| Abstract: | In relation to decreased metabolic sensitivity to catecholamines observed, in vitro, in brown fat of cold-acclimated rats, beta-adrenergic receptors were studied in isolated cells and in a crude membrane preparation from rat interscapular brown adipose tissue. 3H] dihydroalprenolol binding had the same characteristics in both types of preparation; competition studies of 3H] dihydroalprenolol binding led to the characterization of beta 1 subtype adrenergic receptors with a lower affinity of beta-adrenergic agonists for 3H] dihydroalprenolol binding sites in membranes than that found in isolated cells. Cold acclimation produced, in isolated cells only, a decrease of 41% in the 3H] dihydroalprenolol binding sites and a beta-adrenergic agonist affinity increase. It is concluded that beta-adrenergic receptor decrease could be a factor, at the hormone receptor interaction level, in the regulation of the transmission of biological action responsible for the cold-induced decrease in catecholamine responsiveness in brown adipose tissue. For a study of the desensitization process in brown fat, isolated cells seem to offer certain advantages over a crude membrane preparation. |
