Neural control of adenylate cyclase responsiveness in brown adipose tissue

The level of prior adrenergic stimulation is known to affect the responsiveness of tissue to subsequent stimulation. We investigated the effects of cold exposure on sympathetic nerve activity in interscapular brown adipose tissue (IBAT) and the impact of those changes on the responsiveness of the adenylate cyclase system. Exposing rats to 4 degrees C for 3 days increased norepinephrine turnover in IBAT and increased the ability of norepinephrine to stimulate adenylate cyclase activity. This 2- to 3-fold increase in adenylate cyclase activity appeared to result from increased nerve transmission because it was abolished by prior surgical denervation of IBAT. Additional studies indicated that cold exposure did not affect the number of beta adrenergic receptors in IBAT. Moreover, cold exposure increased the maximal response of adenylate cyclase to fluoride and guanosine-5--(beta-gamma-imino)triphosphate stimulation by 2- to 3-fold. We conclude that increased nerve transmission produces supersensitivity of IBAT adenylate cyclase and this effect is mediated by a postreceptor modification of the adenylate cyclase system.