ANP INDUCES WATER AND ELECTROLYTE SECRETION IN THE IN VIVO RAT PERFUSED JEJUNUM

Abstract

Atrial natriuretic peptide (ANP) is involved in the renal regulation of water and electrolyte homeostasis. ANP exerts its effects through the stimulation of the guanylate cyclase (GC)-cGMP system. Conflicting data have been reported concerning the effects and the mechanism of action of ANP in the intestine. Aims of the work were: 1) to see whether ANP affects the intestinal water and electrolyte transport and 2) to investigate its mechanism of action and namely the binding of ANP to intestinal cells or membranes and its effects on the GC-cGMP system. Intravenous administration of ANP (0.3ug/Kg/30min) resulted in a significant shift of water, sodium and chloride absorption toward secretion in the vivo perfused rat jejunum. Such effect was prompt, but of short duration (less than 10 minutes on a continued ANP infusion). No effect was observed on potassium transport. The effects of the addition of 3-28 rat ANP in a concentration range of 10−8 to 10−SM on GC and on cGMP were studied using rat jejunal homogenates and rat jejunal cells. GC and cGMP were measured at various times after the addition of ANP. 2 minutes after the addition on ANP, a modest (1.5 times) increase of both GC and cGMP was observed which rapidly returned to basal levels. No specific binding was obtained by incubating 125I-ANP with basolateral membranes, cells or homogenates prepared from rat jejunum. We conclude that ANP may play a role as a short-lived modulator in the intestinal regulation of water and electrolyte homeostasis. The mechanism of such interaction appears to be indirect, since it does not involve the GC-cGMP system nor is mediated by specific binding sites on the enterocyte.