Regulation of human leukocyte beta receptors by endogenous catecholamines: relationship of leukocyte beta receptor density to the cardiac sensitivity to isoproterenol

Lymphocyte beta 2-adrenoceptors and plasma catecholamines in patients with cirrhosis

The hemodynamic response to propranolol in patients with cirrhosis is heterogeneous. In some patients, there is an expected decrease in portal pressure, whereas in others, portal pressure fails to decrease despite adequate beta-blockade. It has been suggested that this lack of response could be related to down-regulation of beta 2-adrenoceptors, promoted by the increased adrenergic activity frequently found in decompensated cirrhosis. The present study investigated this hypothesis by measuring the density and affinity of lymphocyte beta 2-adrenoceptors (L-beta 2-AR), an established index of beta 2-adrenoceptors in target organs, and the plasma levels of norepinephrine and epinephrine in a group of 32 patients with cirrhosis and portal hypertension. The portal pressure response to propranolol administration (0.1 mg/kg + 2 mg/h) was also investigated (n = 27). Patients with cirrhosis had increased norepinephrine levels (605 +/- 360 vs. 224 +/- 110 pg/mL in controls; P less than 0.001), but plasma epinephrine level was not increased (136 +/- 72 vs. 111 +/- 22 pg/mL in controls; NS). There were no differences between cirrhotic patients and controls in the density of L-beta 2-AR (1398 +/- 489 vs. 1278 +/- 356 receptors/cell; NS). Portal pressure decreased greater than 10% in 12 patients (responders) and less than 10% in the remaining 15 (nonresponders). Contrary to previous suggestions, there were no significant differences between responders and nonresponders in relation to the density of L-beta 2-AR (1362 +/- 527 vs. 1487 +/- 419 receptors/cell; NS), to the affinity of these receptors (0.15 +/- 0.27 vs. 0.13 +/- 0.12 nmol/L; NS), to the plasma levels of norepinephrine (661 +/- 508 vs. 621 +/- 256 pg/mL; NS), and to plasma epinephrine concentration (141 +/- 90 vs. 140 +/- 75 pg/mL; NS). These results show that the response of portal pressure to propranolol administration is neither related to the density and affinity of L-beta 2-AR nor to the plasma levels of norepinephrine and epinephrine. Thus, the determination of these parameters cannot substitute measurements of portal pressure to identify those patients with an adequate portal pressure response to propranolol treatment.

Beta-Adrenoceptor Modulation in a Case of Pure Autonomic Failure

In a patient with pure autonomic failure, exercise did not modify beta-adrenoceptor density, probably due to an insufficient increase in plasma catecholamines. Isoproterenol infusion increased the number of beta-adrenoceptor by only 17%. Since in control subjects an increased beta-adrenoceptor level was found, following both physical stress and isoproterenol infusion, we suggest that the lack of increased beta-adrenoceptor levels may contribute to the poor circulatory adjustments observed in autonomic dysfunction during activities involving the sympathetic nervous system.

Adrenergic hypersensitivity after beta-blocker withdrawal in hypertrophic cardiomyopathy

Withdrawal of beta-blocker therapy has been associated with the development of adrenergic hypersensitivity and adverse clinical effects in patients with coronary artery disease and hypertension. The aim of this study was to establish the occurrence and clinical significance of adrenergic hypersensitivity after abrupt withdrawal of long-term beta blockade in hypertrophic cardiomyopathy. Beta-adrenergic sensitivity was measured using the isoprenaline chronotropic dose25. Symptom assessment chronotropic dose25 calculation, bicycle exercise, echocardiography and Holter monitoring were performed while the patient received beta-blocker therapy and repeated on days 2, 4, 6, 8 (acute withdrawal period) and on day 21 after abrupt withdrawal. The study was terminated after 7 patients had been studied because all patients experienced a marked deterioration in symptoms and several clinical events had occurred. The chronotropic dose25 (mean +/- standard deviation) demonstrated beta 1-adrenergic hypersensitivity with a minimal value of 1.6 +/- 0.8 micrograms during the acute withdrawal period compared with 3.8 +/- 1.7 micrograms on day 21 (p = 0.003). Heart rates during rest and exercise showed an overshoot increase during the acute withdrawal period. The maximal 24-hour ventricular ectopic count was higher during the acute withdrawal period than during day 21 (p = 0.04). Of 3 patients with inducible outflow tract gradients, 2 developed resting gradients greater than 30 mm Hg during the acute withdrawal period. There was an increase in peak late filling velocity of mitral inflow after beta-blocker withdrawal. In conclusion, transient beta-adrenergic hypersensitivity occurs after beta-blocker withdrawal in hypertrophic cardiomyopathy and is associated with significant physiologic changes and adverse clinical consequences.

Are there beta-adrenergic receptor response differences between racial groups?

Beta-adrenergic receptor (BAR) agonists and antagonists are among the most widely used drugs in America today. This review highlights the importance of cross-racial studies in evaluating BAR effects because heterogeneity in pharmacologic response among humans exists. Clinicians and basic scientists in the drug development industry need to acknowledge racial differences in antihypertensive drug responses and prevent various racial groups from being underrepresented in clinical trials. This article reviews the influence of race on BAR responses with emphasis on blacks and whites. Information from patients with hypertension, healthy volunteers, and in vitro studies is presented.

Ethnic differences in drug disposition and responsiveness

Interethnic differences are important factors accounting for interindividual variations in drug responsiveness. However, these differences in drug response have been a relatively neglected area of investigation, so that similar doses are prescribed to different ethnic populations without consideration of interethnic pharmacokinetic and pharmacodynamic variation. With the increased recognition of genetically determined polymorphism in metabolising ability as an important factor in drug disposition, concern has developed for the importance of individualising drug dose to account for racial differences. The recognition of these differences in drug disposition and responses calls into question the failure of drug licensing authorities to demand information on dosage, efficacy and toxicity in different ethnic groups, and to accept data from limited ethnic groups such as Caucasians. This article reviews the evidence for ethnic differences in drug disposition and sensitivity and should encourage further investigations to elucidate the extent of such differences, their causes and their therapeutic impact.

Effects of chronic alpha 2-adrenoceptor blockade on platelet and lymphocyte adrenoceptor binding in normal volunteers

Platelet and lymphocyte adrenoceptor binding was measured in 12 healthy male volunteers before and after 22 days treatment with the alpha 2-adrenoceptor antagonist idazoxan 40 mg tds. Platelet alpha 2-adrenoceptor number assessed by the agonist 3H-UK 14304 [correction of UK 14303] was significantly increased following idazoxan, with a smaller increase in antagonist binding (3H-rauwolscine). Lymphocyte beta-adrenoceptor number was unaltered by idazoxan, although the variance within the sample was significantly increased. Plasma MHPG levels were significantly reduced by chronic idazoxan. These data indicate upregulation of the platelet alpha 2-adrenoceptor in response to chronic blockade and suggest that this may reflect a similar change in presynaptic alpha 2-adrenoceptors which regulate norepinephrine release.

