Functional capacity of ectopic pituitary transplants in the teleost Poecilia formosa , with a comparative discussion on the transplanted pituitary

Abstract

The capacity of the pars distalis to secrete its hormones when removed from connexions with the hypothalamus has been assessed in the teleost Poecilia formosa. Mortality, integumentary characters, body growth, fin regeneration, freshwater adaptation, liver reserves, fat stores, haematology, and the histology of the thyroid gland, interrenal tissue and ovary, have been studied in intact fish, in hypophysectomized fish, and in hypophysectomized fish bearing a pituitary homotransplant in the musculature of the caudal peduncle. Growth, fin regeneration, liver reserves, fat stores, interrenal and ovary, have been studied also in sham-hypophysectomized fish. It is concluded that the ectopic pituitary transplant in this fish secretes thyrotrophin (TSH) at a higher rate than normal, adrenocorticotrophin (. at a subnormal rate, and growth hormone (GH) only in very small amounts. The transplant secretes the prolactin-like hormone essential for freshwater adaptation, but does not secrete gonadotrophin. The extensive literature on the ectopic pituitary has been surveyed, and the present results were compared with those obtained for other vertebrate groups. The hypothalamic influence on TSH secretion in Poecilia appears to be inhibitory, in contrast to the stimulatory relationship in mammals, and the pituitary of this teleost seems to have greater autonomy in the secretion of ACTH than the mammalian gland. The hypothalamic control of GH, prolactin and gonadotrophin, however, is probably essentially the same in Poecilia as in mammals.