Epinephrine and norepinephrine are cleared through beta-adrenergic, but not alpha-adrenergic, mechanisms in man

Studies on the insulin-antagonistic effect of catecholamines in normal man. Evidence for the importance of beta 2-receptors

The insulin-antagonistic effect of adrenaline was studied in seven healthy subjects with the euglycaemic clamp technique using two insulin infusion rates (40 and 1200 mU X (m2)-1 min-1). The adrenergic receptor mediating the adrenaline effect was characterized by concomitant infusion of propranolol (beta 1 + beta 2-antagonist) or metoprolol (beta 1-antagonist). Each subject was studied four times (placebo, adrenaline, adrenaline + propranolol, adrenaline + metoprolol). Glucose turnover was measured with D(3-3H)-glucose. Similar plasma insulin levels were reached in all studies with the two insulin infusion rates (mean; placebo 51 +/- 3 and 7421 +/- 337 mU/l respectively). Glucose production was completely inhibited by the low insulin level during placebo infusion. Adrenaline antagonized this effect so that a significant glucose production was seen at the low but not at the high insulin level. Propranolol, but not metoprolol, reversed this insulin-antagonistic effect of adrenaline. Glucose utilization increased from 2.53 +/- 0.17 to 7.28 +/- 0.88 mg X kg-1 X min-1 during placebo when the insulin levels were increased from 4 +/- 0.3 to 51 +/- 3 mU/l. Increasing the insulin levels 150-fold to approximately 7500 mU/l only doubled the glucose utilization (14.68 +/- 1.14 mg X kg-1 X min-1). Adrenaline induced a pronounced inhibition of glucose utilization at both insulin levels (78% and 37% inhibition respectively). Propranolol, but not metoprolol, prevented this effect of adrenaline. Thus, physiological adrenaline levels exert a pronounced insulin-antagonistic effect which is mediated by beta 2-receptor stimulation. The inhibitory effect on glucose uptake is maintained even at high insulin levels when hepatic glucose production is completely abolished.

The effect of 8 weeks treatment with the calcium antagonist felodipine on blood pressure, heart rate, working capacity, plasma renin activity, plasma angiotensin II, urinary catecholamines and aldosterone in patients with essential hypertension

The effect of 8 weeks treatment with the calcium antagonist felodipine--a new long-acting dihydropyridine derivative--in a dose of 10 mg twice daily was studied in 10 male patients with essential hypertension, WHO grade I-II, aged 25-62 years. Diastolic blood pressure was reduced in supine and upright position. Systolic blood pressure was reduced only in the upright position. Heart rate was unchanged in the supine and decreased in the upright position. During dynamic exercise blood pressure was reduced. The maximal working capacity decreased, whereas the maximal heart rate attained was unchanged. Twenty-four hour urinary noradrenaline excretion, plasma renin activity and 24 h urinary aldosterone excretion were increased. Plasma angiotensin II and 24 h urinary adrenaline excretion were unchanged. In conclusion, felodipine is an effective long-acting blood pressure lowering drug with minor side effects. After 8 weeks on felodipine treatment heart rate was not increased, although the activity of the sympathetic nervous system and the renin-aldosterone system seemed enhanced.

Glucoregulation during exercise: hypoglycemia is prevented by redundant glucoregulatory systems, sympathochromaffin activation, and changes in islet hormone secretion

