In vitro desensitization of beta adrenergic receptors in human neutrophils. Attenuation by corticosteroids.

The receptor alterations involved in catecholamine-induced desensitization of adenylate cyclase in human neutrophils have been investigated as has the ability of hydrocortisone to modify such alterations. Incubation of human neutrophils with isoproterenol for 3 h in vitro resulted in an 86% reduction in the ability of isoproterenol to stimulate cyclic AMP accumulation in the cells. Two types of receptor alterations were documented. There was a 40% reduction in the number of beta adrenergic receptors (42 vs. 25 fmol/mg protein, P < 0.005) present after desensitization as assessed by [(3)H]dihydroalprenolol ([(3)H]DHA) binding. In addition the receptors appeared to be relatively uncoupled from adenylate cyclase. This uncoupling was assessed by examining the ability of the agonist isoproterenol to stabilize a high-affinity form of the receptor, detected by computer modelling of competition curves for [(3)H]DHA binding. Desensitized receptors were characterized by rightward-shifted agonist competition curves. When hydrocortisone was added to the desensitizing incubations (combined treatment) there was a statistically significant attenuation in the desensitization process as assessed by the ability of isoproterenol to increase cyclic AMP levels in the cells. Although combined treatment did not prevent the decline in receptor number, it did attenuate the uncoupling of the receptors. Combined treatment resulted in competition curves intermediate between the control and the rightward-shifted desensitization curves. Prednisolone was similar to hydrocortisone in attenuating isoproterenol-induced uncoupling. Thus, steroids appeared to attenuate agonist-induced desensitization of the beta adrenergic receptor-adenylate cyclase system by dampening the ability of agonists to uncouple receptors without modifying their ability to promote down-regulation of beta adrenergic receptors.

Impaired formation of beta-adrenergic receptor-nucleotide regulatory protein complexes in pseudohypoparathyroidism.

Decreased activity of the guanine nucleotide regulatory protein (N) of the adenylate cyclase system is present in cell membranes of some patients with pseudohypoparathyrodism (PHP-Ia) whereas others have normal activity of N (PHP-Ib). Low N activity in PHP-Ia results in a decrease in hormone (H)-stimulatable adenylate cyclase in various tissues, which might be due to decreased ability to form an agonist-specific high affinity complex composed of H, receptor (R), and N. To test this hypothesis, we compared beta-adrenergic agonist-specific binding properties in erythrocyte membranes from five patients with PHP-Ia (N = 45% of control), five patients with PHP-Ib (N = 97%), and five control subjects. Competition curves that were generated by increasing concentrations of the beta-agonist isoproterenol competing with [125I]pindolol were shallow (slope factors less than 1) and were computer fit to a two-state model with corresponding high and low affinity for the agonist. The agonist competition curves from the PHP-Ia patients were shifted significantly (P less than 0.02) to the right as a result of a significant (P less than 0.01) decrease in the percent of beta-adrenergic receptors in the high affinity state from 64 +/- 22% in PHP-Ib and 56 +/- 5% in controls to 10 +/- 8% in PHP-Ia. The agonist competition curves were computer fit to a "ternary complex" model for the two-step reaction: H + R + N in equilibrium HR + N in equilibrium HRN. The modeling was consistent with a 60% decrease in the functional concentration of N, and was in good agreement with the biochemically determined decrease in erythrocyte N protein activity. These in vitro findings in erythrocytes taken together with the recent observations that in vivo isoproterenol-stimulated adenylate cyclase activity is decreased in patients with PHP (Carlson, H. E., and A. S. Brickman, 1983, J. Clin. Endocrinol. Metab. 56:1323-1326) are consistent with the notion that N is a bifunctional protein interacting with both R and the adenylate cyclase. It may be that in patients with PHP-Ia a single molecular and genetic defect accounts for both decreased HRN formation and decreased adenylate cyclase activity, whereas in PHP-Ib the biochemical lesion(s) appear not to affect HRN complex formation.

