A kinetic analysis of the actions of l-noradrenaline and its related agonists and antagonists on in vitro lipolysis in rat adipose tissue

Abstract

(1) Iterative non-linearising optimisation techniques have been used to fit three alternative models to relationships between β-adrenergic effector concentrations and the lipolytic response which they elicit in dispersed adipocytes derived from rat epididymal fat pads. (2) The models, which consist of a simple hyperbolic relationship, a Hill-type function and a rational quadratic formulation, were fitted to data obtained with agonists, ‘partial’ agonists and antagonists both alone and in combination. (3) Whereas the hyperbolic relationship was inadequate in all circumstances, the Hill-type function accommodated dose-response curves which exhibit no ‘auto-inhibitory’ hook or bell-shaped feature. However, the rational quadratic function could be satisfactorily fitted to the data whether or not the auto-inhibitory phase was apparent. (4) The mechanisms that govern the steepness of the dose-response relationships and their bell-shaped feature are discussed. Evidence is presented that the latter originates at the level of adenylate cyclase.