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R D Feldman

Publications and source records attributed to R D Feldman.

At least 73 records · Page 4Linked to original sources
PubMed1989

Beta-adrenergic desensitization reduces the sensitivity of adenylate cyclase for magnesium in permeabilized lymphocytes.

Magnesium modulates hormone-sensitive adenylate cyclase activation. In the present studies, we have examined the magnesium requirement of beta-adrenergic-stimulated adenylate cyclase activity in permeabilized human lymphocytes. Following isoproterenol pretreatment, under conditions that lead to homologous beta-adrenergic desensitization, the EC50 of magnesium for beta-adrenergic-stimulated adenylate cyclase activity was significantly increased [control; 1.99 (+0.81/-0.57) mM; desensitized; 3.82 (+0.31/-0.29) mM]. Further, when assays were performed at high Mg2+ concentrations following agonist pretreatment, we detected only small and inconsistant reductions in beta-adrenergic-stimulated adenylate cyclase activity and in beta-adrenergic cAMP-dependent protein kinase activity. In contrast, the detection of agonist-induced beta-adrenergic receptor sequestration and alterations in receptor affinity for agonists was not qualitatively affected by changes in magnesium concentrations. The data demonstrate that the functional consequences of beta-adrenergic desensitization may be obscured at high magnesium concentrations. Furthermore, in this system desensitization may be viewed as a beta-receptor-specific reduction in magnesium sensitivity.

Adenylyl Cyclases↗
PubMed1987

Beta-adrenergic-receptor-mediated suppression of interleukin 2 receptors in human lymphocytes.

Adrenergic receptor agonists are known to attenuate the proliferative response of human lymphocytes after activation; however, their mechanism of action is unknown. Since expression of interleukin 2 (IL-2) receptors is a prerequisite for proliferation, the effect of beta-adrenergic receptor agonists on lymphocyte IL-2 receptors was studied on both mitogen-stimulated lymphocytes and IL-2-dependent T lymphocyte cell lines. In both cell types the beta-adrenergic receptor agonist isoproterenol blocked the expression of IL-2 receptors, as determined with the IL-2 receptor anti-TAC antibody. To determine the effect of beta-adrenergic agonists on expression of the high affinity IL-2 receptors, [125I]IL-2 binding studies were performed at concentrations selective for high affinity sites. No significant effect of beta-adrenergic agonists on high affinity IL-2 receptor sites could be detected. The data demonstrate that beta-adrenergic receptor agonists down-regulate IL-2 receptors primarily affecting low affinity sites.

Adrenergic beta-Agonists↗
PubMed1987

Clinical pharmacology and therapeutics education for senior medical students.

In many medical schools instruction of students in clinical pharmacology remains informal and may be inadequate. To determine the short-term efficacy of a mandatory senior medical year course in clinical pharmacology, we compared examination scores of senior students in the College of Medicine, University of Iowa, either prior to or following the Clinical Pharmacology and Therapeutics Lecture Series. A significantly higher (P less than .001) mean score was demonstrated by students taking the examination following the course (75 +/- 4% correct) versus those taking the examination prior to the course (55 +/- 4% correct). To determine student acceptance, postcourse questionnaires were completed. Students surveyed immediately postcourse and alumni surveyed up to four years after graduation highly recommended the course and favored retaining it as a mandatory part of the fourth-year curriculum. This study confirms the efficacy and acceptance of senior medical courses in therapeutics and suggests an effective role for clinical pharmacologists in their design and execution.

Curriculum↗
PubMed1987

Are lymphocyte beta-adrenoceptors altered in patients with cystic fibrosis?

1. Beta-adrenergic responsiveness may be decreased in cystic fibrosis. In order to determine whether this reflects an alteration in the human lymphocyte beta-receptor complex, we studied 12 subjects with cystic fibrosis (six were stable and ambulatory and six were decompensated, hospitalized) as compared with 12 normal controls. 2. Lymphocyte beta-receptor mediated adenylate cyclase activity (EC 4.6.1.1) was not decreased in the ambulatory cystic fibrosis patients as compared with controls. In contrast, decompensated hospitalized cystic fibrosis patients demonstrated a significant reduction in beta-receptor mediated lymphocyte adenylate cyclase activity expressed as the relative increase over basal levels stimulated by the beta-agonist isoprenaline compared with both normal controls and stable ambulatory cystic fibrosis patients (control 58 +/- 4%; ambulatory cystic fibrosis patients 51 +/- 7%; decompensated hospitalized cystic fibrosis patients 28 +/- 5%; P less than 0.05). 3. Our data suggest that defects in lymphocyte beta-receptor properties in cystic fibrosis patients may be better correlated with clinical status than with presence or absence of the disease state.