Evaluation of a rapid test kit for detection of HBsAg/eAg in whole blood: a possible method for pre-donation testing.

In many developing countries where hepatitis B is endemic, positivity rate for HBsAg in donor blood is high, and in some places, up to 20% of donated blood has to be discarded for being HBsAg positive. This degree of wastage may be financially crippling for some developing countries. Pre-donation testing may be useful, so that donors who test HBsAg positive are deferred and wastage of costly blood bags is reduced. The study is to evaluate the suitability of the AMRAD kit, for pre-donation testing for HBsAg. One hundred and one (101) healthy blood donors were screened for HBsAg/eAg using the test kit. The same specimens were screened using Monolisa (ELISA) kits for HBsAg and eAg as the standard. True positive (TrP), False negative (FN), True negative (TrN) and, false positive (FP) values were then found, from which, sensitivity and specificity, were derived. The AMRAD test kit detected 93 specimens as negative and 8 specimens as positive for HBsAg as against 94 negatives (TrN) and 7 positives (TrP) by monolisa. Thus, one false positive (FP) result was found in using the kit while no false negative (FN) occurred. The findings in this preliminary study suggest that AMRAD kit may be a useful predonation screening test for HBsAg.

Lymphocyte beta-adrenergic receptor modification in bulimia.

beta-Adrenergic receptor binding on circulating lymphocytes was evaluated in young female bulimic patients (n = 12) and age- and sex-matched normal control volunteers (n = 10). Using iodine 125-labeled cyanopindolol, antagonist binding was evaluated (number of receptors [Bmax] and dissociation constant [KD]), and using isoproterenol competition of cyanopindolol binding, the concentration required to inhibit binding by 50% (IC50) for isoproterenol and the agonist affinity measure of KL/KH (ratio of dissociation constants for the low- and high-affinity states of the receptor) were determined. Plasma norepinephrine (NE) level was also measured. There was a trend toward lower plasma NE levels in the bulimic patients. The KL/KH ratio in bulimic patients was significantly greater than that for the normal volunteers, indicating increased receptor coupling. The KL/KH ratio was not significantly correlated with plasma NE level. Neither Bmax nor KD was different between the two groups. These findings suggest that beta-adrenergic receptors in bulimic patients may be more responsive than in normal subjects, without alteration of the traditional measures of receptor responses, a difference that cannot be explained on the basis of plasma NE. These findings provide another line of evidence for altered regulation of the noradrenergic system in bulimic patients during a controlled phase of their illness.

Polymorphonuclear leukocyte function in psoriasis: chemotaxis, chemokinesis, beta-adrenergic receptors, and proteolytic enzymes of polymorphonuclear leukocytes in the peripheral blood from psoriatic patients.

Psoriatic patients, particularly those with psoriatic arthritis, have neutrophilic and eosinophilic leukocytosis. Isolated polymorphonuclear leukocytes (PMNLs) from psoriatic patients have normal concentrations of proteolytic enzymes and they have beta-adrenergic receptors of normal density and affinity. PMNLs from psoriatic patients responded normally to the synthetic chemotactic peptide, f-Met-Leu-Phe (formyl-methionine-leucine-phenylalanine). The chemotactic activities of sera from psoriatic patients were similar to those of normal sera. Sera from psoriatic patients enhanced chemokinesis of PMNLs more than normal control sera at a final concentration of 1%; no difference in chemokinetic response between psoriatic and normal sera was found at serum concentrations greater than 2.5%. This study suggests that the peripheral PMNLs from psoriatic patients are normal, but the sera of psoriatic patients has more chemokinetic activity for PMNLs than does normal serum.

Myocardial beta-adrenergic receptors from adrenalectomized rats: impaired formation of high-affinity agonist-receptor complexes.