Absence of correlations between plasma catecholamine levels and mononuclear leukocyte beta 2-adrenergic receptors in the elderly

To assess the effects of aging on catecholamine plasma levels and mononuclear leukocyte (NML) beta 2-adrenergic receptors and on the possible relationships between these two parameters, we evaluated two groups of human subjects: 18 elderly volunteers (age 65-70 years) and 13 young volunteers (age 21-35 years). Norepinephrine plasma levels were significantly higher in the elderly subjects compared to the younger ones (P less than 0.05), whereas plasma epinephrine levels were not different. Also MNL beta 2-adrenoceptor density was significantly higher in elderly subjects (P less than 0.05). The binding dissociation constants were not significantly different. In young subjects there was a significant (P less than 0.02), inverse relationship between receptor densities and plasma norepinephrine levels; this relationship was not present in elderly persons. Our data suggest that the increase in beta 2-adrenoceptors may be due to a compensatory phenomenon, owing to the reduced beta-adrenergic sensitivity observed in the elderly subjects; moreover, the regulation of beta-adrenoceptors by plasma catecholamines seems to be altered by aging.

Cholinergic-adrenergic balance: Part 2. Relationship between drug sensitivity and personality

Sensitivity to the centrally active cholinomimetic physostigmine varies dramatically among healthy individuals. The elucidation of the reasons for this variability could contribute to the understanding of the pathophysiology of affective disorders where a cholinergic supersensitivity has been demonstrated. Therefore, personality characteristics and habitual stress-coping strategies were related to sensitivity to physostigmine in eight healthy male volunteers. Cardiovascular and behavioral responses tended to be positively correlated with irritability and emotional liability. Passive, "helpless" strategies for coping with stress were positively related to these responses. The metabolic and neuroendocrine responses to physostigmine were generally unrelated to personality. In view of putative beta-adrenergic disturbances in depression, the responses to the peripheral beta 2-adrenergic agonist reproterol were studied. Irritability and emotionality tended to be positively correlated with cardiovascular responses to reproterol as well as with reductions of heart rate by the peripheral cholinomimetic neostigmine.

Cholinergic-adrenergic balance: Part 1. Relationship between central and peripheral sensitivities

Eight healthy volunteers were studied under double-blind conditions after acute challenge with the peripheral beta 2-agonist reproterol, either alone or combined with the peripheral indirect cholinomimetic neostigmine. Their responses were also studied after administration of the centrally active indirect cholinomimetic physostigmine. The beta-adrenergic rise in heart rate was cholinergically suppressed. The beta-adrenergic rise of plasma cyclic adenosine monophosphate (cAMP) was not cholinergically modulated, while that of plasma glucose tended to be cholinergically suppressed. Physostigmine induced an anergic-anhedonic syndrome accompanied by physiological, metabolic, and neuroendocrine stress phenomena. The beta-adrenergic and cholinergic sensitivities, respectively, of the various parameters investigated tended to be nonsignificantly intercorrelated. Only a limited portion of the variance was explained by drug effects. Sensitivity to neostigmine was completely unrelated to sensitivity to physostigmine. Thus, cholinergic sensitivity seems not to be decisive for the fine tuning of the highly complex regulatory systems studied and peripheral sensitivity not to be representative for the central one, at least if unselective drugs like neostigmine and physostigmine are used.

Alpha- and beta-adrenergic-receptor systems in bronchial asthma and in subjects without asthma: reduced mononuclear cell beta-receptors in bronchial asthma

We assessed the adrenergic-receptor system in individuals with bronchial hyperreactivity, beta-Adrenergic receptors on mononuclear cell membranes, alpha-adrenergic receptors on platelet membranes, and the cAMP response in these cell types to different stimuli, including platelet-activating factor (PAF), were determined. Studies were assessed in 10 subjects with mild asthma, six methacholine-sensitive subjects without asthma, and 10 normal subjects. The density and affinity of beta-receptors and alpha-receptors were determined by Scatchard analysis. Our findings were that (1) subjects with asthma had a significantly lower density of beta-receptors compared to normal subjects, (2) subjects with asthma had a significantly lower cAMP response to isoproterenol stimulation compared to the two other groups, (3) in subjects without asthma. PAF decreased the basal cAMP level and significantly inhibited the response to isoproterenol stimulation, (4) there was no difference in density and affinity of platelet alpha-receptors or in platelet cAMP responses to stimulation by alpha-agonists among these three groups, and (5) neither cAMP response or beta-receptor density on mononuclear cells were significantly correlated with pulmonary-function tests (FEV/FVC times 100), sensitivity to methacholine, or cold-air inhalation. These results suggest that patients with asthma may have a lower isoproterenol cAMP response and decreased density of beta-adrenergic receptors on mononuclear cells in the absence of beta-agonist therapy. It is speculated that release of PAF and other mediators secondary to allergen exposure, even in the absence of overt attacks of asthma, may inhibit the response to endogenous or exogenous beta-adrenergic agonists.

Adrenergic status in anxiety disorders: platelet alpha 2-adrenergic receptor binding, blood pressure, pulse, and plasma catecholamines in panic and generalized anxiety disorder patients and in normal subjects

In order to evaluate adrenergic function in anxiety disorders, platelet alpha 2-adrenergic binding parameters and supine and standing blood pressure, pulse, and venous plasma epinephrine and norepinephrine were determined in patients with panic attacks or generalized anxiety disorder and in normal subjects. The maximum number of binding sites (Bmax) for the partial agonist tritiated clonidine was significantly lower for both patient groups than for normal subjects, and the Bmax for the antagonist tritiated yohimbine was significantly lower for panic patients. There were no other substantive differences across groups. Prior exposure to psychotropic drugs might account for the results for clonidine binding, but not for yohimbine. The Bmax for clonidine was correlated with norepinephrine increases upon standing and, for panic patients, with the severity of full unexpected panic attacks. These data provide further evidence of adrenergic receptor abnormalities in people with anxiety disorders.

Time course of recovery of beta- and alpha 1-adrenoceptors in experimental asthma

1. The time course of recovery of reduced beta-adrenoceptors caused by ovalbumin (OA) challenge was investigated using guinea-pigs. 2. The effects of prednisolone on the recovery time course were also evaluated. 3. beta- and alpha 1-receptor assays were performed using lung membranes. Adenylate cyclase activity was also measured. 4. OA challenge reduced the number of beta-adrenoceptors by 35%, and a significant decrease (13%) persisted for 7 days. The number of beta-adrenoceptor recovered after 14 days. 5. OA challenge elevated the number of alpha 1-adrenoceptors. A significant increase (24%) was observed after 7 days, and it took a further 7 days for the recovery. 6. After OA challenge there was a significant decrease in adenylate cyclase activity after 7 days, which recovered after a further 7 days. 7. Inhalation of prednisolone accelerated the recovery of beta-adrenergic responsiveness, though it did not affect the recovery of the number of alpha 1-adrenoceptors. Prednisolone inhalation also elevated beta-adrenergic responsiveness in non-asthmatic subjects. 8. It is concluded that reduced beta-adrenergic responsiveness caused by OA challenge persisted for 7 days and recovered after a further 7 days. Steroid hormone increased beta-adrenoceptors.

