In vitro experiments on the vitellogenesis of common carp, tuna, and chum salmon show that Fsh and Lh have equivalent function in stimulating ovarian steroid production. Experiments have shown that sex steroids differentially regulate gonadotropin gene expression in the pituitary of goldfish: a strong in vivo inhibitory effect on fshb mRNA production, but a weak stimulatory effect on lhb in sexually immature and recrudescent fish. T treatment in vitro does not significantly decrease fshb mRNA levels, but increases that of lhb only in the cells of immature fish.
Human CG was used in this study because it is commercially available, very stable in solution, and has a relatively high binding affinity for gonadotropin receptors. More important, it is biologically active in fish, such as goldfish (Carassius auratus), yellow perch (Perca flavescens), and channel catfish (Ictalurus punctatus ). In our in vitro bioassays, rgLh significantly stimulated cyp19a1a and cyp19a1b gene expression and the secretion of T and E2. These results indicate that hCG can significantly increase T and E2 secretion, and that rgLh not only mimics the effect of hCG but also displays more potent action than hCG..