenoceptor blockade (metoprolol) does not have this side effect. The mechanism of the effect of propranolol is probably an attenuation of the gluconeogenesis secondary to deficient release of the important gluconeogenic substrates lactate and glycerol.

Effect of metoprolol and alprenolol on the metabolic, hormonal, and haemodynamic response to insulin-induced hypoglycaemia in hypertensive, insulin-dependent diabetics

Insulin hypoglycaemia was induced three times in 6 insulin-dependent, hypertensive diabetics: before instituting antihypertensive long-term treatment and after obtaining a satisfactory blood pressure with either alprenolol or metoprolol given in a randomized order. The blood glucose concentration (1.6-1.9 mmol/l) at which the hypoglycaemia necessitated intravenous administration of glucose was almost identical on all three occasions. During hypoglycaemia the systolic and diastolic blood pressures increased significantly by a mean maximal rise of 27/14 mmHg on alprenolol treatment, but remained unchanged on metoprolol. The responses of adrenaline, noradrenaline, cortisol, and growth hormone did not differ significantly on the three occasions. None of the beta-adrenergic drugs counteracted the early hormone defence mechanisms in hypoglycaemia and the signs of hypoglycaemia were not masked. The haemodynamic response was altered only by the non-selective (alprenolol) and not by the selective beta-adrenergic blocking agent (metoprolol).

Adrenergic effects on adrenocortical cortisol response to incremental exercise to exhaustion

This study evaluated the influence of adrenergic factors on the cortisol response to maximal exercise in endurance-trained men. This was achieved by testing healthy young men during exercise while varying both the condition of beta-adrenergic blockage and the presence of a well-controlled simulated competitive environment to simulate activity of the sympatho-adrenal systems. Subjects (n = 10) performed maximal exercise (running) to exhaustion on a treadmill during four conditions: (1) placebo non-competitive [PNon] (2) after administration of 80 mg propranolol non-competitive [betaNon] (3) in a simulated competition after a placebo intake [PCom], and (4) in a simulated competition after propranolol intake [betaCom]. Blood samples were obtained before (pre-) and 3 min after (post-) exercise and assayed for cortisol (C). The data were analyzed with a multi-factorial repeated measures ANCOVA procedure. Statistical analysis revealed a significant three-way interaction for the drug versus competition versus sampling time effects (P < 0.05). Post-hoc tests revealed that the pre-exercise cortisol values did not differ significantly among the conditions. Cortisol did increase from pre- to post-exercise in all experimental conditions (P < 0.01), and the magnitudes of increase in the PCom, betaNon and betaCom conditions were greater than that of the PNon condition. Furthermore, the cortisol increases for both beta-blockage conditions post-exercise (betaNon, betaCom) did not differ from one another (P > 0.05). The findings suggest beta-adrenergic blockage and competitive conditions enhance the exercise cortisol response. In combination, however, these conditions do not act in an additive fashion. This suggests that perhaps there may be two separate influences or mechanisms (i.e., excitatory, inhibitory) on the adrenergic control of adrenocortical function, or a sympathetic compensation for beta-blockage during exhaustive maximal exercise. Furthermore, the data suggests a possible "ceiling" on the hypothalamic-pituitary-adrenal axis response to exercise in endurance-trained men.

Systemic and local adrenergic regulation of muscle glucose utilization during hypoglycemia in healthy subjects

Adrenergic responses are crucial for hypoglycemic recovery. Epinephrine increases glucose production, lipolysis, and peripheral insulin resistance as well as blood flow and glucose delivery. Sympathetic activation causes vasoconstriction and reduces glucose delivery. To determine the effects of alpha- and beta-adrenergic activity on muscle glucose uptake during hypoglycemia, we studied forearm blood flow (FBF) (plethysmography), arteriovenous glucose difference (AV-diff), and forearm glucose uptake (FGU) during insulin infusion with 60 min of euglycemia followed by 60 min of hypoglycemia. Twelve healthy subjects (27 plus minus 5 years of age) were randomized to intravenous propranolol (IV PROP, 80 microg/min), intravenous phentolamine (IV PHEN, 500 microg/min), intra-arterial propranolol (IA PROP, 25 microg/min), intra-arterial phentolamine (IA PHEN, 12 microg/min per 100 ml forearm tissue), and saline (SAL). FBF increased during hypoglycemia with SAL (P < 0.001) but not with IA or IV PROP. FGU (P = 0.015) and AV-diff (P = 0.099) fell during hypoglycemia with IA PROP but not with IV PROP. FBF increased during hypoglycemia with IA and IV PHEN (P < 0.005). AV-diff fell during hypoglycemia with IA and IV PHEN (P < 0.01), but FGU was unchanged. Blood pressure fell (P < 0.001), and adrenergic and neuroglycopenic symptoms increased with IV PHEN (P < 0.01). Thus, systemic but not local propranolol prevents a decrease in forearm glucose extraction during hypoglycemia, suggesting that epinephrine increases peripheral muscular insulin resistance through systemic effects. alpha-Adrenergic activation inhibits vasodilation and helps maintain brain glucose delivery.