Adenylyl Cyclases↗
PubMed1987

Digoxin toxicity in patients with high serum digoxin concentrations.

A retrospective study of the clinical course and outcome of patients with serum digoxin concentrations (SDCs) greater than 3 ng/mL was conducted to determine the probability of a patient without initial signs or symptoms of digoxin toxicity subsequently developing signs or symptoms. Of 123 patients with SDCs greater than 3 ng/mL, 54 had no apparent signs or symptoms of toxicity at the time the index SDC was determined (group 1). Of these 54, two patients developed definite digoxin toxicity, although neither suffered significant morbidity. Digoxin administration was reduced or discontinued in all patients but one in group 1. There were no significant differences between the patients who had no signs or symptoms of digoxin toxicity (group 1) and those who did have signs or symptoms (group 2) in the mean SDC (3.9 +/- 0.1 vs 4.2 +/- 0.2 ng/mL, respectively), the serum creatinine (2.9 +/- 0.2 vs 3.4 +/- 0.4 mg/dL), or the incidence of atrial fibrillation (29/54 vs. 35/69) and coronary artery disease (21/54 vs. 18/69). The authors conclude that clinically stable patients receiving digoxin who have elevated SDCs but are without signs or symptoms of digoxin toxicity are at low risk of developing serious digoxin toxicity and do not generally require treatment beyond the discontinuation of digoxin therapy.

Aged↗
PubMed1987

Beta-adrenergic receptor alterations in hypertension--physiological and molecular correlates.

In hypertensive animals, there is physiological and biochemical evidence that beta-adrenergic responsiveness is diminished. In contrast, in man the physiological evidence of reduced beta-adrenergic responsiveness is not completely convincing and few biochemical studies have been reported. The lymphocyte has been widely used as a model for the human beta-adrenergic receptor complex. In studies comparing young normotensive and mild hypertensive subjects we demonstrated a reduction in beta-adrenergic mediated adenylate cyclase activity in lymphocytes from hypertensive subjects. A parallel reduction in beta-adrenergic receptor affinity for agonists was also seen. These changes are consistent with a functional uncoupling of the receptor from the adenylate cyclase complex. To determine the role of dietary sodium intake on beta-adrenergic receptor properties in hypertension we studied lymphocytes from hypertensive and normotensive subjects fed either a low (10 mequiv.) or high (400 mequiv.) NaCl diet. We demonstrated that a low NaCl diet corrected the defect in lymphocyte beta-adrenergic responsiveness in hypertension. These studies emphasize the utility of biochemical approaches to the study of alterations in beta-adrenergic responsiveness in human hypertension and suggest an important role of dietary sodium in the reduction in beta-adrenergic responsiveness in the hypertensive state.

Animals↗
PubMed1987

Low sodium diet corrects the defect in lymphocyte beta-adrenergic responsiveness in hypertensive subjects.

To determine the role of dietary sodium intake in the reduction in beta-adrenergic sensitivity in hypertension, lymphocyte beta-receptors from 8 borderline hypertensive and 16 normotensive subjects were studied after 5 d on a high sodium diet (400 meq/d) and also following a low sodium diet (10 meq/d). During the high sodium diet, lymphocyte beta-receptor-stimulated adenylate cyclase activity, expressed as the relative increase over basal levels stimulated by the beta-agonist isoproterenol, was significantly (P less than 0.025) decreased in hypertensive (24 +/- 5%, mean +/- SE) compared with normotensive (42 +/- 4%) subjects. Neither beta-receptor density nor the proportion of nonsequestered beta-receptors differed between groups. A low sodium diet significantly increased beta-receptor-stimulated adenylate cyclase activity in hypertensives (low sodium, 51 +/- 7%; high sodium, 24 +/- 5%, P less than 0.025) to a level not different than that of normotensives (46 +/- 5%). Thus, reduced lymphocyte beta-receptor responsiveness in hypertensive subjects is not due to beta-receptor sequestration and is corrected on a low sodium diet. Dietary sodium may be an important factor in the beta-receptor defect in early hypertension.

Adenylyl Cyclases↗
PubMed1986

Temperature-dependent binding of hydrophilic beta-adrenergic receptor ligands to intact human lymphocytes.

