The effect of atrial natriuretic peptide on small intestinal contractility and transit

Isometric tension in response to ANF (10(-10) to 10(-4) M) was recorded from longitudinally and circularly oriented rat jejunal smooth muscle strips. Conscious, fasted rats received an IV infusion of 1.25 nmol ANF/100 g body weight in 0.5 ml normal saline and controls received saline alone. Five minutes later 10 muCi Na2 51CrO4 in 0.5 ml saline was instilled through a jejunostomy. Fifteen minutes later animals were sacrificed, and the gut divided into 8 equal segments of small intestine, cecum and remaining colon. The radioactivity of each segment was measured and a geometric center of transit determined for each group. ANF induced relaxation of longitudinally oriented strips (Tm = -72.3 +/- 10.7 mN/g, ED50 7.3 +/- 3.6 x 10(-8) M), and contraction of circularly oriented strips (Tm = 35.0 +/- 5.0 mN/g, ED50 1.3 +/- 1.0 x 10(-8) M). This response was unaffected by 10(-6) M tetrodotoxin. The geometric mean center of transit was significantly (p less than 0.001) further aboral in ANF-treated compared to control animals (intestinal segment 4.2 +/- 0.2 vs. 3.2 +/- 0.2).