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.

Hypertension in obesity may reflect a homeostatic thermogenic response

Systemic hypertension of mild to moderate degree is often associated with obesity. The hypothesis is that over-eating leads to increased sympathetic activity targeted at the peripheral vasculature as well as other tissues in an attempt (that in many cases may be futile) to stimulate facultative thermogenesis and burn-off the excess energy. This hypothesis represents an important modification of one proposed by Landsberg and is supported by: 1) recent observations that carbohydrate feeding to humans specifically increases muscle sympathetic vasoconstrictor activity in the peroneal nerve, and 2) studies with animal models in which active vasoconstriction in the limbs and elsewhere is associated with marked increases in oxygen consumption (energy expenditure).

Beta-adrenoceptor blockade and hypoglycaemia. A randomised, double-blind, placebo controlled comparison of metoprolol CR, atenolol and propranolol LA in normal subjects

1. The effect of 1 week of treatment with propranolol LA (160 mg), atenolol (100 mg) and metoprolol CR (100 mg) on awareness of and the physiological responses to moderate hypoglycaemia were compared with placebo using a randomised, cross-over design in 12 healthy volunteers. 2. All three beta-adrenoceptor antagonists reduced resting heart rate, systolic blood pressure and heart rate responses to submaximal exercise compared with placebo. 3. Under hyperinsulinaemic (60 mu m-2 min-1) clamp conditions, at a blood glucose of 2.5 mmol l-1, atenolol prevented the rise in systolic and atenolol and metoprolol CR prevented the fall in diastolic blood pressure usually associated with hypoglycaemia. At this level of hypoglycaemia, the expected increase in heart rate was inhibited by atenolol but not metoprolol CR. Pre-treatment with propranolol LA resulted in a significant pressor response and a bradycardia during hypoglycaemia. In addition the normal increase in finger tremor was abolished by propranolol LA. 4. During hypoglycaemia all three beta-adrenoceptor blockers augmented sweating compared with placebo but hypoglycaemic symptoms, awareness and slowing of reaction time were the same with drugs and placebo. 5. The rise in plasma adrenaline and other counter-regulatory hormones during hypoglycaemia was enhanced by beta-adrenoceptor blockade. 6. We conclude that beta-adrenoceptor antagonists modify the physiological and hormonal responses to, but do not adversely affect awareness of, moderate hypoglycaemia in healthy volunteers.

Beta-blockers in hypertensive non-insulin-dependent diabetics: comparison between penbutolol and propranolol on metabolic control and response to insulin-induced hypoglycemia

In a single blind randomized study the effects of a 4-week administration of propranolol (160 mg/day) and penbutolol (40 mg/day) on metabolic control and insulin-induced hypoglycemia were tested in 8 non-insulin-dependent diabetics with diastolic blood pressure between 95 and 110 mmHg. The recovery from hypoglycemia was not delayed by either drug; hypoglycemic nadir and Conard's K did not change significantly. Symptoms of hypoglycemia were inhibited to a lesser extent and pulse rate decrease was lower after penbutolol vs baseline (65 +/- 2.4 vs 77 +/- 2.4 beats/min, p less than 0.01) than after propranolol vs baseline (61 +/- 1.06 vs 77 +/- 2.4 beats/min p less than 0.001). Both drugs produced similar and significant effects on blood pressure both systolic and diastolic. There were no significant effects on fasting plasma glucose concentration, HbA1c, IRI, urinary C-peptide, triglycerides, total and HDL cholesterol and FFA. IRG decreased after penbutolol vs baseline 60 min after insulin injection (170 +/- 30.8 vs 125 +/- 15.4 pmol/l, p less than 0.05). These results indicate that the use of beta-blockers, in particular penbutolol, for mild to moderate hypertension may be considered the treatment of choice also in non-insulin-dependent diabetics at the therapeutic doses employed.

Early posthypoglycemic insulin resistance in man is mainly an effect of beta-adrenergic stimulation

The insulin effect following hypoglycemia was studied with the euglycemic clamp technique in seven healthy subjects. Following an initial euglycemic clamp hypoglycemia was induced and after glucose recovery a second clamp was performed. Glucose production (Ra) and utilization (Rd) were studied with [3-3H]glucose. Each subject was studied four times; during infusion of placebo, propranolol, somatostatin, and a control study where hypoglycemia was prevented. Hypoglycemia induced an insulin resistance with a lower steady state glucose infusion rate following the hypoglycemia during placebo as compared to the control study (2.5 +/- 0.5 and 4.8 +/- 1.0 mg/kg min, respectively, P less than 0.05). The insulin resistance was due to an attenuated insulin effect on both inhibition of Ra (impaired by 37%) and stimulation of Rd (impaired by 61%). The insulin-antagonistic effect was completely prevented by propranolol but only partly by somatostatin. Thus, early posthypoglycemic insulin resistance (2.5-3.5 h after hypoglycemia) is a sustained effect mainly due to beta-adrenergic stimulation.

