Saina Sachdev

Adrenoceptor Interplay in the Regulation of Adipocyte Metabolism

Started Mar. 1, 2023

Abstract or project description

Catecholamines affect fat metabolism in a variety of ways through the mobilisation of five adrenoceptor subtypes (β1, β2, β3, α1 & α2). Selective and non-selective β adrenoceptor agonists stimulate lipolysis while α2 adrenoceptor agonists inhibit lipolysis. Since, β and α2 adrenoceptors produce antagonistic effects, the balance between activation and inactivation of these adrenoceptors defines the net outcome of catecholamine-induced adipocyte metabolism in humans. The coexistence of these receptors on the same cell is puzzling and raises a question about its functional significance. Since, α2 adrenoceptors can be activated at low catecholamine-concentrations, a plausible theory regarding this question is that a permanent inhibition of lipolysis exists during basal conditions. Analysis of factors like the count of adrenoceptors on a cell, their differential affinities and their susceptibility to desensitisation backs up this theory. Another possibility is that these adrenoceptors may have distinct roles in different adipose tissue depots and under different pathophysiological conditions. The existence of catecholamine-resistance in the adipocytes of obese subjects is well documented. It can be attributed, in part, to a major decrease in the cell-surface density of β2 adrenoceptors. Similar differences in adipose tissue metabolism have been observed in conditions which include different body states (resting and exercise), locations of fat (subcutaneous and omental fat) and sexes etc. Many of these discrepancies can be traced back to variations in adrenoceptor activity. In this review, the interplay of adrenoceptors that generates these changes is analysed in the context of the physiology of these conditions.