EFFECTS OF VARIOUS ADENOHYPOPHYSEAL HORMONES OF CHUM SALMON ON THYROXINE RELEASE INVITRO IN THE MEDAKA, ORYZIAS-LATIPES

Effects of various adenohypophysial hormones isolated from the chum salmon pituitary as well as crude pituitary extract of chum salmon on thyroxine release in vitro were examined in adult female medaka, Oryzias latipes. Tissues of the lower throat region containing thyroid follicles were incubated in static culture using a defined medium. Bovine thyroid stimulating hormone (TSH) and the pituitary extract stimulated thyroxine release in a dose-related manner. In contrast, chum salmon growth hormone, prolactin, and gonadotropins I and II did not stimulate the release of thyroxine. These results suggest that this in vitro incubation can be used as a specific bioassay for teleost TSHs. It may also provide a useful model for further study of teleost thyroid function.