Effects of calcium antagonists on beta-receptors of cultured cardiac myocytes isolated from neonatal rat ventricle

The effects of calcium antagonists (verapamil, diltiazem, and nicardipine) on beta-adrenergic receptors of cultured cardiac myocytes isolated from neonatal rat ventricle were studied with the hydrophilic ligand [3H]CGP-12177, which identifies cell surface-bound beta-receptors. The three calcium antagonists suppressed spontaneous beating of the myocytes, increased the number of beta-receptors, but did not alter the affinity (Kd). These effects were dose and time dependent. Verapamil (10(-6) M) increased the beta-receptor density by about 13% after 6 hours of incubation, and this increase in density reached a plateau of about 45% after 24 hours of incubation. beta-Receptor density increased by 15% with 5 x 10(-7) M and by 37% with 10(-6) M verapamil. The increased beta-receptors appeared to retain their normal function, as assessed by the increased spontaneous beating of the myocytes in response to applied isoproterenol. The increase in beta-receptors was abolished by colchicine but not by cycloheximide. When the calcium ion concentration of the medium was lowered to 0.1 mM, no significant change occurred in the density of beta-receptors compared with that in 1.8-mM Ca2+ medium. The results suggest that calcium antagonists increase beta-receptors by accelerating recycling by microtubules but not by decreasing the inward calcium current. Such effects of calcium antagonists may be clinically important and promise insight into the mechanism of the withdrawal phenomenon of calcium antagonists.

Sodium intake modulates the development of cardiac hypertrophy in two-kidney, one clip rats

Sodium homeostasis exerts a powerful influence on the cardiovascular system in normotensive and hypertensive animals. Previous studies indicate that factors other than blood pressure can influence cardiac hypertrophy. In the present experiments, we evaluated the effects of different sodium diets in the two-kidney, one clip hypertension model in the rat. After the renal artery had been clipped, the rats received a normal sodium (177 meq/kg), high sodium (517 meq/kg), and low sodium (7 meq/kg) diet during 4 weeks. The final blood pressure was almost the same in the three groups (normal sodium 170 +/- 12 mm Hg; low sodium 168 +/- 4 mm Hg; and high sodium 162 +/- 7 mm Hg). Sodium restriction significantly reduced the development of cardiac hypertrophy as compared with rats on normal or high sodium diets. Thus, ventricular weight and ventricular weight/body weight ratio were significantly higher in rats subjected to a normal or high sodium diet (p less than 0.01). The hypertrophied hearts of rats on normal and high sodium diets showed a larger increase in the number of cardiac beta-adrenergic receptors than those observed in hearts from low sodium diet, clipped rats. These results show that sodium modulates the development of cardiac hypertrophy in two-kidney, one clip hypertensive rats. Similarly, the cardiac beta-adrenergic receptors appear to be influenced by dietary sodium intake. A possible role of the sympathetic nervous system is suggested.

Beta-adrenoceptor responsiveness in hypertension: effects of dietary NaCl intake

1. Adrenergic responsiveness may be an important determinant of peripheral resistance in man. We have demonstrated that vascular beta-adrenergic responsiveness is reduced in young borderline hypertensive subjects. A parallel defect in beta-adrenergic mediated adenylyl cyclase activity and beta-adrenoceptor affinity for agonists also has been identified in lymphocytes from borderline hypertensive subjects. In contrast, it is unclear whether cardiac beta-adrenergic responsiveness is altered. 2. The reduction in lymphocyte and vascular beta-adrenergic responsiveness is corrected when hypertensive subjects are fed a low sodium chloride diet. This pattern of regulation differs from that seen in young normotensive subjects fed a low NaCl diet where either reduced or unchanged beta-adrenergic responsiveness has been reported. 3. These studies suggest a generalized defect in beta 2-adrenergic responsiveness in borderline hypertensive subjects and demonstrate important differences between normotensive and hypertensive subjects in the pattern of beta-adrenoceptor regulation mediated by dietary sodium intake. The mechanism by which dietary sodium modulates beta-adrenergic responsiveness is yet to be determined.

Downregulation of beta-adrenergic receptor-mediated function during sodium restriction in humans

Mononuclear leukocyte (MNL) beta 2-adrenergic receptor (beta 2-AR) binding and its linked adenylate cyclase sensitivity to isoproterenol were measured in nine healthy humans prior to and after 7 days of dietary sodium restriction to determine whether chronic physiological increases in plasma norepinephrine (NE) are associated with the downregulation of beta-AR-mediated function. Sodium restriction resulted in an increase in the plasma NE concentration (P less than 0.02) and decreases in MNL beta 2-AR density (P less than 0.001), affinity for antagonist (P less than 0.001), and adenylate cyclase sensitivity to isoproterenol (ANOVA, P less than 0.01). To determine whether this downregulation of MNL beta 2-AR-mediated function is related to the increased plasma NE concentration or to increased extravascular NE release, NE kinetics was assessed using compartmental analysis in each subject prior to and after sodium restriction. Sodium restriction caused a decrease in the plasma NE metabolic clearance rate (P less than 0.005) and in the volume of distribution of NE in the intravascular compartment (P less than 0.005), whereas the extravascular NE release rate was unchanged. Our data suggest that the downregulation of MNL beta 2-AR-mediated function in humans during dietary sodium restriction is a response to the increase in plasma NE.

Hemodynamic and beta-adrenergic receptor adaptations during long-term beta-adrenoceptor blockade. Studies with acebutolol, atenolol, pindolol, and propranolol in hypertensive patients

In an attempt to further clarify the mechanism of the maintenance of the antihypertensive effect of beta-adrenoceptor antagonists, the effects of four antagonists with different ancillary properties (acebutolol, atenolol, pindolol, and propranolol) on systemic and renal hemodynamics, body fluid volumes, hormones, and lymphocyte beta-adrenoceptor density were studied in four groups of 10 hypertensive patients. The patients were observed for 3 weeks during active treatment and for 2 weeks after withdrawal of treatment. At the end of the 3-week treatment period, the four drugs had an equal antihypertensive effect (fall in mean arterial pressure, 10-13%). Although renin activity was suppressed (60-70%) by all four drugs, changes in renin or pretreatment values of renin levels were not correlated with the fall in blood pressure. The drugs had no effect on plasma catecholamine concentrations or body fluid volumes. Despite similar antihypertensive effects among the four drugs, the changes in flow and resistance underlying the fall in blood pressure differed considerably. With pindolol, the fall in blood pressure was associated with a fall in vascular resistance (26 +/- 6%), whereas with propranolol, it was predominantly associated with a fall in cardiac output (11 +/- 7%). No significant changes in vascular resistance or cardiac output occurred with atenolol or acebutolol. The changes in renal blood flow and renal vascular resistance occurred in parallel with the changes in cardiac output and systemic vascular resistance. Plasma epinephrine concentration and pretreatment cardiac chronotropic responsiveness to isoproterenol appeared to be inversely correlated with lymphocyte beta-adrenoceptor density (Bmax) (r = -0.41 and -0.43, respectively). With pindolol, Bmax decreased maximally by 39 +/- 6%, and with propranolol, it increased by 51 +/- 17%. With both drugs, significant changes in Bmax were already present 24 hours after treatment. Furthermore, 1 week after withdrawal of treatment with pindolol, Bmax was still down-regulated, and cardiac chronotropic responsiveness was still decreased, whereas 1 week after withdrawal of propranolol, Bmax was still up-regulated, and cardiac chronotropic responsiveness was still increased. No changes in Bmax occurred with the beta 1-selective antagonists acebutolol and atenolol. Thus, despite an equal antihypertensive effect, the four beta-adrenoceptor antagonists appear to have dissimilar effects on cardiac output, renal blood flow, and lymphocyte beta-adrenoceptors. Changes in cardiac output, the circulating blood volume, or angiotensin-mediated vasoconstriction are factors unlikely to be crucial for the antihypertensive effect of beta-adrenoceptor antagonists. Therefore, interference with vasoconstrictor nerve activity through blockade of either central or peripheral prejunctional beta-adrenoceptors could be an alternative explanation of their blood pressure-lowering potential.

