The effects of hypophysectomy and of hormone treatments on the interrenal of Tilapia mossambica were studied, utilizing measurements of mean interrenal nuclear diameter as an index of interrenal function.
Hypophysectomy of Tilapia maintained in isotonic Ringer's solution resulted in a significant decrease in interrenal nuclear diameter after 21 days. This decrease was prevented by treatment of hypophysectomized fish with mammalian ACTH. Mammalian ACTH significantly increased the interrenal nuclear diameters of intact fish maintained in fresh water, but failed to do so in intact Tilapia kept in isotonic Ringer's solution.
Administration of cortisol acetate to intact Tilapia reduced the mean nuclear diameter of interrenal cells. The degree of response was both dose and time dependent. Administration of 0.04 mg/day of deoxycorticosterone acetate for 21 days also significantly reduced the mean interrenal nuclear diameter. Treatment with the same dose of DCA for only 14 days, or with a smaller dose for 21 days, failed to induce interrenal atrophy.
These results suggest that a pituitary-interrenal axis, resembling the pituitaryadrenocortical axis of mammals, exists in Tilapia mossambica.