During mild or moderate nonexhausting exercise, glucose utilization increases sharply but is normally matched by increased glucose production such that hypoglycemia does not occur. To test the hypothesis that redundant glucoregulatory systems including sympathochromaffin activation and changes in pancreatic islet hormone secretion underlie this precise matching, eight young adults exercised at 55-60% of maximal oxygen consumption for 60 min on separate occasions under four conditions: (a) control study (saline infusion); (b) islet clamp study (insulin and glucagon held constant by somatostatin infusion with glucagon and insulin replacement at fixed rates before, during and after exercise with insulin doses determined individually and shown to produce normal and stable plasma glucose concentrations prior to each study); (c) adrenergic blockage study (infusions of the alpha- and beta-adrenergic antagonists phentolamine and propranolol); (d) adrenergic blockade plus islet clamp study. Glucose production matched increased glucose utilization during exercise in the control study and plasma glucose did not fall (92 +/- 1 mg/dl at base line, 90 +/- 2 mg/dl at the end of exercise). Plasma glucose also did not fall during exercise when changes in insulin and glucagon were prevented in the islet clamp study. In the adrenergic blockade study, plasma glucose declined initially during exercise because of a greater initial increase in glucose utilization, then plateaued with an end-exercise value of 74 +/- 3 mg/dl (P less than 0.01 vs. control). In contrast, in the adrenergic blockade plus islet clamp study, exercise was associated with glucose production substantially lower than control and plasma glucose fell progressively to 58 +/- 7 mg/dl (P less than 0.001); end-exercise plasma glucose concentrations ranged from 34 to 72 mg/dl. Thus, we conclude that: (a) redundant glucoregulatory systems are involved in the precise matching of increased glucose utilization and glucose production that normally prevents hypoglycemia during moderate exercise in humans. (b) Sympathochromaffin activation, perhaps sympathetic neural norepinephrine release, plays a primary glucoregulatory role by limiting glucose utilization as well as stimulating glucose production. (c) Changes in pancreatic islet hormone secretion (decrements in insulin, increments in glucagon, or both) are not normally critical but become critical when catecholamine action is deficient. (d) Glucoregulation fails, and hypoglycemia can develop, both when catecholamine action is deficient and when changes in islet hormones do not occur during exercise in humans.

Pathogenesis of the dawn phenomenon in patients with insulin-dependent diabetes mellitus. Accelerated glucose production and impaired glucose utilization due to nocturnal surges in growth hormone secretion

The early-morning increase in insulin requirements of patients with insulin-dependent diabetes mellitus (IDDM) has been referred to as the "dawn phenomenon." To determine the roles of growth hormone levels and sympathoadrenal activity in this phenomenon, we studied six subjects with IDDM on four occasions during a constant overnight infusion of insulin. In control experiments (infusion of insulin alone), plasma glucose increased from 98 +/- 5 mg per deciliter at midnight to 225 +/- 36 at 8:00 a.m. (P less than 0.001), glucose production increased by 65 per cent (P less than 0.001), and glucose clearance decreased by 50 per cent (P less than 0.001). When nocturnal surges in growth hormone secretion were prevented by infusion of somatostatin plus replacement glucagon, neither plasma glucose levels nor glucose production increased significantly, and glucose clearance did not decrease. When nocturnal surges in growth hormone secretion were simulated by hourly intravenous injections of growth hormone (15 to 100 micrograms) during infusion of somatostatin and glucagon, plasma glucose levels and glucose production increased and glucose clearance decreased to values observed in control experiments. During combined alpha- and beta-adrenergic blockade (phentolamine and propranolol), values for plasma glucose, glucose production, and glucose utilization were not significantly different from those in control experiments. Increases in plasma glucose were significantly correlated with peak plasma growth hormone concentrations (r = 0.58, P less than 0.01). We conclude that nocturnal surges in growth hormone secretion are primarily responsible for the dawn phenomenon in patients with IDDM.

Adrenergic effects on renal secretion of epidermal growth factor in the rat

Urinary epidermal growth factor (EGF) has been demonstrated recently to originate from the kidneys. The present study was undertaken to investigate the adrenergic and cholinergic influence on secretion of renal EGF. beta-Adrenergic agonists increased the level of urinary EGF, while propranolol, a beta-adrenergic blocking agent, decreased basal and beta-adrenergic stimulated total output of urinary EGF. Acetylcholine and the anticholinergic agent atropine had no effect on the output of EGF in urine. Also chemical sympathectomy induced by 6-hydroxydopamine reduced the urinary output of EGF. None of the experimental groups had a median serum concentration above the detection limit of the assay. The present study shows that secretion of renal EGF is under the influence of the sympathetic nervous system and release of EGF is stimulated by activation of beta-adrenergic receptors in the kidneys.