Human tissue adrenergic receptors are not predictive of responses to epinephrine in vivo

To test the hypotheses that adrenergic receptor and adenylate cyclase characteristics of easily accessible circulating cells reflect those of relatively inaccessible extravascular catecholamine target tissues in a subtype-specific fashion and that these characteristics predict responses to catecholamines in vivo, we studied 22 normal humans. Adrenergic receptors and their linked adenylate cyclase systems were measured in mononuclear leukocytes (MNL; beta 2), platelets (alpha 2), skeletal muscle membranes (beta 2), and fat cells (B1 and alpha 2) and compared with the responses to stepped, intravenous epinephrine infusions in vivo. MNL beta 2-adrenergic receptor densities (but not antagonist affinities) were correlated (r = 0.627; P less than 0.01) with skeletal muscle beta 2-adrenergic densities. However, other adrenergic receptor characteristics and basal and maximally stimulated adenosine 3',5'-cyclic monophosphate (cAMP) contents of MNL and all adrenergic receptor characteristics and cAMP contents of platelets were unrelated to the corresponding measurements in skeletal muscle and fat. Furthermore, there were no consistent relationships between tissue adrenergic receptor-adenylate cyclase characteristics and the chronotropic, diastolic depressor, lipolytic, ketogenic, glycemic, or glycogenolytic-glycolytic responses to epinephrine in vivo. Thus the data support the hypothesis that adrenergic receptor densities on circulating cells reflect those of extravascular target tissues in a subtype-specific fashion. On the other hand, the data do not support the hypothesis that physiological interindividual variation of adrenergic receptor characteristics is of sufficient magnitude to alter sensitivity to epinephrine in vivo.

Stereoselective disposition and pharmacologic activity of propafenone enantiomers

Propafenone is an antiarrhythmic drug that produces a variable degree of beta-blockade in humans and is administered as a racemate. To examine the relative contribution of the individual enantiomers to pharmacologic effects seen during treatment with propafenone, we assessed the steady-state plasma concentrations of (+)-S-propafenone and (-)-R-propafenone in seven patients who were on long-term oral therapy, and we evaluated the electrophysiologic and beta-blocking properties of both enantiomers in vitro. The metabolism of propafenone is known to be polymorphic and to cosegregate with that of debrisoquine-4-hydroxylation. Among five patients with the extensive metabolizer phenotype (EM), the ratio of the area under the plasma concentration-time curve of (+)-S-propafenone to (-)-R-propafenone was 1.73 +/- 0.15 (mean +/- SD). In the other two patients, who had the poor metabolizer phenotype (PM), the concentrations of both enantiomers were elevated but the S/R ratios were similar to those seen in patients with EM. In canine cardiac Purkinje fibers, both enantiomers produced similar frequency-dependent depression of maximum upstroke of phase 0. In contrast, the affinity of the human lymphocyte beta 2-adrenoceptor was approximately 100-fold greater for (+)-S-propafenone (Ki, 7.2 +/- 2.9 nM) than for the (-)-R-enantiomer (Ki, 571 +/- 141 nM). We conclude that during long-term oral therapy, propafenone undergoes stereoselective disposition in patients with either EM or PM. beta-Blockade during propafenone therapy is likely related to accumulation of (+)-S-propafenone.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of sympatho-adrenergic regulation at rest and of the adrenoceptor system in swimmers, long-distance runners, weight lifters, wrestlers and untrained men

The effects of different physical training regimes on the plasma catecholamine values at rest and the density and responsiveness of adrenergic receptors at rest were investigated. The changes during well-defined training periods of swimmers, long-distance runners, weight lifters and wrestlers were compared with untrained male volunteers. The training of swimmers and long-distance runners, building up endurance, resulted in a significantly lower basal plasma norepinephrine (NE) concentration and a significantly or possibly lower ratio NE:EPI (epinephrine). Both values indicated reduced sympathetic activity and resulted also in a significantly lower beta-receptor density and a higher alpha 2-receptor sensitivity compared with the other groups investigated. However, swimming-specific characteristics provoked labile hypertensive blood pressure regulation with an unchanged heart rate in swimmers. Static training of weight lifters, building up power, also led to a lower NE concentration compared with untrained subjects, whereas beta-receptor density was unchanged and alpha 2-receptor density and sensitivity were decreased. Elevated blood pressure values were observed in weight lifters and swimmers due to a reduced baroreceptor sensitivity. The dynamic training of wrestlers affected only basal heart rate and alpha 2-receptor sensitivity, both of which were decreased. Different kinds of physical training caused various adaptations of the basal activity of the autonomic nervous system in which adrenergic receptors also became adapted. In this context, the stronger adrenergic circulatory component of overall sympathetic activity at rest in swimmers and long-distance runners resulted in lower beta-receptor density, and the reduced noradrenergic component sensitized alpha 2-receptors.

Racial differences in drug response. Altered sensitivity to and clearance of propranolol in men of Chinese descent as compared with American whites

To determine whether the pharmacokinetics and pharmacodynamics of beta-blockade differ among racial groups, we gave 10 men of Chinese descent and 10 American white men 10, 20, 40, and 80 mg of propranolol every eight hours; the dosages were given in random order, and each dose was given for one day. The degree of beta-blockade was measured as the reduction in the heart rate and blood pressure in the supine and upright positions and during treadmill exercise testing. The Chinese subjects had at least a twofold greater sensitivity to the beta-blocking effects of propranolol than the white subjects, as indicated by the mean (+/- SEM) plasma concentrations producing a 20 percent reduction in the heart rate in both the supine position (197 +/- 31 vs. 536 +/- 58 nmol per liter; P less than 0.05) and the upright position (131 +/- 27 vs. 343 +/- 39 nmol per liter; P less than 0.05) and after exercise testing (96 +/- 12 vs. 185 +/- 23 nmol per liter; P less than 0.05). In addition, the Chinese subjects had much greater sensitivity to the hypotensive effects of propranolol, as shown by the concentrations that reduced blood pressure by 10 percent in the supine position (73 +/- 5 vs. 748 +/- 7 nmol per liter; P less than 0.01) and in the upright position (89 +/- 5 vs. 401 +/- 6 nmol per liter; P less than 0.01). No difference in beta-receptor density or affinity of lymphocytes was found between the groups. The Chinese group had a 45 percent higher free fraction of propranolol in plasma, which may have contributed to the increased drug effect but cannot explain it entirely. This group metabolized propranolol more rapidly than the white group, which resulted in a 76 percent higher clearance of an oral dose (3740 +/- 737 vs. 2125 +/- 214 ml per minute; P less than 0.05) because of increased metabolism through multiple metabolic pathways. We conclude that Chinese men have greater sensitivity than white men to the effects of propranolol on heart rate and blood pressure. Decreased protein binding may be responsible in part, but most of the effect remains to be explained.