Adrenal steroid hormones potentiate beta-adrenergic actions on the heart. Accordingly, we investigated the effects of adrenalectomy on agonist and antagonist interactions with myocardial beta-adrenergic receptors and adenylate cyclase. The affinity and number of beta-adrenergic receptor sites, both defined by the antagonist (-) [3H]dihydroalprenolol, did not change after adrenalectomy. Computer modelling of agonist (-)-isoproterenol competition curves indicated the presence of two discrete receptor states with high and low affinities. After adrenalectomy, the agonist curves were shifted to the right, and the dissociation constant of the high-affinity state significantly rose from 12 to 48 nM (p < .001), but the dissociation constant of the low affinity state was unchanged. Although basal, maximal isoproterenol-stimulated and fluoride-stimulated adenylate cyclase activities were unaltered, the EC50 for isoproterenol stimulation was increased significantly from 490 to 1500 nM (p <.018). These results suggest that adrenal steroid hormones may regulate the ability of the beta-adrenergic receptors to form a high-affinity "coupled" state, presumably by modulating the interaction of the receptor with nucleotide regulatory proteins.

Rapid desensitization and uncoupling of human beta-adrenergic receptors in an in vitro model of lactic acidosis.

Adrenergic responsiveness in many tissues may be impaired in the presence of lactic acidosis. The purpose of this study was to examine how human neutrophil beta 2-adrenergic receptors may be altered in an in vitro model of lactic acidosis. Receptor coupling was assessed by constructing curves for the competition of isoproterenol with [125I]iodocyanopindolol for beta-adrenergic receptors. Receptors were exposed to control (2 mM lactate, pH 7.4), lactic acidosis (16 mM lactate, pH 7.1), lactate excess (16 mM lactate, pH 7.4), and low pH (2 mM lactate, pH 7.1) conditions. Prior exposure of beta-adrenergic receptors on whole cells to lactic acidosis resulted in a 61% reduction in isoproterenol-stimulated cAMP accumulation (P less than 0.005). This desensitization was not accompanied by down-regulation. After exposure to lactic acidosis, beta-adrenergic receptors were uncoupled sufficiently that a high affinity state could not be detected. Both lactate excess and low pH were necessary to fully express the desensitization and uncoupling defects. The uncoupling was rapid (40 min) and occurred in cell-free membrane preparations. Thus, in an in vitro model of lactic acidosis, rapid desensitization and uncoupling occur which do not appear to require protein synthesis.

Corticosteroid-induced differential regulation of beta-adrenergic receptors in circulating human polymorphonuclear leukocytes and mononuclear leukocytes.

A method of reproducibility measuring human leukocyte beta-adrenergic receptor density and affinity has been developed and applied to the study of receptor regulation in man. The method has the advantages of using a membrane preparation which binds highly specifically and employing techniques such as using low concentrations of [3H]dihydroalprenol, analyzing the data by computer modelling techniques, and providing data from both granulocytes and lymphocytes in the same individual to minimize measurement errors. Using this methodology, human beta-adrenergic receptor regulation is examined. Cortisone acetate was found to induce an acute rise in granulocyte beta-adrenergic receptor density and adenylate cyclase activity and an acute fall in lymphocyte beta-adrenergic receptor density. This potentially differential regulation of a single receptor subtype in two lines of leukocytes has important implications for the study of receptor regulation in man using leukocyte models.

Agonist-promoted high affinity state of the beta-adrenergic receptor in human neutrophils: modulation by corticosteroids.