Role of hepatic autoregulation in defense against hypoglycemia in humans

To assess the role of hepatic autoregulation in defense against hypoglycemia, we compared the effects of complete blockade of glucose counterregulation with those of blockade of only neurohumoral counterregulation during moderate (approximately 50 mg/dl) and severe (approximately 30 mg/dl) hypoglycemia induced by physiologic hyperinsulinemia during subcutaneous infusion of insulin in normal volunteers. Compared with observations in control experiments, neurohumoral counterregulatory blockade (somatostatin, propranolol, phentolamine, and metyrapone), during which identical moderate hypoglycemia was achieved using the glucose clamp technique, resulted in suppressed glucose production (0.62 +/- 0.08 vs. 1.56 +/- 0.07 mg/kg per min at 12 h, P less than 0.01) and augmented glucose utilization (2.17 +/- 0.18 vs. 1.57 +/- 0.07 mg/kg per min at 12 h, P less than 0.01). Complete blockade of counterregulation (neurohumoral blockade plus prevention of hypoglycemia) did not further enhance the suppressive effects of insulin on glucose production. However, when severe hypoglycemia was induced during neurohumoral counterregulatory blockade, glucose production was nearly two times greater (1.05 +/- 0.05 mg/kg per min at 9 h) than that observed during complete counterregulatory blockade (0.58 +/- 0.08 mg/kg per min at 9 h, P less than 0.01) and that observed during mere neurohumoral blockade with moderate hypoglycemia (0.59 +/- 0.06 mg/kg per min at 9 h, P less than 0.01). These results demonstrate that glucose counterregulation involves both neurohumoral and hepatic autoregulatory components: neurohumoral factors, which require only moderate hypoglycemia for their activation, augment glucose production and reduce glucose utilization; hepatic autoregulation requires severe hypoglycemia for its activation and may thus serve as an emergency system to protect the brain when other counterregulatory factors fail to prevent threatening hypoglycemia.

The effects of epinephrine on norepinephrine release in essential hypertension

The effects of endogenous epinephrine (E), released by glucagon injection, and exogenously infused E on plasma norepinephrine (NE) and cardiovascular responses before and after beta-blockade were studied in patients with essential hypertension and in age-matched normotensive controls. The resting plasma NE and E levels were significantly higher in the borderline hypertensive subjects (NE: 251 +/- 21 pg/ml [SEM], p less than 0.005; E: 57 +/- 5, p less than 0.05, n = 18) than in controls (NE: 129 +/- 12; E: 39 +/- 5, n = 18). An intravenous injection of glucagon (1.0 mg) induced a transient rise of both plasma catecholamine levels and blood pressure in every subject studied. Plasma E levels rose transiently and returned to the basal levels by 20 minutes after the injection, whereas plasma NE levels showed a more prolonged rise over 20 minutes. beta-Blockade with propranolol did not affect the plasma E response to glucagon, but inhibited the prolonged rise of plasma NE levels. An intravenous infusion of exogenous E (1.25-1.50 micrograms/min) for 30 minutes caused an apparent rise of both plasma NE levels and blood pressure, which lasted more than 60 minutes after stopping the E infusion. Propranolol did not affect the time course of plasma E but again inhibited the prolonged rise of both plasma NE levels and blood pressure. No significant differences could be observed in the cardiovascular or plasma NE responses to glucagon or to E infusion between normal and hypertensive subjects. These findings lend support to the view that plasma E can act physiologically as a sustained stimulator of presynaptic beta-adrenergic receptors, which leads to an enhanced NE release from peripheral sympathetic nerve terminals and a rise of blood pressure in humans.

Central nervous system mechanisms in blood pressure control

Much of our knowledge about the CNS control of blood pressure is derived from animal studies using techniques such as intracerebroventricular administration of drugs, stereotactic ablation of specific brain nuclei, and biochemical analysis of these nuclei. These methods have identified numerous specific brain nuclei in the brain stem and a meshwork of interconnecting neurones involved in cardiovascular control. The main neurotransmitter involved is noradrenaline but recent interest has focused on several laterally situated nuclei which are capable of synthesizing adrenaline. Centrally acting antihypertensive drugs are thought to act by stimulating central alpha 2-adrenoceptors either by the parent drug itself (clonidine) or via the formation of an active metabolite (alpha-methyldopa). This leads to decreased peripheral sympathetic activity and a hypotensive response but the latter is often attained at the expense of central side-effects such as drowsiness or dry mouth. The mechanism of the antihypertensive effect of beta-blockers remains uncertain although the balance of evidence is against a central effect. The central administration of propranolol causes decreased peripheral sympathetic activity in animals, but plasma catecholamine levels are little altered by beta-blockers in man. In equipotent antihypertensive doses, central alpha-agonists cause a much greater reduction in plasma noradrenaline than beta-blockers.