Cocaine-induced coronary artery disease: recognition and treatment

Recreational use of cocaine has reached epidemic proportions. Recent reports have linked cocaine use to various acute and chronic cardiovascular disorders. The pharmacology of cocaine is discussed in this article, and the experiences with cocaine-induced coronary artery disease reviewed.

Increased fat and skeletal muscle beta-adrenergic receptors but unaltered metabolic and hemodynamic sensitivity to epinephrine in vivo in experimental human thyrotoxicosis

Based largely on evidence of increased target tissue beta-adrenergic receptor densities and responsiveness in animal and, to a lesser extent, human tissues, it is often assumed that thyroid hormone excess results in increased sensitivity to catecholamines in vivo, thus explaining several clinical manifestations of thyrotoxicosis. To test the hypothesis that thyrotoxicosis results in increased target tissue beta-adrenergic receptor densities and correspondingly increased metabolic and hemodynamic sensitivity to epinephrine in vivo, we measured these in 10 normal humans before and after administration of triiodothyronine (100 micrograms daily) for 10 d. Thyrotoxicosis increased beta-adrenergic receptor densities in fat (approximately 60%) and skeletal muscle (approximately 30%). Despite increments in beta-adrenergic receptor densities in these and probably other target tissues, metabolic and hemodynamic sensitivity to epinephrine in vivo was unaltered. An apparently adaptive increase in insulin secretion plausibly explains normal glycemic, glycogenolytic/glycolytic, lipolytic, and ketogenic sensitivity to epinephrine in the thyrotoxic state. In view of this striking homeostatic efficiency of the intact individual, the finding of altered adrenergic receptors, even in relevant target tissues, should not be extrapolated to altered sensitivity to catecholamines in vivo in the absence of direct testing of that hypothesis. With respect to the clinical issue, these data suggest that increased sensitivity to catecholamines does not explain clinical manifestations of thyrotoxicosis in humans.

Increased beta-receptor density and improved hemodynamic response to catecholamine stimulation during long-term metoprolol therapy in heart failure from dilated cardiomyopathy

Severe heart failure is associated with a reduction in myocardial beta-adrenergic receptor density and an impaired contractile response to catecholamine stimulation. Metoprolol was administered during a 6-month period to 14 patients with dilated cardiomyopathy to examine its effects on these abnormalities. The mean daily dose of metoprolol for the group was 105 mg (range, 75-150 mg). Myocardial beta-receptor density, resting hemodynamic output, and peak left ventricular dP/dt response to dobutamine infusions were compared in 9, 14, and 7 patients, respectively, before and after 6 months of metoprolol therapy while the patients were on therapy. The second hemodynamic study was performed 1-2 hours after the morning dose of metoprolol had been given. Myocardial beta-receptor density increased from 39 +/- 7 to 80 +/- 12 fmol/mg (p less than 0.05). Resting hemodynamic output showed a rise in stroke work index from 27 +/- 4 to 43 +/- 3 g/m/m2, p less than 0.05, and ejection fraction rose from 0.26 +/- 0.03 to 0.39 +/- 0.03 after 6 months of metoprolol therapy, p less than 0.05. Before metoprolol therapy, dobutamine caused a 21 +/- 4% increase in peak positive left ventricular dP/dt; during metoprolol therapy, the same dobutamine infusion rate increased peak positive dP/dt by 74 +/- 18% (p less than 0.05). Thus, long-term metoprolol therapy is associated with an increase in myocardial beta-receptor density, significant improvement in resting hemodynamic output, and improved contractile response to catecholamine stimulation. These changes indicate a restoration of beta-adrenergic sensitivity associated with metoprolol therapy, possibly related to the observed up-regulation of beta-adrenergic receptors.

Cyclic-AMP production by polymorphonuclear leukocytes in psychiatric disorders

The cyclic adenosine monophosphate (cAMP) responses to histamine, prostaglandin-E1, and isoproterenol in polymorphonuclear leukocytes from drug-free normal controls and patients with schizophrenia or major depressive disorder were compared. These three groups of subjects did not differ in their cAMP responses to receptor activation. Exacerbated and remitted patients with either schizophrenia or major depressive disorder did not differ in their cAMP responses. The data indicate that in polymorphonuclear leukocytes, the cAMP responses to activation of histamine H2, prostaglandin-E1, or beta-adrenergic receptors are neither state-independent nor state-dependent markers for schizophrenia or major depressive disorder.

Biphasic pattern of hypersensitivity following acute propranolol withdrawal in normal subjects

The effect of abrupt propranolol withdrawal on exercise-induced changes in heart rate and blood pressure was studied in six normal volunteers. Response to exercise was measured on two occassions during propranolol treatment and 1, 2, 3, 4, 5 and 7 days after the last dose of propranolol. Exercise-induced changes in heart rate were significantly lower than control during propranolol treatment (p less than 0.005). Following propranolol cessation, all subjects showed a biphasic pattern of hypersensitivity. Heart rate response was significantly greater than control 2, 3 and 7 days after the last propranolol dose (p less than 0.05) and not significantly different from control 1, 4 and 5 days after the last dose of propranolol. Exercise-induced changes in pulse pressure showed a biphasic pattern similar to the changes in heart rate.

Decreased cyclic AMP accumulation in lymphocytes in response to adrenaline and prostacyclin after n-3 polyunsaturated fatty acid supplementation in man

The effect of supplementation with n-3 polyunsaturated fatty acids on beta-adrenoceptor function in lymphocytes has been studied in ten healthy male volunteers. Ten Max-Epa capsules containing 320 mg n-3 polyunsaturated fatty acids per capsule were given for 3 weeks, and the cyclic AMP accumulation response in lymphocytes to adrenaline and the prostacyclin analogue iloprost (ZK 36374) were assessed before and after supplementation. After supplementation about 30% less cAMP was accumulation by the lymphocytes in response to either adrenaline or iloprost. Propranolol inhibited the adrenaline-induced increase in cAMP both before and after supplementation, but the difference in the basal cAMP concentration between the groups still persisted. Adrenaline stimulation after pre-incubation of the lymphocytes with the alpha-adrenoceptor antagonist phentolamine resulted in an even more pronounced difference between pre- and post-supplementation cAMP concentrations. The results suggest that fish oil supplementation may lead to decreased responsiveness of adenylate cyclase to catecholamine and prostaglandin stimulation.

