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COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

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

¹Department of Zoology, University of Otago, Dunedin, New Zealand; and ²School of Aquatic and Fishery Sciences, University of Washington, Seattle, Washington

Submitted 2 November 2004 ; accepted in final form 26 January 2005

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 µg/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 µg/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.

teleost; Oncorhynchus nerka; osmoregulation; pyloric ceca

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