beta-Adrenergic agonists form high affinity complexes with receptors, resulting in activation of the associated adenylate cyclase. To examine the formation of the high affinity state of the receptor, curves were constructed for the competition of the full beta-adrenergic agonist isoproterenol, partial agonists cobefrin and soterenol, and the antagonist propranolol for [3H]dihydroalprenolol binding to beta-adrenergic receptors on human neutrophil membranes. Curve modeling by computer yielded a two-state binding model for the agonists, with distinct dissociation constants for the high (KH) and low (KL) affinity states. The ratio of dissociation constants (KL/KH) was found to be well correlated (P less than 0.01) with the drug's intrinsic activity for stimulation of adenylate cyclase. Thus, the degree of coupling of receptor occupation with adenylate cyclase activation is correlated with the magnitude of KL/KH. Administration of cortisone to humans resulted in a substantial rise in the proportion of receptors in the high affinity state and in the KL/KH determined from isoproterenol competition curves, as well as a rise in adenylate cyclase activity. Furthermore, in vitro exposure of human neutrophils to hydrocortisone resulted in a similar rise in KL/KH determined from isoproterenol competition curves. Therefore, one mechanism by which cortisone modulates beta-adrenergic receptor function appears to be through facilitating the formation of the high affinity state of the receptor, resulting in greater coupling of receptor occupation with adenylate cyclase activation.

Abnormal guanine nucleotide regulatory protein in MVP dysautonomia: evidence from reconstitution of Gs.

We and others have used the term MVP dysautonomia for a particular subset of hyperadrenergic dysautonomia patients. The role of the stimulatory guanine nucleotide regulatory protein (Gs) in this dysautonomia was studied by cholate extraction of Gs from erythrocytes from 11 normal subjects and 14 symptomatic dysautonomic patients and reconstitution into cyc-S49 lymphoma membranes, which have normal receptor and adenylyl cyclase but lack Gs. Isoproterenol-stimulated adenylyl cyclase activity in the dysautonomia group was increased compared to that in controls [3.66 +/- 0.20 (mean +/- SE; n = 14) vs. 2.87 +/- 0.14 (n = 11) U cyc- reconstituted activity/mg erythrocyte protein; P less than 0.05]. beta-Adrenergic receptor high affinity state formation was greatest in the severely symptomatic group [KL/KH: severe symptoms, 130 +/- 48 (n = 6); mild symptoms, 33 +/- 7 (n = 7); control, 27 +/- 6 (n = 11); severe dysautonomia distinct, P less than 0.017]. Sodium dodecyl sulfate-polyacrylamide gels of cholera toxin-dependent ADP-ribosylated G-proteins yielded no gross distinction between severely symptomatic and control groups. This subset of hyperadrenergic dysautonomia patients, thus, has supercoupled beta 2-adrenergic receptors (increase in both agonist binding and cyclase activation) conferred by an abnormal Gs, whose effects on agonist binding reflect the severity of illness.

Diversity in supercoupling of beta 2-adrenergic receptors in orthostatic hypotension.

Orthostatic hypotension is a clinical condition that frequently involves abnormal adrenergic control of cardiovascular function. Adrenergic function was studied in six patients with symptomatic orthostatic hypotension and in 11 age-matched healthy subjects. The patients demonstrated higher supine mean arterial pressures (MAP; 103 +/- 8 versus 86 +/- 4 mm Hg) and orthostatic hypotension (delta MAP -70 +/- 5 versus +15 +/- 2 mm Hg, p less than 0.001) compared with normal subjects. The delta MAP in phase II of the Valsalva maneuver was significantly greater (-31 +/- 4 versus -7 +/- 4 mm Hg, p less than 0.002) and phase IV heart rate response was blunted (-5 +/- 3 versus -30 +/- 8 beats/min, p less than 0.02) in these patients. More isoproterenol was required to increase heart rate by 25 beats per minute in patients with hypotension (810 +/- 670 versus 3.1 +/- 1.3 micrograms, p less than 0.05), indicating marked chronotropic hyposensitivity. Leukocyte beta 2-adrenergic receptor densities were similar in patients and controls. beta 2-Adrenergic receptor coupling, however, was elevated in patients with hypotension when compared with control subjects (ratio of the low-affinity and high-affinity dissociation constants [KL/KH] 140 +/- 7.4 versus 66 +/- 4.3, p less than 0.001). There were negative correlations between the KL/KH value and the dose of isoproterenol required to decrease MAP by 20 torr (p less than 0.02) and between the KL/KH value and the product of the hormone receptor and MAP (p less than 0.01). However, the patients could be subdivided into a group who could mount a nearly normal hormone receptor times MAP response on standing (group 1A), and a group who could not (group 1B). The group 1A patients had elevated plasma norepinephrine responses associated with milder beta 2-adrenergic receptor supercoupling, whereas group 1B patients had essentially no orthostatic plasma norepinephrine response and had much higher KL/KH values. Thus, though a state of biochemical supersensitivity existed in both patient subgroups, diminished catecholamine exposure was associated, as expected, with beta 2-adrenergic hypersensitivity in group 1B, whereas there was no diminution of catecholamine exposure in the beta 2-adrenergic hypersensitivity observed in group 1A patients.

