POSSIBLE INVOLVEMENT OF L-ARGININE-NITRIC OXIDE PATHWAY IN MODULATINGREGIONAL BLOOD-FLOW TO BROWN ADIPOSE-TISSUE OF RATS

To evaluate whether the L-arginine-nitric oxide (NO) pathway is involv ed in the regulation of regional blood flow to brown adipose tissue (B AT), the effects of two specific NO synthase inhibitors, N-G-nitro-L-a rginine methyl ester (L-NAME) and N-G-monomethyl-L-arginine (L-NMMA), on the blood flow to interscapular brown adipose tissue (IBAT) were st udied in urethane-anesthetized rats. Regional blood flow in IBAT was m easured with laser-Doppler flowmetry. An intravenous injection of L-NA ME and L-NMMA, but not of either D-enantiomer, caused a transient and dose-dependent increase in IBAT blood flow Dose-response curves for th ese NO synthase inhibitors showed that L-NAME was more potent than L-N MMA in increasing IBAT blood flow. We also observed a concomitant pres ser effect accompanied by a slight decrease in heart rate following in travenous injection of L-NAME and L-NMMA. An elevation of IBAT blood f low and blood pressure induced by both L-NAME and L-NMMA was reversed by L-arginine in an enantiomerically specific manner. The increase in IBAT blood flow induced by NO synthase inhibitors was of shorter durat ion and less sensitive to L-arginine than the increase in blood pressu re. Our results show that the IBAT blood flow is increased by inhibiti on of NO synthase and that the response of IBAT vasculature to NO synt hase inhibitors is different from that of the resistance vessels which regulate blood pressure. The involvement of L-arginine-NO pathways in modulating microcirculation in IBAT is suggested.