Increased duodenal HCO3- output after blood volume expansion in the rat: an effect mediated by atrial natriuretic peptide (ANP)?

Duodenal HCO3- secretion was measured by in-situ titration in chloralose-anaesthetized rats. The effects of hypervolaemia, induced by i.v. injections of an albumin infusion, on duodenal HCO3- secretion were investigated. A 10% increase in blood volume increased duodenal HCO3- secretion by about 50%, and this effect was unaffected by splanchnicotomy. If the splanchnicotomy was combined with cervical vagotomy, the basal HCO3- secretion was lower but the increase in secretion after 10% blood volume expansion with albumin was still 50%. If the same increase in blood volume was produced in splanchnicotomized and vagotomized rats in which the right atrial appendix had been removed, a procedure that markedly reduces the ANP (atrial natriuretic peptide)-producing cells, no increase in secretion could be observed. Intravenous injections of alpha-r-ANP (10 micrograms kg-1 and 30 micrograms kg-1) increased duodenal HCO3- secretion in a dose-dependent fashion. Based on the present findings, we suggest that hypervolaemia increases duodenal HCO3- secretion via release of ANP from the heart.