The influence of filtrability on beta-adrenergic ligand binding to membrane fragments from human erythrocytes and mononuclear leucocytes

Effect of exercise on erythrocyte beta-adrenergic receptors and plasma concentrations of catecholamines and thyroid hormones in Thoroughbred horses

The effects of exercise stress on erythrocyte beta-adrenergic receptor characteristics and plasma concentrations of adrenaline, noradrenaline and thyroid hormones were studied in Thoroughbred racehorses during rest and after exercise. Five minutes after a maximal speed race of 1200 +/- 200 m (mean +/- s.d.), both plasma adrenaline and noradrenaline concentrations increased with respect to basal values (from 2.48 +/- 0.15 to 3.83 +/- 0.27 and from 2.13 +/- 0.11 to 3.53 +/- 0.27 nmol/l respectively). The increment of adrenaline was greater in high performance (HP) as compared to low performance (LP) horses (76.9 vs. 43.5%), in accordance with the contribution of the adrenal medulla in the sympathoadrenal response to exercise. Triiodothyronine (T3), but not thyroxine (T4) levels increased 5 min after exercise (from 55.6 +/- 2.9 to 81 +/- 3.7 ng/dl and from 0.67 +/- 0.04 to 0.70 +/- 0.05 micrograms/dl respectively). No differences were observed in basal values of thyroid hormones or in the percentage of T3 increment, when comparing HP vs. LP horses. Erythrocyte membranes obtained 5 min after racing showed decreased concentrations of beta-adrenergic receptors (beta-AR) and dissociation constant as compared to basal values (50.1 +/- 7.0 vs. 95.7 +/- 12.0 fmol/mg protein and 0.97 +/- 0.24 vs. 2.04 +/- 0.3 nmol/l respectively). This temporal pattern suggest that the observed changes in beta-AR characteristics could be mediated by catecholamines, but not by thyroid hormones, in this model. This down regulation of beta-AR may act as a protecting mechanism preventing the erythrocytes from the decrease in membrane fluidity known to be provoked by adrenergic agonists. The accomplished study showed that, in the Thoroughbred horse, there is a homeostatic response to race stress, characterised by a sudden increase in plasma catecholamines and T3 and a parallel decrease in beta-AR concentration on the erythrocyte membrane. In this way the racing horse could rapidly adjust its metabolism to the exercise stress, but at the same time override one possible undesirable side-effect caused by these hormonal changes. Further studies will be required to establish performance-related differences occurring in endocrine changes.

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.

Effect of age on lymphocyte beta 2-adrenergic responsiveness

Beta-adrenergic receptor agonists and antagonists are among the most widely used classes of agents in the US today. Heterogeneity in pharmacologic response among humans exists. This article reviews the influence of age on lymphocyte beta 2-adrenergic receptor responses. Evidence obtained in humans indicates that beta-adrenergic receptor numbers on peripheral blood cells may differ, although the direction of the change is not consistent among laboratories. Drug-induced regulation of receptors either up or down appears to be similar among age groups. The affinity of beta-adrenoceptor binding sites for isoproterenol decreases with aging. Events distal to the receptor recognition site itself exhibit age-related differences, presumably due to a decrease in the coupling of beta-adrenoceptors to adenylate cyclase. Mechanisms of decreased catecholamine responsiveness during aging remain to be defined. The precise definition of these alterations may contribute useful insights into the changes that occur with aging in response to catecholamines, other hormones, and neurotransmitters.

Beta adrenoceptors of human red blood cells, determination of their subtypes

The characteristics of beta adrenergic receptors of human erythrocyte membranes were investigated using (-)125iodocyanopindolol as a radioligand. Inhibition of (-)125iodocyanopindolol specific binding was checked using either atenolol and metoprolol as beta 1 selective antagonists or ICI 118551 and IPS 339 as beta 2 selective antagonists. The results showed non linear Hofstee's plots suggesting that both beta 1 and beta 2 adrenergic receptors are present. Analysis of the data yielded a beta 1/beta 2 adrenergic receptor ratio of approximately 33/67. Thus it is concluded that beta 2 subtype is predominant on human erythrocyte membranes.