Walton W. Dickhoff J. Duston R. S. Nishioka H. A. Bern S. D. McCormick 1991 <p><span>The ability of cortisol to increase gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity was examined in several salmonid species during development. Coho salmon (</span><i>Oncorhynchus kisutch</i><span>) parr were unresponsive to cortisol&nbsp;</span><i>in vitro</i><span>&nbsp;(10 μg/ml for 2 days) in November. Responsiveness was significant from January to March, peaking in January just prior to seasonal increases in gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity. Gill tissue became unresponsive to&nbsp;</span><i>in vitro</i><span>&nbsp;cortisol in April when&nbsp;</span><i>in vivo</i><span>&nbsp;gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity peaked. The ability of cortisol to stimulate gill, Na</span>⁺<span>, K</span>⁺<span>-ATPase activity in postemergent fry (2–3 months after hatching) was examined in chum (</span><i>O. keta</i><span>), chinook (</span><i>O. tschawytscha</i><span>), coho, and Atlantic salmon (</span><i>Salmo salar</i><span>). Initial levels of gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity were elevated in chum salmon, which normally migrate as fry. Cortisol (10 μg/ml for 4 days&nbsp;</span><i>in vitro</i><span>) increased gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity in chum salmon fry (48% above initial levels), had a limited but significant effect in chinook salmon fry, and had no effect in coho and Atlantic salmon fry. In an&nbsp;</span><i>in vivo</i><span>&nbsp;experiment, Atlantic salmon previously exposed to simulated natural photoperiod (SNP) and continuous light (L24) received four cortisol injections of 2 μg · g</span>⁻¹<span>&nbsp;every third day. SNP fish responded with increased gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity (+66%), whereas L24 fish were not affected. Atlantic salmon presmolts with initially low levels of gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity responded to cortisol&nbsp;</span><i>in vitro</i><span>, whereas smolts with initially high levels of gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity were unresponsive. Triiodothyronine (0.01–10 μg/ml), prolactin (0.1–10 μg/ml), growth hormone (0.1–10 μg/ml), insulin (0.01–10 μg/ml), and bovine insulin-like growth factor I (0.01–1 μg/ml) did not affect gill Na</span>⁺<span>, K</span>⁺<span>-ATPase activity&nbsp;</span><i>in vitro</i><span>, individually or with cortisol (1–10 μg/ml). Thus, changes in responsiveness to cortisol occur during salmonid development, vary among species, and may be important in the heterochrony that characterizes the parr-smolt transformation.</span></p> application/pdf 10.1016/0016-6480(91)90054-A en Elsevier Developmental differences in the responsiveness of gill Na+, K+ and -ATPase to cortisol salmonids article