The effect of hormones and peptides involved in water balance on rat colonic motility in vitro.

We have previously shown that restriction of water intake decreased stool frequency and stool weight in volunteers. The aim of this study was to investigate whether these effects of thirst could be mediated by an action of systematically released hormones on colonic smooth muscle. Using isolated colonic smooth muscle strips the effect of arginine-vasopressin (AVP), angiotensin II (ANG II) and aldosterone on rat colonic motility in vitro was investigated. AVP (10(-12)-10(-10) mol/l) and aldosterone (3 x 10(-10)-3 x 10(-8) mol/l) and physiological hormonal concentrations of ANG II (10(-13)-10(-10) mol/l) had no effect on either basal activity, direct stimulation of colonic smooth muscle or neurally stimulated contractions using carbachol 10(-7)-3 x 10(-5) mol/l or neurally stimulated contractions using electrical field stimulation at various stimulation frequencies (1-10 pps, 1 ms, 40 V). ANG II in higher concentrations (10(-7)-10(-6) mol/l) increased basal activity and neurally mediated contractions. Accordingly, ANG II (10(-6) mol/l) caused a prestimulation but did not increase the maximum contractile effect of carbachol. The response to ANG II was not affected by atropine (10(-6) mol/l). TTX (10(-6) mol/l) and N-nitro-L8-arginine (L-NNA) (3 x 10(-4) mol/l) stimulated basal muscular activity but did not affect the maximum contractile effect of ANG II. Systemic serum concentrations of AVP, aldosterone and ANG II are presumably not involved in thirst-induced colonic motility changes. The ANG II effect in higher concentrations is mediated by a direct stimulatory smooth muscle effect and/or by facilitating neuronal liberation of acetylcholine.(ABSTRACT TRUNCATED AT 250 WORDS)