Mitral valve prolapse with symptoms of beta-adrenergic hypersensitivity. Beta 2-adrenergic receptor supercoupling with desensitization on isoproterenol exposure.

Autonomic nervous system dysfunction has recently been identified in a subset of patients with mitral valve prolapse. These autonomic nervous system abnormalities may correspond, in part, to biochemical alterations in beta-adrenergic receptors. Nine women with mitral valve prolapse and symptoms and signs of beta-adrenergic hypersensitivity and seven normal volunteer women were studied. Quiet standing (five minutes) increased both heart rate and plasma norepinephrine (p less than 0.05) in symptomatic patients with mitral valve prolapse compared with normal subjects. The dose of isoproterenol required either to increase heart rate 25 beats/minute (0.5 +/- 0.3 microgram versus 1.0 +/- 0.3 microgram) or to decrease mean arterial pressure 20 mm Hg (11.1 +/- 4.8 versus 78.2 +/- 25.2 micrograms) was significantly less in the patients with mitral valve prolapse than in the volunteers. Symptomatic patients with mitral valve prolapse were desensitized by a four-hour isoproterenol infusion, whereas sensitivity in normal control subjects did not change. In the patients with mitral valve prolapse, baseline beta-adrenergic receptor coupling was elevated compared with that in control subjects (220 +/- 7 versus 81 +/- 2; p less than 0.001). Isoproterenol infusion induced uncoupling in these patients (KL/KH = 35 +/- 3, p less than 0.05) but did not alter coupling in normal volunteers. This study demonstrates physiologic and pharmacologic beta-adrenergic hypersensitivity in vivo directly corresponding to biochemical supercoupling in a subset of patients with mitral valve prolapse.

Spectrum of dysautonomia in mitral valvular prolapse.

PURPOSE: Symptoms suggesting altered autonomic regulation of cardiovascular function have been noted in some patients with mitral valvular prolapse (MVP) but may also occur in patients with other disorders. We evaluated cardiovascular responses to autonomic stimuli in 118 patients with symptoms of dysautonomia, 78 of whom had MVP, and 40 of whom did not, to determine if unique patterns of these responses distinguished patients in one symptomatic subgroup from another. SUBJECTS AND METHODS: The responses of patients to standing, quantitated Valsalva maneuver, facial immersion in ice water, and administration of isoproterenol, phenylephrine, and tyramine were compared with those in 12 asymptomatic patients with MVP and 23 normal volunteers. RESULTS: Constitutional, cardiovascular, and neuropsychiatric symptoms occurred with similar frequency in the two symptomatic patient groups. The most common pattern of abnormal responses in symptomatic patients with or without MVP was (1) an increased heart rate and elevated plasma norepinephrine levels while supine and then while standing quietly for five minutes, (2) an exaggerated increase in heart rate during phase II of Valsalva, (3) a diminished bradycardic response during phase IV of Valsalva, and (4) an exaggerated heart rate response to administration of isoproterenol. The increased heart rate during Valsalva, but not the exaggerated sensitivity to isoproterenol, was correlated with the magnitude of the chronotropic response to standing only in symptomatic patients with MVP. Exaggerated hypertensive overshoot during phase IV of Valsalva was observed in only a few symptomatic patients. No consistent pattern of these abnormalities, however, was noted in any of the patient subgroups. Hemodynamic responses to autonomic stimuli in asymptomatic MVP patients were generally indistinguishable from those observed in normal subjects. CONCLUSION: These findings suggest that abnormal cardiovascular responses to autonomic stimuli may occur in any patient with symptoms of dysautonomia regardless of the presence or absence of MVP and that the pattern of these abnormal responses may be diverse. It is therefore important to characterize the pattern of altered autonomic regulation of cardiovascular function in each patient when considering mechanistic implications or making therapeutic decisions about these patients.

