Gonadotropin receptors in the postovulatory ovary of amago salmon (Oncorhynchus rhodurus).

Highly purified 125I-labeled chum salmon, Oncorhynchus keta, gonadotropin (GTH; CSG-SII) demonstrated specific binding to membrane fractions prepared from amago salmon (Oncorhynchus rhodurus) postovulatory ovary. Previously these ovaries had been reported to produce steroid hormones in response to GTH stimulation. Maximum specific binding occurred at pH 7 to 8 after 18-24 hr of incubation at 4 degrees in the presence of 40 mM Ca2+. As the concentration of labeled hormone increased, specific binding to the membrane preparation of the postovulatory ovary approached saturation. NIH ovine LH and FSH partially inhibited the specific binding of CSG-SII to the GTH receptors, but chum salmon growth hormone, prolactin, and alpha-MSH did not displace the binding. These results provide evidence for the existence of specific and saturable GTH receptors in the postovulatory ovary of amago salmon.