The effect of selective beta adrenergic blockade on glucose-induced thermogenesis in man

We have previously shown that the increase in energy expenditure following glucose/insulin infusion is, in large part, mediated by the sympathetic nervous system and that this sympathetic component can be blocked by the nonselective beta-1, beta-2 antagonist propranolol. To examine which beta adrenergic receptor mediates this thermogenic response, we performed euglycemic insulin clamp studies in eight healthy control subjects with and without metoprolol at a dose known to block only the beta-1 adrenergic receptor. Basal glucose oxidation and energy expenditure were similar in the control and metoprolol groups. During the last hour of the insulin clamp study, glucose oxidation (3.06 +/- 0.25 v 2.92 +/- 0.21 mg/kg X min), total body glucose uptake (8.17 +/- 0.70 v 7.13 +/- 0.49 mg/kg X min), and nonoxidative glucose uptake (5.11 +/- 0.60 v 4.21 +/- 0.44 mg/kg X min) were not different in the control compared to the metoprolol group. However, the increment in energy expenditure was inhibited by 64% during metoprolol infusion (0.04 +/- 0.01 v 0.11 +/- 0.02 kcal/min, P less than 0.01). Glucose/insulin-induced thermogenesis was similarly reduced by metoprolol (2.56 +/- 0.81 v 5.04 +/- 0.74%, P less than 0.01). These results are quantitatively quite similar to those observed with propranolol. We conclude that the beta adrenergic nervous system and, specifically, the beta-1 receptor mediates the thermogenic response to glucose/insulin infusion.

Metoprolol. An updated review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy, in hypertension, ischaemic heart disease and related cardiovascular disorders

During the intervening years since metoprolol was first reviewed in the Journal (1977), it has become widely used in the treatment of mild to moderate hypertension and angina pectoris. Although much data have accumulated, its precise mechanisms of action in these diseases remain largely uncertain. Optimum treatment of hypertension and angina pectoris with metoprolol is achieved through dose titration within the therapeutic range. It has been clearly demonstrated that metoprolol is at least as effective as other beta-blockers, diuretics and certain calcium antagonists in the majority of patients. Although a twice daily dosage regimen is normally used, satisfactory control can be maintained in many patients with single daily doses of conventional or, more frequently, slow release formulations. Addition of a diuretic may improve the overall response rate in hypertension. Several controlled trials have studied the effects of metoprolol administered during the acute phase and after myocardial infarction. In early intervention trials a reduction in total mortality was achieved in one moderately large trial of prolonged treatment, but in another, which excluded patients already being treated with beta-blockers or certain calcium antagonists and where treatment was only short term, mortality was significantly reduced only in 'high risk' patients. Overall results with metoprolol have not demonstrated that early intervention treatment in all patients produces clinically important improvement in short term mortality. Thus, the use of metoprolol during the early stages of myocardial infarction is controversial, largely because of the requirement to treat all patients to save a small number at 'high risk'. This blanket coverage approach to treatment may be more justified during the post-infarction follow-up phase since it has been shown that metoprolol slightly, but significantly, reduces the mortality rate for periods of up to 3 years. Metoprolol is generally well tolerated and its beta 1-selectivity may facilitate its administration to certain patients (e.g. asthmatics and diabetics) in whom non-selective beta-blockers are contraindicated. Temporary fatigue, dizziness and headache are among the most frequently reported side effects. After a decade of use, metoprolol is well established as a first choice drug in mild to moderate hypertension and stable angina, and is beneficial in post-infarction patients. Further study is needed in less well established areas of treatment such as cardiac arrhythmias, idiopathic dilated cardiomyopathy and hypertensive cardiomegaly.

Beta-adrenoceptor-blocking drugs: current status and the significance of partial agonist activity

There is some evidence that partial agonism is an important property of beta-blocking drugs, and this property may be exploited to produce a new range of positive inotropic drugs. With the established beta-adrenoceptor-blocking drugs, the level of partial agonist activity is weak and the dose-response curve for this property is shallow. However, its absence appears to increase the likelihood of inducing bronchospasm and bradycardia, and drugs that lack intrinsic sympathomimetic activity appear more likely to be associated with rebound cardiac arrhythmias on cessation of treatment. The idea of a small level of hormone activity--in this case, catecholamine activity--being necessary to maintain normal cardiac and perhaps bronchial function is not new. Minimal doses of steroids are essential to maintaining the inotropic action of cardiac muscle. There is now enough accumulated evidence to suggest that a minimal degree of beta-adrenoceptor stimulation is also important for normal bronchial and cardiac function, and its absence increases the incidence of bradycardia and the risks of bronchospasm and rebound arrhythmias.

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

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