Enhanced response of the interrenal of coho salmon (Oncorhynchus kisutch) to ACTH after growth hormone treatment in vivo and in vitro.

The effects of ovine growth hormone (GH) on the response of the interrenal of yearling coho salmon (Oncorhynchus kisutch) to ACTH were examined in two series of experiments. In the first series, GH was administered intraperitoneally (2 micrograms/g body wt, three daily injections) to coho salmon which had not undergone the parr-smolt transformation. Animals were sacrificed 30 hr after the final injection and head kidney tissue was prepared for in vitro incubation. GH had no effect on plasma cortisol levels but tissue taken from treated fish had an enhanced sensitivity to ACTH in vitro and its steroidogenic capacity was increased. In the second series of experiments, interrenal tissue was preincubated with GH in the dose range of 10-1000 ng/ml and was then challenged with ACTH or was incubated with 1-10 microM pregnenolone. GH-pretreated tissue displayed an enhanced response to ACTH. Cortisol production by tissue pretreated with 500 ng/ml GH was significantly enhanced after incubation with pregnenolone. No significant effect of GH was found after simultaneous exposure of interrenal tissue to combinations of ACTH and GH for 3 hr. Pretreatment of interrenal tissue with salmon prolactin had no significant effect on the subsequent response of tissue to ACTH. These results indicate that GH regulates interrenal activity in coho salmon and that one probable site of action is on the biosynthetic pathway between pregnenolone and cortisol.