Neural Control of the α-Subunit of GsMessenger Ribonucleic Acid in Rat Brown Adipose Tissue*

Abstract

Neural stimulation of rat interscapular brown adipose tissue (IBAT) can greatly modify transmembrane signalling in this tissue. As part of an investigation into the molecular mechanisms of such modulation we have examined the effects of surgical denervation of BAT and cold exposure (a treatment that increases neural stimulation of BAT) on the levels of mRNA encoding for the .alpha.-subunit of Gs, the GTP-binding protein that regulates adenylate cyclase. The G.alpha.s mRNA content of BAT per unit RNA was 5-10 times greater than that of lung, liver, or caudate-putamen. Surgical denervation of BAT of warm-adapted rats reduced G.alpha.s mRNA content by 30% within 8 h postsurgery and by 65% by 72 h. Concurrent infusion of norepinephrine completely prevented the denervation-induced decline in G.alpha.s mRNA at 72 h. Infusion of the .beta.-adrenergic agonist isoproterenol also prevented the denervation-induced decline in G.alpha.s mRNA, but infusion of the .alpha./a-adrenergic agonist phenylephrine was without effect. Exposing rats to 4 C for 3 days approximately doubled the level of G.alpha.s mRNA. Interestingly, surgical denervation did not prevent the cold-induced increase in G.alpha.s mRNA levels, indicating that this effect is independent of local innervation. Despite reducing G.alpha.s mRNA levels by about 60%, surgical denervation failed to alter the concentration of G.alpha.s protein in IBAT membranes of warm-adapted rats, as determined by immunoblotting. Previous work indicates that cold exposure does not increase the concentration of G.alpha.s in IBAT membranes. Taken with the present results, these data indicate that there is no simple relationship between tissue G.alpha.s mRNA content and membrane G.alpha.s concentration in IBAT.