Important differences in binding characteristics between agonists and antagonists of the beta-adrenergic receptor have been described. However, these observations have been complicated since most available antagonists are much more lipophilic than agonists. In order to separate out those binding characteristics of agonist vs. antagonist from those characteristics of lipophilic vs. hydrophilic ligands, we have studied competition of the hydrophilic ligands isoproterenol (agonist) and CGP-12177 (antagonist) with [125I]iodopindolol binding in intact human lymphocytes. Analyzing competition curves from assays performed at 13 degrees C, 25 degrees C and 37 degrees C we demonstrated that at lower temperatures there was a decrease in IC50 for isoproterenol but not for CGP-12177. Using cells preincubated with isoproterenol then extensively washed, competition curves with both isoproterenol and CGP-12177 were biphasic, and characterized by the appearance of a population of receptors with a low affinity for both hydrophilic ligands. Furthermore, at lower temperatures the biphasic nature of these curves was accentuated and was characterized by a 6-fold and 40-fold increase in the apparent KD of a population of low affinity sites for isoproterenol and CGP-12177, respectively.

Adolescent↗
PubMed1986

Characterization of the human lymphocyte beta-adrenergic receptor by photoaffinity labeling. Alterations with desensitization.

Desensitization of the leukocyte beta-receptor system has been associated with a functional uncoupling of the components of the beta-receptor complex. In order to determine whether desensitization and uncoupling of the leukocyte beta-receptor is associated with any structural alterations in the beta-receptor, we studied labeling of lymphocytes using the photoactive beta-adrenergic antagonist p-azido-m-[125I]iodobenzylcarazolol. Labeled peptides were separated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and detected using autoradiographic techniques. In broken cell preparations, specific labeling was demonstrated in two major peptide bands: mol wt approximately equal to 68,000 and mol wt approximately equal to 55,000. Inhibition of photolabeling was stereospecific and demonstrated an order of potency for agonists consistent with labeling of a beta 2-receptor. Preincubation of cells with the beta-agonist, isoproterenol, resulted in a reduction in beta-adrenergic-mediated adenylate cyclase activity to 60% of control, but no change in total binding sites as determined by [125I]iodocyanopindolol binding. In photolabeling studies, desensitization was associated with a reduction in proportional labeling of the 55,000 mol wt band as compared to the 68,000 mol wt band to 58 +/- 3% of control and a reduction in mobility of the upper band. These studies suggest that structural alterations in the human lymphocyte beta-receptors occur with desensitization, analogous to changes in several other beta-receptor model systems. Also, since the techniques described can identify alterations in human beta-receptor structure, these methods may be exploited to determine whether structural alterations in lymphocyte beta-receptors may occur in human disease states.

Adenylyl Cyclases↗
PubMed1986

In vivo regulation of beta-adrenergic receptors on human mononuclear leukocytes: assessment of receptor number, location, and function after posture change, exercise, and isoproterenol infusion.

We studied the regulation of beta-adrenergic receptors in human mononuclear leukocytes (MNL). Total receptor number was determined as specific binding at 4 C of [3H] dihydroalprenolol or [125I]iodopindolol, and redistributed receptors were defined as those binding sites to which the hydrophilic antagonist CGP-12177 did not have access. Receptor function was assessed as cAMP accumulation stimulated by isoproterenol. In in vitro experiments, high concentrations of isoproterenol desensitized receptor function and promoted redistribution of about 80% of the receptors away from the cell surface. However, three in vivo protocols (upright posture for 3 h, moderate exercise, and infusion of isoproterenol for 30 min) redistributed few beta-adrenergic receptors on MNL. The 30-min isoproterenol infusion did not alter later cAMP accumulation, but posture change and exercise increased isoproterenol-stimulated cAMP accumulation in intact MNL. Infusion of isoproterenol for 120 min redistributed 9 +/- 2% (+/- SEM) of the receptors and decreased isoproterenol-stimulated cAMP accumulation by 19 +/- 6%. Isoproterenol-stimulated adenylate cyclase activity in membranes isolated from MNL previously was found to be decreased with upright posture, and we confirmed these findings in assays that did not include exogenous GTP, but instead relied upon guanine nucleotides retained in the membrane preparation. However, when excess GTP was included, isoproterenol-stimulated adenylate cyclase activity in MNL membranes was not altered by posture change. We conclude that substantial receptor redistribution of beta-receptors on MNL does not readily occur in physiological situations.

Adenylyl Cyclases↗
PubMed1986

Phenylarsine oxide inhibits agonist-induced changes in photolabeling but not agonist-induced desensitization of the beta-adrenergic receptor.

