Somatolactin stimulates in vitro gonadal steroidogenesis in coho salmon, Oncorhynchus kisutch.

Somatolactin (SL), a newly discovered pituitary hormone of the teleost pars intermedia, is structurally similar to prolactin and growth hormone. The function(s) of SL are not yet established, although evidence suggests that it may play a role in reproduction. Possible steroidogenic activity of coho salmon SL was tested and compared with gonadotropin I (GTH I) in incubations of ovarian follicles or testicular fragments. SL stimulated production of 11-ketotestosterone and testosterone by testicular fragments, and production of estradiol by ovarian follicles in a concentration-dependent manner. However, the steroidogenic activity of SL was considerably less than that of GTH I. These results suggest that SL may play a role in regulation of gonadal function in salmon.