The leucocytosis of exercise. A review and model

Exercise is known to induce an immediate leucocytosis, the magnitude of which is related, in most instances, to the intensity and duration of the work. On finishing exercise, however, the leucocyte count may change in any one of several different ways. The pattern of postexercise changes in the leucocyte count is determined mainly by the time which has elapsed since beginning exercise, rather than the work intensity or the total work done, if, for example, exercise has been intermittent. Consideration of, firstly, the circumstances under which the plasma concentrations of catecholamines and cortisol have been found separately to correlate with the leucocyte count at the finish of exercise, and, secondly, the effects on the leucocyte count of exogenous administration of these substances has led us to develop a model which can satisfactorily account for all of the principal changes in the leucocyte count that have been noted during and after exercise. It is proposed that catecholamines produced during exercise act to increase the ratio of circulating to non-circulating leucocytes, while cortisol acts, by a mechanism which involves a time lag, to increase the total number of leucocytes in the vascular compartment. Examination of previously published reports shows that many contain results which support this model. Using the model as a basis, some predictions are made that can be tested experimentally, and some experiments are suggested which should help elucidate the mode of action of catecholamines and cortisol.

Decreased beta-adrenergic receptor density and catecholamine response in male cigarette smokers. A study of monozygotic twin pairs discordant for smoking

The effect of long-term cigarette smoking on beta-adrenoceptor density and catecholamine response was studied in 10 monozygotic male twin-pairs discordant for smoking, with an average discordance time for smoking of 23 years (range, 12-35 years). The density of beta-adrenergic receptors was 40% lower in the lymphocytes of smoking twins compared with their nonsmoking cotwins (beta-receptor density, 6.7 +/- 1.2 and 11.1 +/- 1.8 fmol/10(6) cells, respectively; p less than 0.05). The corresponding apparent Kd values were 31.7 +/- 5.5 and 26.7 +/- 5.4 pM, respectively. Stimulation of the lymphocyte beta-receptors resulted in significantly lower levels of cyclic adenosine monophosphate in the smokers compared with the nonsmokers (16.2 +/- 3.3 vs. 29.2 +/- 6.5 pmol/10(6) cells, p less than 0.05). When subjected to submaximal exercise, the smokers had a lower level of cyclic adenosine monophosphate in plasma (25.9 +/- 1.2 vs. 28.6 +/- 1.0, p less than 0.05) and a net decrease was seen in plasma free fatty acids in the smokers compared with a net increase in the nonsmokers (-15% vs. +19%, p less than 0.01). The total plasma catecholamine level was, in the basal state, significantly higher in smokers compared with nonsmokers (74.8%, p less than 0.05). The intrapair difference in plasma norepinephrine predicted well the intrapair difference in beta-receptor density (r = -0.84, p less than 0.001). We conclude that the autonomic neurohumoral response evoked by cigarette smoking results in downregulation of beta-adrenergic receptors in long-term smokers.

Platelet function in classic migraine during attack-free periods

It has been reported that migraine sufferers have an enhanced platelet activity, as well as an enhanced thromboembolic risk. In this study, 12 subjects with classic migraine were compared with 12 age- and sex-matched controls. The following parameters were tested: platelet aggregation; platelet content of ADP, ATP and cyclic-AMP (cAMP); plasma levels of cAMP, 6-keto-PGF1 alpha and thromboxane B2, serum levels of TxB2 and lipids. ADP- and adrenaline-induced platelet aggregation, platelet content of ADP, ATP and cAMP did not differ significantly between the groups. Platelets from migraine subjects, however, showed a decreased beta-adrenoceptor response to stimulation with isoprenaline when determined as platelet cAMP production in vitro. The prostacyclin metabolite 6-keto-PGF 1 alpha was significantly decreased in the migraine group. No difference were observed in TxB2. Plasma lipids were similar, except that the migraine cases had higher levels of LDL-cholesterol. These data do not confirm a general platelet malfunction in migraine patients, but suggest a decreased functional capacity of platelet beta-adrenoceptors and an altered metabolism of prostacyclin and LDL-cholesterol.

Direct relationship between mononuclear leukocyte and lung beta-adrenergic receptors and apparent reciprocal regulation of extravascular, but not intravascular, alpha- and beta-adrenergic receptors by the sympathochromaffin system in humans

To examine putative relationships between adrenergic receptors on accessible circulating cells and relatively inaccessible extravascular catecholamine target tissues, we measured mononuclear leukocyte (MNL) and lung beta-adrenergic receptors and platelet and lung alpha-adrenergic receptors in tissues obtained from 15 patients undergoing pulmonary resection. Plasma catecholamine concentrations were measured concurrently to explore potential regulatory relationships between the activity of the sympathochromaffin system and both intravascular and extravascular adrenergic receptors. MNL and lung membrane beta-adrenergic receptor densities were correlated highly (r = 0.845, P less than 0.001). Platelet alpha 2-adrenergic receptor and lung alpha 1-adrenergic receptor densities were not. Lung alpha 1-adrenergic receptor densities were positively related to plasma norepinephrine (r = 0.840, P less than 0.01) and epinephrine (r = 0.860, P less than 0.01) concentrations; in contrast, lung beta-adrenergic receptor densities were not positively related to plasma catecholamine concentrations (they tended to be inversely related to plasma norepinephrine and epinephrine [r = -0.698, P less than 0.05] levels). This apparent reciprocal regulation of alpha- and beta-adrenergic receptors by the sympathochromaffin system was only demonstrable with adrenergic receptor measurements in the extravascular catecholamine target tissue. Neither MNL beta-adrenergic receptor nor platelet alpha-adrenergic receptor densities were correlated with plasma catecholamine levels. Thus, although measurements of beta-adrenergic receptors on circulating mononuclear leukocytes can be used as indices of extravascular target tissue beta-adrenergic receptor densities (at least in lung and heart), it would appear that extravascular tissues should be used to study adrenergic receptor regulation by endogenous catecholamines in humans. These data provide further support for the concept of up regulation, as well as down regulation, of some adrenergic receptor populations during short-term activation of the sympathochromaffin system in humans.

Propranolol attenuates exercise-induced increment in human lymphocytic beta-adrenergic receptors

The effect of peroral propranolol administration on the level of lymphocytic beta-adrenergic receptors was studied in six healthy volunteers using an acute exercise test. When no drug was used, a 15-min ergometer exercise period induced a significant increase in the receptor density (from 42 +/- 5 to 117 +/- 14 fmol/mg protein; mean +/- SEM), followed by a return to the pre-exercise level after a 1-hr rest. During propranolol administration (40 mg, three times daily), the basal receptor level (49 +/- 4 fmol/mg protein) did not change but the exercise-induced increment of the receptor density was significantly inhibited (peak value 79 +/- 5 fmol/mg protein, p less than 0.05). This effect could not be explained by direct competition for receptor binding sites by propranolol nor by differences in the plasma adrenalin and noradrenaline concentrations during the two tests. The fact that propranolol interferes with the normal adaptation of the beta-adrenergic receptor level to acute exercise may explain some of the adverse effects of beta-blocking drugs on physical performance.

Cyclic AMP second-messenger signal amplification in depression

Beta-adrenergic-mediated cyclic AMP accumulation was reduced in lymphocytes obtained from depressed patients from that observed in an age- and sex-matched group of control subjects. Among the depressed patients, those not responding to treatment showed significantly lower pretreatment responses to isoproterenol compared with patients who exhibited significant clinical improvement during antidepressant treatment. Late-night (terminal) insomnia was significantly associated with the blunted response to beta-adrenergic stimulation. In depressed patients with the lowest isoproterenol response, the effect of forskolin (which acts distal to the receptor and directly stimulates the catalytic subunit) on cyclic AMP accumulation was also significantly decreased. This suggests that post-receptor modulations of signal amplification also play a role in the reduced response to beta-adrenergic stimulation in depression.

