Effects of hypophysectomy on coho salmon interrenal: maintenance of steroidogenic pathway and restoration of in vitro responsiveness to adrenocorticotropin after handling.

The role of the pituitary in regulating interrenal activity in coho salmon (Oncorhynchus kisutch) was examined using short- (1 week) or long- (10 week) term hypophysectomized (Hx) animals. In experiments in which Hx animals were injected with ovine growth hormone (oGH), triiodothyronine, or vehicle, plasma cortisol was significantly lower (close to non-detectable, 1 ng/ml) in vehicle-injected or hormone-treated short- and long-term Hx animals compared to vehicle-treated sham-operated (SO animals). Treatment of long-term Hx animals with oGH led to a significant increase in plasma cortisol, in comparison to other Hx groups. Interrenal responsiveness to ACTH or cAMP was not consistently affected by hypophysectomy or hormone treatment. Pregnenolone-supported cortisol production by tissue from Hx groups was at least as great as that by tissue from SO animals; production by tissue from GH-treated, long-term Hx animals was significantly greater than that by tissue from Hx or SO animals. Similar experiments utilizing handling stress (handling and anesthesia) instead of hormone injection as a variable revealed that the response of tissue from Hx animals to ACTH or cAMP was significantly reduced in the absence of handling in comparison with SO animals. However, utilization of pregnenolone as a substrate by tissue from Hx animals was no different from that by tissue from SO animals and was independent of handling. These results indicate that the maintenance of the steroid-biosynthetic pathway is pituitary independent. The decrease in tissue responsiveness to ACTH or cAMP in undisturbed Hx animals may be partially attributable to: (1) the absence of nonpituitary/nonpituitary-mediated factors that are stimulated by handling and which probably upregulate ACTH receptors and mediating systems; and/or (2) to the presence of inhibitory factors which are decreased after handling.