Mechanisms of action and the clinical pharmacology of beta-adrenergic blocking drugs

At present more than 20 beta-adrenergic blocking drugs are commercially available in Western Europe, and six are available in the United States. The clinical indications for their usage include hypertension, arrhythmias, ischemic heart disease, thyrotoxicosis, migraine headaches, glaucoma, and anxiety states. We will review the mechanisms suggested for the antihypertensive action of beta-adrenergic blocking drugs as well as these agents' clinical pharmacologic aspects. In general, the pharmacodynamic effects of the beta blocking drugs are quite similar, yet the properties of biotransformation, including pharmacokinetics, tend to be distinguishing features.

Catecholamine physiology in the ovine fetus. I. Gestational age variation in basal plasma concentrations

Fifty-five ewes with chronically catheterized singleton gestations were studied to assess changes in basal concentrations of fetal catecholamines with increasing gestational age. All pregnancies were time dated, and measurements of catecholamines were conducted at least 5 days after placement of fetal catheters when fetal metabolic parameters had normalized. Plasma concentrations of catecholamines were measured by radioenzymatic assay. Additionally, fetal heart rate (FHR) and corrected mean blood pressure were analyzed in 32 of the fetuses for correlation with plasma levels of catecholamines. Multiple regression analysis revealed significant inverse correlations of fetal plasma concentrations of catecholamines with gestational age, as follows: norepinephrine (p less than 0.001), epinephrine (p less than 0.05), and dopamine (p less than 0.01). FHR correlated inversely with gestational age (p less than 0.001) and positively with circulating levels of norepinephrine (p less than 0.001).

The effect of adrenergic blockade on glucose-induced thermogenesis

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

Catecholamine physiology in ovine fetus. II. Metabolic clearance rate of epinephrine

This study measured the metabolic clearance rate (MCR) of epinephrine (E) in 13 chronically catheterized fetal lambs between 120 and 145 days gestation. The E-MCR was determined by a constant infusion method at an E infusion rate of 0.1 microgram/kg estimated fetal wt. Fetal and maternal arterial blood samples were taken for measurements of catecholamine levels, pH, blood gases, and glucose. There was a significant positive correlation between gestational age and E-MCR (r = 0.87, P less than 0.001). The E production rate in fetuses less than 132 days (n = 6) (1,234 +/- 301 pg/min) was not significantly different from fetuses greater than or equal to 132 days (n = 7) (1,195 +/- 242). Catecholamine infusion resulted in a decrease in pH from a control value of 7.37 +/- 0.01 to 7.31 +/- 0.01 by 15 min of infusion, but there were no significant changes in fetal heart rate or blood pressure. The mean fetal plasma glucose concentration increased 45% above base line at 15 and 20 min and 65% above base line by 30 min of catecholamine infusion. After 60 min of infusion plasma norepinephrine (NE) increased from 380 +/- 60 to 520 +/- 75 pg/ml and plasma dopamine from 100 +/- 20 to 240 +/- 50 pg/ml (both P less than 0.05). These results indicate that E-MCR increases with maturation in the absence of a change in basal E production.

