MECHANISMS UNDERLYING STIMULATION OF GASTRODUODENAL HCO3- SECRETION BY N-G-NITRO-L-ARGININE METHYL-ESTER, AN INHIBITOR OF NITRIC-OXIDE SYNTHASE, IN RATS

We investigated the mechanism underlying stimulation of HCO3- secretio n by the nitric oxide (NO) synthase inhibitor N-G-nitro-L-arginine met hyl ester (L-NAME) in the gastroduodenal mucosa of anesthetized rats. A chambered stomach (in the presence of omeprazole) or a duodenal loop was perfused with saline, and HCO3- secretion was measured at pH 7.0 by a pH-stat method. Intravenous administration of L-NAME increased ga stroduodenal HCO3- secretion with a concomitant rise in arterial blood pressure and a decrease in heart rate, and the changes were all antag onized by simultaneous administration of L-arginine. Vagotomy had no e ffect on the increased blood pressure response, but significantly inhi bited the decrease of heart rate and increase of HCO3- secretion cause d by L-NAME. The HCO3- stimulatory action of L-NAME was also inhibited by prior administration of yohimbine or prazosin. These agents alone lowered blood pressure and reduced the magnitude of the blood pressure response caused by L-NAME, leading to inhibition of heart rate change s. When Delta HCO3- output induced by L-NAME was plotted against Delta blood pressure change (from basal values) under various conditions, a significant relationship was found between these two factors. These r esults suggest that L-NAME stimulates gastroduodenal HCO3- secretion i n association with the inhibition of endogenous NO production, and thi s mechanism may be in part mediated by a neural reflex through the vag al efferent nerve, resulting from the presser response to L-NAME.