Alpha 2-adrenergic receptors in brown adipose tissue of infant rats--I. Identification and characteristics of binding sites in isolated plasma membranes.

1. Alpha 2-Adrenoceptor antagonists [3H]yohimbine and [3H]RX 781094 and the partial alpha 2-agonist [3H]clonidine exhibited specific binding to plasma membrane fragments isolated from interscapular brown fat of 7-day-old rats. 2. Competition studies with epinephrine, yohimbine and practolol revealed that [3H]norepinephrine, the principal in vivo agonist acting upon brown adipocytes, can readily bind to alpha 2-adrenoceptors in brown fat of infant rats. 3. The presence of alpha 2-adrenoceptor subclass in brown fat of infant rats may play a role in the sympathetic regulation of this rapidly proliferating tissue.