The effects of acute or chronic ingestion of propranolol or metoprolol on the metabolic and hormonal responses to prolonged, submaximal exercise in hypertensive men

We have studied the effects of single oral doses of, and of 28 days treatment with, placebo, propranolol or metoprolol, on the metabolic and hormonal responses to prolonged exercise in hypertensive men. Blood glucose levels fell during exercise on all occasions. No additional effects of the beta-adrenoceptor antagonists, compared to placebo, were observed. The exercise-induced increase in plasma potassium was enhanced after a single dose of propranolol or metoprolol, and also after chronic treatment with propranolol. Chronic treatment with either drug led to an increase in plasma potassium levels at rest. The growth hormone response to exercise was potentiated by a single dose of metoprolol or propranolol, and after chronic treatment with the drugs. A single dose of propranolol (but not metoprolol) was associated with a marked increase in plasma cortisol and adrenaline levels during exercise. After chronic treatment no such increase occurred. In both the acute and chronic phases of the study, blood lactate levels were higher during exercise in the presence of either propranolol or metoprolol compared to placebo, whereas non-esterified fatty acid levels were lower. A single dose of metoprolol produced a significantly greater reduction in blood glycerol levels during exercise than a single dose of propranolol. After chronic treatment, both propranolol and metoprolol produced similar reductions in blood glycerol levels during exercise. After a single dose, both drugs significantly augmented the increase in plasma noradrenaline levels during exercise. A similar effect was seen after chronic treatment.

Epinephrine supports the postabsorptive plasma glucose concentration and prevents hypoglycemia when glucagon secretion is deficient in man

We hypothesized that adrenergic mechanisms support the postabsorptive plasma glucose concentration, and prevent hypoglycemia when glucagon secretion is deficient. Accordingly, we assessed the impact of glucagon deficiency, produced by infusion of somatostatin with insulin, without and with pharmacologic alpha- and beta-adrenergic blockade on the postabsorptive plasma glucose concentration and glucose kinetics in normal human subjects. During somatostatin with insulin alone mean glucose production fell from 1.5 +/- 0.05 to 0.7 +/- 0.2 mg/kg per min and mean plasma glucose declined from 93 +/- 3 to 67 +/- 4 mg/dl over 1 h; glucose production then increased to base-line rates and plasma glucose plateaued at 64-67 mg/dl over 2 h. This plateau was associated with, and is best attributed to, an eightfold increase in mean plasma epinephrine. It did not occur when adrenergic blockade was added; glucose production remained low and mean plasma glucose declined progressively to a hypoglycemic level of 45 +/- 4 mg/dl, significantly (P less than 0.001) lower than the final value during somatostatin with insulin alone. These data provide further support for the concept that maintenance of the postabsorptive plasma glucose concentration is a function of insulin and glucagon, not of insulin alone, and that adrenergic mechanisms do not normally play a critical role. They indicate, however, that an endogenous adrenergic agonist, likely adrenomedullary epinephrine, compensates for deficient glucagon secretion and prevents hypoglycemia in the postabsorptive state in humans. Thus, postabsorptive hypoglycemia occurs when both glucagon and epinephrine are deficient, but not when either glucagon or epinephrine alone is deficient, and insulin is present.

Adrenergic vasoconstriction as a cause of inadequate hypotensive response to beta-adrenergic blockade

This overview is concerned with the causes of nonresponsiveness to the hypotensive action of beta-adrenergic blocking drugs. The overall hemodynamic response, i.e., a secondary decrease in peripheral vascular resistance, is unrelated to the primary decrease in cardiac output. The reduction in vascular resistance may be triggered by mechanisms residing in the central nervous system, the arterial baroreceptor area, or the prejunctional beta-receptor. None of these mechanisms seem to be entirely responsible. Studies in responders vs nonresponders tend to equate nonresponsiveness with alpha-adrenoceptor-mediated vasoconstriction. Although circulating catecholamines are relatively poor indices of sympathetic activity, studies focusing on the renal-neural area appear to show clearly differential profiles between responders and nonresponders. Such findings, in relation to experimental data on the renal nerves as selective neural amplifiers, may provide a renewed interpretation of the centrally mediated hypotensive mechanism of beta-adrenergic blockade.