In the human lymphocyte, desensitization of the beta-adrenergic receptor-adenylate cyclase complex is associated with sequestration of the receptor as well as a change in photolabeling of beta-receptor proteins. Thus, desensitization of the lymphocyte beta-adrenergic receptor-adenylate cyclase system is associated with a selective reduction in the photoaffinity labeling of an Mr approximately equal to 55,000 beta-adrenergic receptor-binding site as compared to an Mr approximately equal to 68,000 beta-adrenergic receptor-binding moiety. In order to examine the relationship between sequestration and reduction in labeling of the Mr approximately equal to 55,000 peptide, we have studied the effect of phenylarsine oxide (an inhibitor of beta-receptor sequestration in astrocytoma cells) on agonist-induced desensitization of the beta-adrenergic receptor-adenylate cyclase system in circulating lymphocytes. Incubation of cells with phenylarsine oxide prior to exposure to agonists did not block the consequent reduction in isoproterenol-stimulated adenylate cyclase activity. However, sequestration of the receptor, as assessed by a decrease in accessibility of beta-adrenergic receptors on intact cells to hydrophilic receptor ligands, is blocked by phenylarsine oxide. Thus, the agonist-induced reduction in binding of the hydrophilic beta-adrenergic receptor ligand CGP-12177 was blocked by phenylarsine oxide (without phenylarsine oxide, 57 +/- 6% of control, with phenylarsine oxide, 97 +/- 3% of control). Photolabeling studies with [125I]iodocyanopindolol diazirine revealed that phenylarsine oxide pretreatment also blocked the selective loss in labeling of the Mr approximately equal to 55,000 beta-adrenergic receptor protein. These data suggest that agonist-induced alterations in the photolabeling pattern of the lymphocyte beta-adrenergic receptor that occur with desensitization closely parallel the apparent sequestration of beta-adrenergic receptors but can be dissociated from the initial desensitization phenomenon.

Adenylyl Cyclases↗
PubMed1986

Physiological and molecular correlates of age-related changes in the human beta-adrenergic receptor system.

Aging decreases hormone responsiveness in several receptor systems. In this article I consider both physiological and biochemical studies supporting the hypothesis that beta-adrenergic receptor responsiveness is reduced with aging in humans. Reduced chronotropic and vasodilator responses to the beta-receptor agonists isoproterenol and metaproterenol have been demonstrated. In human leukocytes a reduction in adenylate cyclase (EC 4.6.1.1) activity occurs with aging. More recently it has been suggested that this reduction in beta-adrenergic responsiveness with aging may be caused by an uncoupling of the beta receptor from the catalytic component.

Aging↗
PubMed1985

Lack of effect of oral activated charcoal on imipramine clearance.

The effect of oral activated charcoal on the pharmacokinetics of intravenous imipramine was studied in a randomized, crossover trial. Four normal men received intravenous imipramine (12.5 mg/70 kg) on two separate occasions, followed by either water or water plus high-surface-area activated charcoal (180 gm) in divided doses over 24 hours. Serum imipramine concentrations were measured from 0 to 24 hours after the imipramine infusion. There was no difference in the mean (+/- SE) t1/2 (9.0 +/- 0.8 vs. 10.9 +/- 1.6 hours), apparent volume of distribution (11.2 +/- 2.1 vs. 12.4 +/- 2.1 L/kg), or systemic clearance (992.2 +/- 138.3 vs. 930.3 +/- 101.9 ml/min/70 kg) of imipramine after dosing without and with oral activated charcoal, respectively (P greater than 0.05; paired t test). These results suggest that multiple oral doses of activated charcoal do not increase the clearance of imipramine in man.

Absorption↗
PubMed1985

The interaction of verapamil and norverapamil with beta-adrenergic receptors.

To determine the effect of calcium-channel blockers on beta-adrenergic receptors, we studied the interactions of verapamil, diltiazem, and nifedipine with both human lymphocyte beta 2-adrenergic receptors and rat myocardial beta 1-adrenergic receptors by means of radioligand binding assays. We also determined the functional consequences of these interactions by measuring adenylate cyclase activity. Radioligand binding studies in vitro demonstrated a Ki of verapamil for the lymphocyte beta 2-receptor of 32 +/- 4 microM. Diltiazem and nifedipine were much less potent. In studies of adenylate cyclase activity, verapamil was shown to act as a competitive beta-receptor antagonist. Also, norverapamil, the active metabolite of verapamil, had the highest affinity for the beta-receptor of any of the calcium-channel blockers studied (Ki = 4.2 +/- 0.8 microM). After 1 week of verapamil administration in six normal subjects, isoproterenol-stimulated adenylate cyclase activity in lymphocytes was increased from 60 +/- 4% to 83 +/- 10% over basal activity (p less than .05). This was associated with an increase in lymphocyte beta-receptor affinity for agonist as represented by the decrease in the IC50 for isoproterenol inhibition of [125I] iodocyanopindolol binding from 240 +/- 20 to 170 +/- 10 nM (p less than .05). Additionally, plasma norepinephrine levels were reduced from 206 +/- 58 to 92 +/- 18 pg/ml with 1 week of verapamil treatment (p less than .05). Our data suggest that verapamil affects lymphocyte beta-receptors in vitro and with long-term administration regulates lymphocyte beta-receptor function either directly or indirectly via a reduction in plasma catecholamine levels.