Lymphocyte beta-adrenergic receptor binding in panic disorder

Lymphocyte beta adrenergic receptor binding using [125I]CNP was determined in patients with panic disorder (N = 4) or agoraphobia with panic attacks (N = 17) and age- and sex-matched healthy subjects (N = 22). The patients showed a significantly lower number of beta-adrenergic receptor binding sites and a significantly higher affinity of binding than healthy subjects. A past or present history of major depression in the patients did not alter these findings. These results are consistent with a growing body of knowledge implicating noradrenergic dysfunction in the pathophysiology of panic anxiety.

Modification of the response to opioid and nonopioid drugs by chronic opioid antagonist treatment

Chronic exposure to opioid antagonists increases the analgesic actions of opioids such as morphine. In the present studies, morphine's analgesic potency was increased (supersensitivity) following an 8 day subcutaneous naltrexone implant in mice, but not following a 1 day implant. Supersensitivity was maximal 24hr following the 8 day implant and declined linearly and had returned to control levels by 120hr. Implantation of naltrexone pellets for 8 days was found to increase the relative analgesic potency of methadone by 120%, while the lethal potency of cocaine was slightly (19%), but significantly, decreased. In contrast, identical treatment did not alter the potency of the benzodiazepine alprazolam to induce ataxia.

Calcium dependence of beta-adrenoceptor mediated cyclic AMP accumulation in human lymphocytes

In intact human lymphocytes, cyclic AMP accumulation in response to isoproterenol was inhibited by 5 mM EDTA, by deletion of calcium ions from the medium and by 1 mM lanthanum chloride, but not by 1 microM verapamil or by 10 microM nifedipine. A23187 caused a modest increase in cyclic AMP content. Exposure of lymphocytes to 5 microM 1-isoproterenol desensitized the cells to subsequent beta-adrenergic stimulation, reducing cyclic AMP accumulation. With higher concentrations of 1-isoproterenol (50 microM), receptor density was reduced as well. None of the above agents attenuated losses in agonist-stimulated cyclic AMP accumulation induced by treatment with 5 microM isoproterenol for 90 min. These data suggest that calcium ions, both those present in the extracellular medium and those bound to the plasma membrane, are required for isoproterenol-stimulation of adenylate cyclase. In addition, it appears that neither the presence of extracellular calcium ions nor full activation of adenylate cyclase are required for desensitization.

Sulfoconjugated catecholamines: lack of beta-adrenoceptor binding and adenylate cyclase stimulation in human mononuclear leukocytes

The racemic 3-O-sulfates of epinephrine and norepinephrine as well as 4-O-sulfoconjugated dopamine were synthesized, highly purified and investigated with respect to their beta-adrenoceptor affinities and relative potencies in the receptor-coupled adenylate cyclase system in isolated human mononuclear leukocytes. The receptor affinities of all catecholamine sulfates were reduced at least 1,000-fold when compared to those of the free catecholamines. Furthermore, catecholamine sulfoconjugates did not produce intracellular cAMP signals. In contrast to the sulfated catecholamine metabolites, the 3-O-methylated catecholamines metanephrine and normetanephrine were found to behave as endogenous beta-adrenoceptor-competing agents with lower beta-receptor affinities than the corresponding free catecholamines. No beta-receptor agonist activity in the adenylate cyclase system was found with metanephrine and normetanephrine. Our data provide direct evidence that sulfoconjugation renders catecholamines inactive as beta-receptor ligands and must thus be regarded as a mechanism to control adrenergic action at the prereceptor level by a buffering of the concentration of free catecholamines. The physiological significance of a potential role of 3-O-methylated catecholamines as endogenous beta-receptor antagonists has to be further clarified.

Alpha 2- and beta-adrenergic receptor binding and action in gluteal adipocytes from patients with hypothyroidism and hyperthyroidism

The alpha 2- and beta-adrenergic receptor activities have been investigated in human adipocytes in relation to thyroid status. Adipocytes from 11 hypothyroid and 18 hyperthyroid were compared with 19 euthyroid (normal) subjects. The lipolytic and cAMP responses to isoproterenol and epinephrine were greatly enhanced in adipocytes from hyperthyroid subjects (P less than .01) and impaired in adipocytes from hypothyroid subjects (P less than .05). However, the antilipolytic effect of clonidine (alpha 2-agonist) and the effect of clonidine on cAMP were similar in all three groups. The alpha 2- and beta-receptor numbers were both slightly increased in hyperthyroidism, but the ratio between the alpha 2- and beta-receptors was unchanged in relation to normal subjects. On the other hand, the adrenergic binding to adipocyte membranes from hypothyroid subjects was reduced, and the beta-receptor binding was reduced even much more (50%) than the alpha 2-receptor binding (20%, P less than .01). Thus, the alpha 2- and beta-receptor ratio was almost doubled in hypothyroid adipocytes (P less than .01). The antagonist affinity against the adrenergic receptors (determined by propranolol and yohimbine, respectively) was unchanged in the three groups. Agonist binding determined in intact adipocytes revealed unaltered affinity of clonidine for the alpha 2-receptor in the three groups. In hyperthyroidism, though, there was enhanced affinity of isoproterenol in competition with the beta-receptor (P less than .05). It is concluded that the inhibitory alpha 2-receptor pathway functions normally in all groups, indicating that the alpha 2-receptors and the alpha 2-receptor-mediated pathway in human adipocytes are relatively unaffected by thyroid hormones.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of propranolol on exercise induced tachycardia is determined by plasma concentration and the density of adrenergic receptors on leukocytes

The chronotropic response to a single oral dose of propranolol in 23 healthy subjects has been related to the plasma propranolol concentration and the density of beta-adrenoceptors on peripheral polymorphonuclear leucocytes. The percentage reduction in exercise-induced tachycardia was significantly correlated with the log plasma propranolol concentration within subjects but not between subjects. Taking the concentration of the active metabolite 4-hydroxypropranolol into account did not improve the interindividual correlation. The reduction in exercise-induced tachycardia was significantly correlated with the maximum binding density of (125I)-hydroxybenzylpindolol on polymorphonuclear leucocyte membrane fragments measured before medication. A response index (% reduction in exercise-induced tachycardia/plasma propranolol concentration) was correlated with the maximum binding density of (125I)-hydroxybenzylpindolol (pre-drug) at 2 h (rs = 0.72), 4 h (rs = 0.84) and 6 h (rs = 0.73) after dosing. The data suggest that interindividual variation in the response to propranolol after a single oral dose is determined by interindividual differences both in plasma propranolol and adrenoceptor density.