Mechanisms of postprandial glucose counterregulation in man. Physiologic roles of glucagon and epinephrine vis-a-vis insulin in the prevention of hypoglycemia late after glucose ingestion

The transition from exogenous glucose delivery to endogenous glucose production late after glucose ingestion is not solely attributable to dissipation of insulin and, therefore, must also involve factors that actively raise the plasma glucose concentration--glucose counterregulatory factors. We have shown that the secretion of two of these, glucagon and epinephrine, is specific for glucose ingestion and temporally related to the glucose counterregulatory process. To determine the physiologic roles of glucagon and epinephrine in postprandial glucose counterregulation, we produced pharmacologic interventions that resulted in endogenous glucagon deficiency with and without exogenous glucagon replacement, adrenergic blockade, and adrenergic blockade coupled with glucagon deficiency starting 225 min after the ingestion of 75 g of glucose in normal subjects. Also, we assessed the effect of endogenous epinephrine deficiency alone and in combination with glucagon deficiency late after glucose ingestion in bilaterally adrenalectomized subjects. Glucagon deficiency resulted in nadir plasma glucose concentrations that were approximately 30% lower (P less than 0.01) than control values, but did not cause hypoglycemia late after glucose ingestion. This effect was prevented by glucagon replacement. Neither adrenergic blockade nor epinephrine deficiency alone impaired the glucose counterregulatory process. However, combined glucagon and epinephrine deficiencies resulted in a progressive fall in mean plasma glucose to a hypoglycemic level late after glucose ingestion; the final glucose concentration was 40% lower (P less than 0.02) than the control (epinephrine deficient) value in these patients, and was nearly 50% lower (P less than 0.001) than the control value and approximately 30% lower (P less than 0.05) than the glucagon-deficient value in normal subjects. We conclude (a) the transition from exogenous glucose delivery to endogenous glucose production late after glucose ingestion is the result of the coordinated diminution of insulin secretion and the resumption of glucagon secretion. (b) Epinephrine does not normally play a critical role in this process, but enhanced epinephrine secretion compensates largely and prevents hypoglycemia when glucagon secretion is deficient.

Coordinated responses of glucogenic hormones to central glucopenia: the role of the sympathoadrenal system

In normal humans glucagon plays a primary role in promoting glucose recovery from hypoglycemia, glucagon deficiency is largely compensated for by enhanced epinephrine secretion, and recovery from hypoglycemia fails to occur only in the absence of both glucagon and epinephrine. Defective glucose counterregulation is exemplified by patients with insulin-dependent diabetes. Although most such patients have deficient glucagon secretory responses to hypoglycemia, they counterregulate adequately because of intact epinephrine secretion. Some patients, however, become defenseless against hypoglycemia because of combined deficiencies of glucagon and epinephrine.

The effect of captopril and propranolol on the responses to posture and isometric exercise in patients with essential hypertension

The effects of captopril and propranolol on blood pressure, heart rate and plasma noradrenaline, renin and aldosterone, and on the responses to changes in posture and to isometric exercise were measured in patients with essential hypertension. During placebo administration blood pressure, heart rate and plasma noradrenaline rose on standing and during isometric exercise. The rise in diastolic blood pressure during isometric exercise correlated significantly with the rise in plasma noradrenaline. During captopril treatment blood pressure was significantly lower than during placebo administration when the patients were lying, standing or sitting, but the reduction during isometric exercise was not significant. Plasma renin increased, but heart rate, plasma noradrenaline and plasma aldosterone remained unchanged. The acute changes in blood pressure, heart rate and plasma noradrenaline produced by standing and isometric exercise during captopril treatment were similar to those during placebo administration. During propranolol treatment diastolic blood pressure was significantly lower than during placebo administration when the patients were lying, standing or sitting and during isometric exercise. Heart rate also fell. Plasma noradrenaline during standing, sitting and isometric exercise was significantly greater than during placebo administration. The changes in plasma noradrenaline measured during propranolol treatment with the patients supine were negatively correlated with noradrenaline values obtained during placebo administration: plasma noradrenaline fell in patients with higher, and increased in those with lower, initial concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term beta-receptor blockade--adrenergic and metabolic response to surgery and neurolept anaesthesia

