Gonadotropin hormone (GtH) receptors in the ovary of the brown trout Salmo trutta L. in vitro studies.

A method has been developed suitable for the study of the binding of salmon (Oncorhynchus tsawytscha) gonadotropic hormone (GtH) to brown trout (Salmo trutta) ovarian particulate fractions. Several proteolytic enzyme inhibitors were tested to preserve the binding capacity of particulate fractions (1000, 20,000, and 110,000g) from yolky oocytes. The best preservation was obtained with trypsin inhibitor. The effects on binding of the pH, time, and temperature of the incubation were investigated. Binding increased linearly with amount of particulate fraction, and is saturable. In both the 20,000 and 110,000g fractions, there are two classes of receptors: one with a high-affinity constant (3.14 and 0.95 10(10) M-1 for the 20,000 and 110,000g fractions, respectively) and a low capacity (1.76 and 0.63 fmol/g of ovary), the other with a higher-affinity constant (3.44 and 1.78 10(9) M-1) but a higher capacity (7.37 and 7.42 fmol/g of ovary). GtH binding was not affected by ovine luteinizing hormone (oHL), ovine follice-stimulating hormone (oFSH), and human chorionic gonadotropin (hCG), but was partially inhibited by 1 micrograms of bovine thyroid-stimulating hormone (bTSH) and salmon prolactin (sPRL). The results are discussed in relation to the biological specificity of fish GtH and to the unsolved problem concerning the number of gonadotropins in fish.