HEMODYNAMIC-EFFECTS OF L-GLUTAMATE IN NTS OF CONSCIOUS RATS - A POSSIBLE ROLE OF VASCULAR NITROSYL FACTORS

This study examined peripheral mechanisms responsible for changes in m ean arterial blood pressure, heart rate, and renal, mesenteric, and hi ndquarter vascular resistances produced by microinjections of L-glutam ate (L-Glu) into the nucleus tractus solitarii (NTS) of conscious rats . Microinjection of L-Glu produced an initial presser response, bradyc ardia, and vasoconstriction in each vascular bed. Subsequent hindquart er vasodilation was observed. After prazosin was administered, L-Glu p roduced initial hypotension that was probably due to reduced cardiac o utput. This hypotension was followed by hindquarter vasodilation. Inhi bition of nitric oxide synthesis did not affect the initial hypotensio n or bradycardia in rats treated with prazosin, but the first microinj ection of L-Glu after administration of prazosin and N-G-nitro-L-argin ine methyl ester (L-NAME) produced significantly greater hindquarter v asodilation than after administration of prazosin alone. Second and th ird microinjections of L-Glu produced significantly smaller hindquarte r vasodilation. We conclude that 1) hemodynamic effects produced by mi croinjection of L-Glu into the NTS of conscious rats involves activati on of the sympathetic nervous system and 2) release of preformed nitro syl factors may mediate vasodilation in the hindquarter vascular bed.