MODULATION OF BROWN ADIPOSE TISSUE-MEDIATED THERMOGENESIS BY LESIONS TO THE NUCLEUS TRACTUS SOLITARIUS IN THE RAT

Given that relatively little is known regarding the central control of brown adipose tissue (BAT)-mediated thermogenesis the present study assessed whether the direct pharmacological stimulation of beta- or alpha-adrenergic receptors located on the brown adipocytes would result in a typical thermogenic response following electrolytic lesions to the nucleus tractus solitarius (NTS). Bilateral electrolytic lesions to the NTS in the rat effectively disrupted the baroreceptor reflex arc. It was observed that the metabolic and temperature responses to either norepinephrine (1, 5, or 25-mu-g/kg/min) or to the beta-agonist isoproterenol (0.5-mu-g/kg/min) were significantly attenuated in the NTS-lesioned (0.5-mu-g/kg/min) were significantly attenuated in the NTS-lesioned rats relative to the control animals with an intact baroreflex. Conversely, the cardiovascular effects of norepinephrine or of the alpha-agonist phenylephrine (10-mu-g/kg/min) were enhanced in the NTS-lesioned animals. The results suggest that the functional capacity of the brown adipocytes was reduced following NTS lesions and points to an alteration in the ability of beta-receptors to respond to pharmacological stimulation with a typical thermogenic response.