Exercise-induced fall in coupling of human beta 2-adrenergic receptors.

The purpose of this study was to quantitatively examine to what extent acute exertion diminishes the activity of beta-adrenergic receptors through diminishing coupling. Normal neutrophil membrane preparations containing beta 2-adrenergic receptors were obtained from healthy human volunteers, then exposed to autologous venous plasma obtained before and after acute forearm exertion. There was an acute, dramatic diminution in coupling (P less than .003) after only a few minutes of exercise. Preexertion plasma had no significant effect upon coupling. Substantial diminution in beta-adrenergic receptor sensitivity is thus acutely demonstrable in this model which serves as a model for both metabolic acidosis and acute exertion.

Abnormal Gs function in mitral valve prolapse dysautonomia is not associated with abnormal alpha S cDNA sequence.

We have previously shown that a subset of patients with mitral valve prolapse and hyperadrenergic symptoms has enhanced isoprenaline-stimulated beta-adrenergic receptor high-affinity state formation (supercoupling) and increased adenylyl cyclase activity due to abnormal signal transduction by the stimulatory guanine nucleotide regulatory protein (Gs). In this study we looked for an alteration of the nucleotide coding sequence of the gene for alpha s, the subunit of Gs that is directly responsible for formation of the high affinity state and adenylyl cyclase activation, by cloning and sequencing the alpha s cDNA from neutrophils of 4 symptomatic patients and 1 control. No difference was observed between patients and control in the alpha s cDNA sequence. The splice variant concentrations in the fully expressed protein were also grossly unchanged in five patients and four controls. These data show that a primary alteration of the alpha s gene coding sequence is not responsible for defective Gs-associated signal transduction in dysautonomic MVP patients, and suggest that the molecular lesion could be an abnormal posttranslational modification of alpha s, a defect in the beta or gamma subunits of Gs, or an unusual interaction between the subunits in the Gs of these patients.

Effects of endogenous redox-active compounds on coupling of human beta 2-adrenergic receptors.

Altered redox states such as metabolic acidosis may impair beta-adrenergic receptor responsiveness. Beta-adrenergic receptor function requires formation of a high affinity, "coupled" state of the receptor. The degree of coupling is reflected in the ratio of dissociation constants, KL/KH, for the low and high affinity states of the receptor. It has previously been demonstrated that 16 mM lactate and pH 7.1 induce independent defects in beta-adrenergic receptor function. The purpose of this study was to examine further how endogenous redox agents might alter high affinity state formation. Normal neutrophil membrane preparations containing beta-adrenergic receptors were exposed to several concentrations of three redox couplets native to plasma: lactate (L)-pyruvate (P), beta-hydroxybutyrate (BOHB)-acetoacetate (AcAc), and glutathione (GSH-GSSG). BOHB, AcAc, and P had no isolated effect on high affinity state formation while 10 mM lactate diminished KL/KH by 30% (p less than 0.001). Dropping the pH from 7.4 to 7.1 resulted in a 50% to 70% reduction in KL/KH (p less than 0.001), independent of metabolite present. GSH or GSSG exposure resulted in a concentration-dependent fall in KL/KH value. Thus, high affinity state formation is regulated by redox couplets and pH independently. The reduced responsiveness of beta-adrenergic receptors observed in such states as metabolic acidosis could result from direct effects of redox couplets in addition to those of low pH.

