Tissue culture of sockeye salmon intestine: functional response of Na+-K+-ATPase to cortisol

A method to culture tissue explants of the intestine from freshwater-adapted sockeye salmon (Oncorhynchus nerka) was developed to assess possible direct effects of cortisol on Na(+)-K(+)-ATPase activity. As judged by several criteria, explants from pyloric ceca and the posterior region of the intestine remained viable during short-term (6-day) culture, although Na(+)-K(+)-ATPase activity declined and basolateral components of the enterocytes were observed to be partially degraded. Addition of cortisol to the culture medium maintained Na(+)-K(+)-ATPase activity (over 2-12 days) above that of control explants and, in some cases, was similar to levels before culture. The response to cortisol was dose dependent (0.001-10 microg/ml). Within the physiological range, the response was specific for cortisol and showed the following hierarchy: dexamethasone >/= cortisol > 11-deoxycortisol > cortisone. Insulin maintained Na(+)-K(+)-ATPase activity over controls in explants of ceca but not posterior intestine. To compare in vivo and in vitro responses, slow-release implants of cortisol (50 microg/g) were administered to salmon for 7 days. This treatment elevated plasma cortisol levels and stimulated Na(+)-K(+)-ATPase activity in both intestinal regions. The results demonstrate that the teleost intestine is a direct target of cortisol, this corticosteroid protects in vitro functionality of Na(+)-K(+)-ATPase, and explants retain cortisol responsiveness during short-term culture.