Distribution and function of brain natriuretic peptide in the stomach and small intestine of the rat.

The distribution and function of brain natriuretic peptide (BNP) was studied in the rat stomach and jejunum. BNP-like immunoreactive nerves were found in the myenteric plexus, circular muscle, submucosa and in the crypt region of the jejunum. In the stomach, BNP-like immunoreactivity was found in the myenteric plexus, circular muscle, submucosa and at the base of the gastric glands. In the submucosa, BNP-like immunoreactivity was often associated with blood vessels. In segments of rat jejunum mounted in Ussing chambers, serosal exposure to rat BNP caused a concentration-dependent increase in short circuit current. A maximal effect of 18 +/- 4 microA/cm2 was observed with 1 microM BNP. The effect was quantitatively and qualitatively similar to that elicited by serosal exposure to equimolar atrial natriuretic peptide. The response to BNP was reduced by 88% in chloride free Kreb's buffer, by 83% in tissues pretreated with cinanserin, an antagonist of the 5-HT2 subtype of the 5-hydroxytryptamine receptor, and by 96% in tissues pretreated with tetrodotoxin, a blocker of axonal conduction. These results are consistent with a physiological role for BNP as a neuromodulator of gastrointestinal electrolyte transport.