Twenty-six patients on chronic (greater than 3 months) beta-receptor blocking therapy due to ischaemic heart disease and/or hypertension were randomly distributed to a 4-day gradual withdrawal (n = 13) or a continuation of ordinary therapy until a planned cholecystectomy under neurolept anaesthesia (n = 13). Plasma-adrenaline, -noradrenaline, -potassium, -glycerol, -FFA, -insulin and b-glucose were determined perioperatively. The metabolic response to surgery was as expected with hyperglycaemia and depressed insulin levels, which did not differ significantly between the two groups of patients. Plasma-catecholamines showed the highest mean values during emergence from anaesthesia. Plasma-adrenaline and -potassium were constantly highest in the beta-receptor-blocked patients, who also showed indices of a relatively depressed lipolysis compared to patients in whom beta-receptor blockers had been withdrawn. These discrepancies between withdrawal versus continuation of preoperative beta-receptor blockade seemed to be of small clinical importance and did not oppose the present view that beta-receptor blockers should generally be continued during surgery. However, findings in individual patients suggest that beta-receptor blockade may maintain hypoglycaemia in catabolic patients.

Catecholamines levels and parotid secretion in children with chronic atopic dermatitis

The purpose of this study was to evaluate the in vivo state of both branches of the autonomic nervous system in children with chronic atopic dermatitis. In 15 patients, age 4 to 11, the following parameters were analyzed: (1) basal plasma levels of epinephrine, norepinephrine, and dopamine; (2) poststimulation (standing and i.v. furosemide administration); (3) basal urinary excretion of epinephrine, norepinephrine, and vainillin mandelic acid; (4) 30 min postfurosemide administration; (5) parotid secretory response to intraoral 0.1 m citric acid: flow rate, saliva pH, and concentrations of bicarbonate, chlorides, inorganic phosphates, total protein, and amylase activity. No differences in plasma and urinary basal levels of the catecholamines were observed. In response to standing, plasma norepinephrine from atopic children showed a greater increase than that seen in normal healthy children. From the salivary factors studied, no differences were found in parotid flow-rate, bicarbonates, chlorides, and inorganic phosphates. Protein concentration as well as amylase activity were significantly decreased in children with atopic dermatitis. These findings suggest that in atopic dermatitis, the beta-sympathetic mediated responses are impaired; on the other hand, parasympathetic mediated responses remain preserved.

Reduced pressor effect of angiotensin II and of noradrenaline in normal man following the oral administration of the calcium-antagonist nifedipine

The pressor response to both angiotensin II (5, 10 and 20 ng kg-1 min-1) and to noradrenaline (50, 100 and 200 ng kg-1 min-1) was reduced (P less than 0.05 to less than 0.005) in six healthy male subjects following the administration of the calcium-antagonist nifedipine (10 mg p.o.). Nifedipine induced a rise in basal plasma noradrenaline concentrations but did not alter the plasma concentrations of adrenaline, dopamine, renin and aldosterone. A slight reduction in the angiotensin II induced rise of plasma aldosterone by nifedipine was observed after the administration of the largest dose of angiotensin II only (P less than 0.05). The reduced responsiveness towards pressor agents following oral nifedipine is in keeping with the known antihypertensive effect of calcium-antagonistic drugs and could provide a concept for the effectiveness of these drugs in hypertensive crisis.

Elevated plasma noradrenaline in response to beta-adrenoceptor stimulation in man

1 Dose-dependent increments of plasma noradrenaline were observed during graded infusions of (±)isoprenaline (3.5-35 ng kg^-1 min^-1 i.v.) in seven normal subjects and in ten subjects with borderline hypertension. At the highest dose of isoprenaline, noradrenaline rose by 166 ± 16 pg/ml in normals and by 169 ± 34 pg/ml in hypertensives (mean ± s.e. mean).

2 In the subjects with borderline hypertension isoprenaline infusions were repeated after 7 days of treatment with (±)propranolol (320 mg/day, divided into 4 doses) and subsequently after 7 days of treatment with (±)atenolol (100 mg/day) 2-3 h after the morning dose of β-adrenoceptor blocker. The dose-response curve for plasma noradrenaline was shifted to higher doses of isoprenaline by a factor of 4 by atenolol and the heart rate response was similarly shifted. The heart rate response was shifted by a factor of 16 by propranolol, but plasma noradrenaline did not change after isoprenaline under propranolol treatment, even when isoprenaline was given at doses high enough to induce increments of heart rate similar to those without β-adrenoceptor blocker treatment.