Inhibition of (-) [125I]-iodocyanopindolol binding to rat lung beta adrenoceptors by uremic plasma ultrafiltrates

Numerous data have suggested that beta-adrenoceptor-mediated responses were decreased in uremia and that parathormone could be implicated in this phenomenon. In a previous paper we have shown that the beta2 receptor density of mononuclear cells of uremic patients is significantly increased despite a significant increase in plasma epinephrine, suggesting that an endogenous substance could interfere and disregulate the beta 2 receptor density. In order to further evaluate this phenomenon we have firstly studied the influence of one non uremic and five uremic plasma ultrafiltrates on the binding of (-)-[125I]iodocyanopindolol using rat lung beta adrenoceptors. The results show that uremic plasma ultrafiltrates induce a decrease in the Bmax value without any variation on the Kd value. In a second step we have assessed the ability of human synthetic 1-34 and 53-84 parathormone to interact directly with beta-adrenoceptors. No variation in the (-)-[125I]iodocyanopindolol binding parameters was observed. These results suggest that an uremic endogenous substance might interfere on the beta adrenergic receptors and that the alteration in the beta-adrenergic response in uremia is probably not due to a direct action of parathormone on the beta-adrenoceptors.

Cardiovascular beta-adrenoceptor sensitivity of undernourished subjects

1. Eleven normal-weight male subjects (weight/height2 (W/H2) 19.0-22.5) from a good socio-economic background and on ad lib. food intake, and eight undernourished male labourers (W/H2 16.4-18.6) on low energy intakes, were studied. 2. Comparison of cardiovascular responses to increasing single doses of the beta-agonist, isoproterenol, showed a significantly greater positive chronotropic dose response in the undernourished subjects. 3. Cardiovascular responses to head-up tilt were similar in both the normal-weight and undernourished subjects. 4. Undernourished individuals may show an increase in beta-adrenoceptor sensitivity which may be akin to a denervation type of supersensitivity as a result of a nutrition-related reduction in sympathetic activity.

Adrenal catecholamine metabolism and myocardial adrenergic receptors in streptozotocin diabetic rats

Adrenal medullary function and myocardial adrenergic receptors were investigated in streptozotocin-treated diabetic rats. The animals were rendered diabetic by a single i.v. injection of streptozotocin (STZ, 65 mg/kg) and killed 60 days after treatment. Adrenal tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase (PNMT) activities were increased by 52, 28 and 39%, respectively, in the STZ diabetic rats. In addition, adrenal concentrations of dopamine (+52%) norepinephrine (+46%), and epinephrine (+33%) were elevated significantly (P less than 0.05). Increased adrenal TH activity reflected an increased Vmax, but no change in Km. Receptor densities (Bmax), determined by [3H]prazosin and [3H]dihydroalprenolol binding, were decreased by 24 and 25%, respectively, in the myocardium of 60-day diabetic rats. Insulin-induced chronic hypoglycemia in the STZ diabetic rats produced a marked increase in the adrenal TH concentration (Vmax, +65% or +225%, respectively), as compared to control or diabetic rats, without changes in the affinity (Km) for the substrate. These results suggest that the STZ diabetic rat has abnormalities of catecholaminergic function of the adrenal medulla and myocardial adrenergic receptors, which may contribute to the development and maintenance of many of the hemodynamic and metabolic defects described in this animal model of diabetes mellitus.

Chronic salt loading and adrenergic mechanisms in the Sprague-Dawley rat

The effect of chronic salt loading on adrenergic mechanisms was evaluated in Sprague-Dawley rats (and NMRI mice) maintained on a high sodium (8%) or normal sodium (0.3%) regime for 4 weeks. The basal blood pressure (carotid artery) was not influenced by the high salt diet but the heart rate and blood pressure increases to mental stress (jet air) were larger in the salt loaded rats. There were indications of an increased sympathetic tone in rats on the high salt diet since in these rats sympathoinhibitory treatment with ganglionic blockade or clonidine induced larger falls in blood pressure and heart rate than in the controls. Central catecholamines (brain stem, striatum, hemispheres) were determined spectrofluorimetrically after cation exchange chromatography. The high salt diet influenced neither the endogenous levels of noradrenaline nor central noradrenaline turnover (disappearance of noradrenaline after synthesis inhibition by alpha-methyltyrosine and accumulation of dihydroxyphenylalanine after decarboxylase inhibition by 3-hydroxybenzylhydrazine). There were no changes in central alpha 2-adrenoceptor responsiveness when assessed as clonidine-induced deceleration of noradrenaline turnover in the brain and in central alpha 1-adrenoceptor responsiveness (clonidine-induced increase of flexor reflex in spinalized rats and clonidine-induced increase of motor activity in reserpinized mice). Peripheral sympathetic function was assessed in pithed rats. The pressor responses to intravenously administered noradrenaline (0.01-10 micrograms/kg) and electrical stimulation of the spinal sympathetic nerves (SNS, 0.25-2 Hz) were similar in the two groups, suggesting that salt did not influence vascular alpha-adrenoceptor responsiveness or transmitter release.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of endogenous noradrenaline in the beta-blocker withdrawal phenomenon--studies with cultured heart cells

An in vitro model to evaluate the role of endogenous noradrenaline in the beta-blocker withdrawal phenomenon is described: Beating chicken heart muscle cells (5000 beta 1-adrenoceptors/cell) and heart nonmuscle cells (3000 beta 2-adrenoceptors/cell) were cultured in serum-free, hormone-supplemented medium. Basal state, subtype selective down-regulation of beta-adrenoceptors by endogenous noradrenaline (decrease in receptor number, beta 1 more than beta 2) was simulated by addition of noradrenaline to the culture medium; chronic beta-blockade was simulated by exposure of the cells for 3 days to various beta-blockers (propranolol, no ISA; timolol, slight ISA; pindolol, strong ISA). Beta-blocker withdrawal phenomenon--increased response in isoproterenol-induced cAMP production and positive inotropy--is correlated with the increase in the number of beta-adrenoceptors after withdrawal of the drugs. Propranolol induces a withdrawal phenomenon at every degree of noradrenaline-induced basal state down-regulation of beta-adrenoceptors; in contrast, a withdrawal phenomenon by pindolol is only seen at a higher degree of beta-adrenoceptor down-regulation. In the presence of physiological noradrenaline concentrations pindolol affects beta-adrenoceptor subtypes in a qualitatively different manner: the number of beta 1-adrenoceptors is increased, the number of beta 2-adrenoceptors is decreased. This finding demonstrates that the intrinsic sympathomimetic activity of nonselective beta-blockers can manifest itself only if the receptors are not strongly down-regulated. As beta 2-adrenoceptors are present in a much less down-regulated state than beta 1, ISA mainly acts on beta 2-adrenoceptor subtype, thus, presenting a beta 2-"pseudo-selectivity" of ISA.

The effect of chronic captopril therapy on adrenergic receptors, plasma noradrenaline and the vascular responses to infused noradrenaline

Adrenergic receptors (alpha 2, beta 2), plasma noradrenaline, heart rate and the pressor responsiveness to infused noradrenaline were examined in ten healthy male volunteers before and after 2 weeks of placebo or captopril therapy in a double blind cross-over study. No significant differences in these measurements were observed between the captopril and placebo treated groups. The study shows that in sodium replete normotensive subjects, long-term angiotensin converting enzyme inhibition does not lead to changes in adrenoceptor density. There is also no alteration in plasma noradrenaline levels nor in the pressor responsiveness to infused noradrenaline. These data suggest that the known interaction between the renin-angiotensin system and the sympathetic nervous system observed in animals is probably of little significance in man.