Occurrence of alpha 2-adrenergic effects on adenylate cyclase activity and (3H)-clonidine specific binding in brown adipose tissue from foetal rats.

Noradrenaline maximally stimulates adenylate cyclase activity in brown adipocytes from foetal rats by 400%. Isoproterenol maximally stimulates the adenylate cyclase activity by 600%. The differences observed in the dose-response curves of adenylate cyclase activity to isoproterenol or noradrenaline were prevented in the presence of clonidine (a alpha 2-agonist) or yohimbine (alpha 2-antagonist) respectively. (3H)-clonidine binds specifically to brown fat membranes saturable (from 1.75 to 20 nM). Scatchard analysis revealed a Bmax of 22 fmol/mg and a KD of 10 nM.