DIRECT STIMULATION OF BAT THERMOGENESIS DOES NOT AFFECT HYPOTHALAMIC NEUROPEPTIDE-Y

Acute cold exposure which significantly stimulated thermogenesis in br own adipose tissue (BAT), also increased neuropeptide Y (NPY) levels i n its hypothalamic sites of release without affecting NPY synthesis, s uggesting that NPY release is acutely inhibited. To clarify whether th ese changes in NPY are the cause or consequence of BAT activation, we studied whether hypothalamic NPY and NPY mRNA levels in rats were affe cted by acute intraperitoneal injection of the beta(3)-adrenoceptor ag onist BRL 35135 (500 mu g/kg), which directly activates BAT thermogene sis. BRL. 35135 treatment doubled BAT uncoupling protein mRNA levels ( p < 0.05), and increased core temperature by 0.4 degrees C (p < 0.05), but neither hypothalamic regional NPY levels nor hypothalamic NPY mRN A levels were affected by BRL 35135. This suggests that the NPY change s induced by cold exposure are not the result of BAT activation, and i s consistent with the hypothesis that decreased NPY release during col d exposure might disinhibit the sympathetic innervation that drives BA T thermogenesis. (C) 1998 Elsevier Science Inc.