Transepithelial transport of K+, NH4+, inorganic phosphate and water by hen (Gallus domesticus) lower intestine (colon and coprodeum) perfused luminally in vivo

Abstract

The colon and coprodeum of anaesthetised laying hens was perfused luminally with solutions of varying compositions to elucidate the influence of three levels of dietary Na+ and of luminal fluid composition on transport of electrolytes and water. Net rates of secretion of K+ and absorption of NH4+ were increased in response to dietary Na+ depletion and increased luminal Na+ concentrations, but these fluxes were linked to Na+ transport and no dietary or perfusion treatment effects could be detected on them independently of effects on Na+ flux. Similar results were found for Na+-linked water absorption from isosmotic perfusates. Serosal-mucosal net osmotic flow with Na+-free perfusates was significantly reduced by Na+-depletion, but no significant dietary effect could be detected on the serosal-mucosal osmotic permeability coefficient. The reflexion coefficient was effectively unity. Mucosal-serosal inorganic phosphate flux was small. The flux was independent of Na+ flux and dietary Na+ levels, and apparently facilitated by serosalmucosal osmotic flow. The data allowed determination of the absorption/secretion in coprodeum and colon of the ions investigated, as compared to the renal excretion rate.