3 In the subjects with borderline hypertension mean and diastolic intra-arterial pressures fell at the highest dose of isoprenaline by 9 ± 2 and 13 ± 2 mm Hg respectively. These effects were antagonized by propranolol and not by atenolol.

4 The observed rise in plasma noradrenaline after isoprenaline might have been caused by baro-reflex-stimulation of central sympathetic outflow. The isoprenaline-induced decrease in mean arterial pressure, however, was small. Moreover pulse pressure rose and this tends to suppress rather than stimulate baroreflex-mediated sympathetic activity. Activation of presynaptic β-adrenoceptors, allegedly of the β₂-subtype, is known to facilitate noradrenaline release upon nerve stimulation of isolated tissues. Our results lend support to the hypothesis that such a facilitatory mechanism is also operative in intact man.

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.

How intrinsic sympathomimetic activity modulates the haemodynamic responses to beta-adrenoceptor antagonists. A clue to the nature of their antihypertensive mechanism

1 A survey has been made of the literature on acute and long-term haemodynamic effects of ten different β-adrenoceptor antagonists.

The β-adrenoceptor blockers are: pindolol, practolol, alprenolol, oxprenolol, acebutolol, penbutolol, metoprolol, atenolol, propranolol and timolol. The total numbers of patients included in this review are 396 patients in 41 acute studies and 410 patients in 36 long-term studies.

2 The effects of β-adrenoceptor blockers on the concentrations of plasma noradrenaline have also been reviewed. Ten studies including 110 patients on non-ISA-β-adrenoceptor blockers and eight studies including 116 patients on pindolol are presented.

3 In the acute studies (i.e. 15-90 min) arterial pressure was lowered by 1-7% and in the long-term studies (i.e. 3 days-5 years) by 6-17%.

4 The degree of cardio-depression induced by the various β-adrenoceptor blockers was inversely correlated with their pharmacologically defined quantity of intrinsic sympathomimetic activity (ISA) both in acute and in long-term studies.

5 In the acute studies the increments in peripheral vascular resistance were directly correlated with the degree of cardio-depression. This suggests that a fall in arterial pressure immediately after administration of a β-adrenoceptor blocker is prevented by increased vasoconstrictor nerve activity mediated through the arterial baroreflex.

6 The compensatory response of vascular resistance to cardio-depression was similar for β₁-selective and non-selective blockers, thereby indicating that extra-junctional vascular β-receptors are relatively unimportant for maintaining basal vascular tone.

7 In the long-term studies the correlation between changes in cardiac output and changes in vascular resistance was shifted to a lower level of vascular resistance. This means that the onset of blood pressure reduction during β-adrenoceptor blockade was associated with a fall in vascular resistance at any level of cardiac output. Thus vascular resistance was higher during treatment with a non-ISA-β-adrenoceptor blocker than during treatment with an ISA-β-adrenoceptor blocker.

8 The level of vascular resistance ultimately attained during treatment with the various β-adrenoceptor blockers appears to be inversely related to their effects on plasma renin activity.

9 The concentration of noradrenaline in plasma rose by approximately 30% during treatment with non-ISA-β-adrenoceptor blockers and fell by more than 30% after pindolol.

10 There is evidence that under propranolol, which reduces cardiac output and hepatic blood flow, the plasma noradrenaline clearance is diminished. Since noradrenaline is mainly cleared from the circulation by the lungs and by the liver, and since pindolol has no effect on cardiac output and hepatic blood flow, one may expect the plasma noradrenaline clearance not to be diminished by pindolol.

11 The reported effects of β-adrenoceptor blockers on plasma noradrenaline may indicate that the release of neurotransmitter is diminished, but in the case of non-ISA-β-adrenoceptor blockers this effect is not reflected by a decreased concentration of noradrenaline in plasma, because its clearance is also reduced.

12 The hypotensive effect of β-adrenoceptor blockers appears to be independent of blockade of postjunctional cardiac-β-receptors, juxtaglomerular-β-receptors and extrajunctional vascular β-receptors. This indicates that blockade of β-receptors at other sites (i.e. centrally and/or prejunctionally) is more important.