Adenylyl Cyclases↗
PubMed1985

The effects of activated charcoal on digoxin and digitoxin clearance.

The effect of multiple oral doses of activated charcoal on digitalis glycoside kinetics was studied to determine whether an activated charcoal regimen might have utility in treating patients with digitalis toxicity. Normal subjects were given intravenous infusions of digoxin 0.75 mg/70 kg or digitoxin 1 mg/70 kg iv followed by either water alone or water with activated charcoal in divided doses in a randomized crossover design. A subject with chronic renal failure was also given digoxin 0.5 mg/70 kg iv followed by water alone or water with activated charcoal. In six normal subjects, treatment with activated charcoal did not increase digoxin clearance (Cl) significantly (16.79 +/- 1.70 vs. 22.68 +/- 3.51 L/h). However, digitoxin Cl did increase significantly, from 0.24 +/- 0.01 to 0.47 +/- 0.04 L/h. In the renal failure subject, digoxin Cl increased from 3.6 L/h to 10.1 L/h. We conclude that the activated charcoal regimen is probably useful in patients with digitoxin toxicity. Although similar benefit is limited in patients with normal renal function who develop digoxin toxicity, it is possible that activated charcoal will be useful in patients with prolonged digoxin elimination due to renal dysfunction.

Adult↗
PubMed1984

Alterations in leukocyte beta-receptor affinity with aging. A potential explanation for altered beta-adrenergic sensitivity in the elderly.

The elderly have reduced beta-adrenergic sensitivity to agonists, but no change in receptor density. We investigated the relation between beta-receptor affinity for agonists and age in beta-receptors on lymphocytes from 20 healthy men 21 to 74 years old. As an index of beta-receptor affinity for agonists, we determined the IC50 of isoproterenol--the concentration of isoproterenol required to inhibit 50 per cent of iodohydroxybenzylpindolol binding in vitro. We found that receptor affinity for agonists was correlated with age and plasma norepinephrine concentration. Twelve subjects (six 21 to 29 years old and six 55 to 74 years old) were also studied in both the supine and upright positions. In samples obtained in the supine position, the proportion of receptors binding agonist with a high affinity was decreased in the older subjects as compared with the young subjects (22 +/- 1 per cent vs. 38 +/- 3 per cent; P less than 0.05). With upright posture and the associated acute elevation of endogenous plasma catecholamines, the proportion of receptors binding agonist with a high affinity was reduced in the young; no such changes were seen in the older subjects. The data suggest that reduced beta-receptor affinity for agonists may be an explanation for altered beta-adrenergic sensitivity in the elderly.

Adrenergic beta-Agonists↗
PubMed1984

Leukocyte beta-receptor alterations in hypertensive subjects.

It has been suggested that beta-adrenergic responsiveness is reduced in hypertension. To evaluate a possible alteration in human beta-receptors that might account for diminished beta-adrenergic responsiveness, we studied leukocytes from hypertensive and normotensive subjects after an overnight rest supine, and then after being ambulatory, a maneuver that increases plasma catecholamines approximately twofold. In supine samples, beta-receptor affinity for the agonist isoproterenol was significantly reduced in hypertensives and was associated with a reduction in the proportion of beta-receptors binding agonist with a high affinity from 42 +/- 6% in normotensive subjects to 25 +/- 2% in hypertensives (P less than 0.05). Alterations in beta-adrenergic-mediated adenylate cyclase activity parallelled the differences seen in the beta-receptor affinity for agonist. In normotensive subjects, beta-receptor density and the proportion of receptors binding agonist with high affinity were reciprocally correlated with plasma catecholamines. However, in the hypertensive subjects these correlations were not evident. Thus, our data suggest an alteration in leukocyte beta-receptor interactions in hypertensive subjects, and may represent a generalized defect in beta-receptor function in hypertension.

Adenylyl Cyclases↗