Absolute lymphocyte count as surrogate for CD4+ cell count in monitoring response to antiretroviral therapy.

The objective of the study is to determine whether Absolute Lymphocyte Count (ALC) can serve as a surrogate for CD4 T-lymphocyte Cell Count (CCC) in HIV infected Nigerians on Lamivudine/Zidovudine anti-retroviral therapy. 32 adult Nigerians infected with HIV were recruited into the study. They were assessed clinically and categorised into three clinical stages A, B and C according to CDC criteria. They all received lamivudine 150 mg b.d and Zidovodine 300 mg b.d for six months. Blood specimens were taken on enrollment and at four weekly intervals for paired ALC and CCC determination. ANOVA statistics was used to determine whether ALC and CCC (separately) change significantly with increasing duration of therapy. Paired ALC and CCC values were tested for correlation. Sensitivity and specificity of low ALC values in predicting low CCC values were also calculated. The 32 patients comprised 18 males and 14 females aged between 16 and 49 years. The mean age (SD) was 36.1 (+/-7.85) years. The mean ALC value rose from 2485/l and 2352/microl before commencement of therapy to 3026/microl and 3151/microl four weeks after for males and females respectively. These changes were not significant, P>0.05. No further changes were noted over the next 24 weeks. However, the mean CCC values increased from 233/microl before therapy through 339/microl at four weeks, 362/microl at eight weeks to 398/micro1 at 12 weeks. It then fluctuated between 372/microl and 310/microl for the remaining part of the study. These changes were not significant: F: ratio = 1.28 (df = 6,181), P>0.05. A weak but significant positive correlation was established between ALC and CCC. Correlation coefficient was 0.25, P<0.05. The sensitivity and specificity of ALC 2000/microl as a predictor of CCC 200/microl were 57% and 72% respectively. ALC correlates weakly with CCC in patients undergoing antiretroviral therapy and it may not serve as a perfect surrogate for CCC as a monitor of immunological response to therapy.

Coupling of human beta 2-adrenergic receptors: relationship to redox potential.

The purpose of this study was to examine the quantitative relationship between the redox potential of a redox couplet and the alterations it induces in coupling of receptor occupation with enzyme activation. Normal neutrophil membrane preparations containing beta 2-adrenergic receptors were exposed to equimolar mixtures of the following redox couplets: ferrocyanide-ferricyanide, hemoglobin-methemoglobin, ascorbate-dehydroascorbate, lactate-pyruvate, glutathione ox-red, beta-hydroxybutyrate-acetoacetate, and NAD-NADH. There was a linear relationship between the redox potential of the couplets and the degree of change in coupling (p less than 0.001). The apparent redox potential of the high affinity complex was +0.30 +/- 0.093 V. The effect of lactate to uncouple beta-adrenergic receptors was partially blocked by preexposure to isoproterenol. Thus, high affinity state formation is regulated by redox couplets in a manner dependent on their redox potential.

Oral diazepam premedication reduces the incidence of post-succinylcholine muscle pains.

In a prospective, double-blind placebo controlled trial, the effect of oral diazepam premedication on post-succinylcholine fasciculations and myalgia was studied. Forty patients undergoing septoplasty procedures received orally identical capsules containing either 10 mg of diazepam or a placebo 90 minutes preoperatively. A standardized anaesthetic regimen included induction with 5 mg X kg-1 of thiopental and 1 mg X kg-1 of succinylcholine. The diazepam and control groups did not differ significantly in extent of fasciculations or ease of intubation. However, only 15 per cent of the diazepam premedicated patients had myalgias postoperatively compared to 50 per cent of the control patients, a statistically significant difference (p = 0.04).