THE EFFECT OF ATRIAL-NATRIURETIC-PEPTIDE ON INTESTINAL ELECTROLYTE TRANSPORT

The effect of atrial natriuretic peptide (ANP) on rat small intestinal electrolyte transport was examined. In vivo, intravenous administration of rat ANP(99-126) induced diuresis and natriuresis in conjunction with a significant decrease in intestinal water (basal, 37.1 +/- 5.7 versus ANP 28.5 +/- 6.0-mu-l/cm per 20 min, P < 0.05) and Na+ (4.0 +/- 0.7 versus 2.8 +/- 0.9-mu-mol/cm per 20 min, P < 0.05) absorption (n = 9). In vitro, in Ussing chambers, in both jejunum and ileum, addition of 1.0-mu-M ANP to short circuited, stripped tissue produced a maximal increase in short circuit current and stimulated net Cl- secretion due to a significant increase in the unidirectional serosal to mucosal flux (J(sm)Cl-: jejunum 17.4 +/- 1.3 versus 19.8 +/- 1.3-mu-Eq/cm2 per h, P < 0.01, n = 6; ileum 13.4 +/- 0.5 versus 17.2 +/- 0.6, P < 0.01, n = 6) which was inhibited by the calcium channel antagonist verapamil (82 +/- 26%, P < 0.05) and by the 5-HT2 receptor antagonist cinanserin (72 +/- 44%, P < 0.05). Guanylate cyclase activity was stimulated by ANP in intact epithelium, but not in isolated crypt and villus enterocytes.