The advent of direct radioligand binding studies has altered the entire complexion of the experimental approach to the study of adrenergic recep­ tors. The first successful direct binding studies of ,8-adrenergic receptors were reported in 1974 (1-3) and those of a.-adrenergic receptors only in 1976 (4-6). Nonetheless, the application of these methods over the past several years has led to rapid progress in a number of areas. In this article we review some of the highlights of this progress. It has not been our goal to be encyclopedic or all-encompassing. Rather, we have deliberately se­ lected several areas for more extensive coverage. These choices have been, obviously, subjective ones. In general we have focused on studies that provide new insights into factors that appear to regulate the function of the adrenergic receptors, either at a physiological or biochemical level. Only material related to a.and ,8-adrenergic receptors published through the end of 1978 has been systematically considered. Several radioligand antagonists have bee n widely used to study the ,8adrenergic receptors in a variety of tissue systems. These are (-) PH]

https://www.annualreviews.org/doi/pdf/10.1146/annurev.pa.20.040180.003053

Radioligand binding studies of adrenergic receptors: new insights into molecular and physiological regulation.

We assessed the effects of exercise and beta-adrenoceptor blockade on left ventricular ejection fraction (LVEF) measured by radionuclide ventriculography in nine patients with uncomplicated hyperthyroidism. Patients were studied in both the hyperthyroid and euthyroid states. The hyperthyroid state was characterized by a high LVEF at rest but--paradoxically--by a significant fall (P less than 0.01) in LVEF during exercise. At the same workload and at the same heart rate, patients had a restoration of the normal rise in LVEF during exercise when they were euthyroid. The LVEF was greater during exercise (P less than 0.02) when the patients were euthyroid than when they were hyperthyroid. Pretreatment with propranolol caused similar reductions in resting LVEF in the hyperthyroid and euthyroid states; the drug attenuated the rise in LVEF during exercise when the patients were euthyroid, but did not influence the exercise-induced reduction in LVEF in hyperthyroidism. The abnormal left ventricular function observed during exercise in hyperthyroidism suggests a reversible functional cardiomyopathy, independent of beta-adrenoceptor activation, that is presumably a direct effect of an excess in circulating thyroid hormones.

Abnormal left ventricular function in hyperthyroidism: evidence for a possible reversible cardiomyopathy.

Biochemical and Physiologic Effects of Thyroid Hormone on Cardiac Performance

Publisher Summary Brown fat cells produce heat by oxidation of the fatty acids. Isolated cells are prepared by collagenase treatment of brown fat from hamsters and rats. The chapter outlines the isolation procedure for the brown fat cells and discusses the properties of the isolated cell suspension. The effect of the incubation conditions on the parameters such as membrane potential, lipolysis, and respiration as an indirect measure of thermogenesis are studied. Brown fat thermogenesis in vivo is stimulated by norepinephrine (NE), liberated from sympathetic nerve endings in the tissue. The hormones studied on brown fat cells can be divided into three major groups—namely, (1) the hormones that exert their effect on the brown fat cell itself; (2) the hormones that act solely by releasing stored catecholamines, within the tissue or in impure cell preparations; and (3) the hormones that only affect the tissue indirectly in the intact animal. The fatty acids released by hormone-sensitive lipase activity may be exported either as such, or activated to acyl coenzyme A (acyl-CoA) in the cell. The acetyl coenzyme A (acetyl-CoA), produced by mitochondrial β-oxidation, is further metabolized by different mitochondrial matrix enzymes. The chapter also discusses the mechanism of heat production in the brown fat cell.

The Brown Fat Cell

(Second of Two Parts) Inter-relation between Thyroid Hormone, Catecholamines and β-Adrenergic Receptors Previous speculation and many data in this area are omitted for the sake of brevity. Some of ...

T. Ciaraldi

Papers

Thyroxine and propylthiouracil effects in vivo on alpha and beta adrenergic receptors in rat heart