Comparative effects of diverse vertebrate gonadotropins on estradiol-17 beta formation in vitro in an immature rat Sertoli cell bioassay.

The biopotencies of pituitary gonadotropins (GTHs) from various vertebrate classes were examined in an in vitro rat Sertoli cell bioassay which was previously established for mammalian follicle-stimulating hormones (FSHs). Potencies of the gonadotropins were determined by incubation of Sertoli cells obtained from 10-day-old rats, with increasing doses of GTHs, which resulted in dose-related and parallel estradiol-17 beta formation converted from added 19-hydroxy-androstenedione. In general, mammalian (human and ovine) FSHs were most potent, avian (chicken, turkey, and ostrich) FSHs were intermediate, and reptilian (snapping turtle) and amphibian (bullfrog) FSHs were the least potent. By contrast, mammalian and bullfrog luteinizing hormones (LHs) were inactive or negligibly active in this assay; avian LHs possessed one-fifth to one-half of the potency of the FSH preparations of the same species. The data suggest that the assay is specific for FSHs from mammalian and amphibian species and is relatively specific for FSHs from avian species. Both snapping turtle FSH and LH exhibited low and similar potencies in this bioassay. Black silver carp GTH was also active in this assay, although its potency was much lower. The present study has demonstrated that the immature rat Sertoli cell aromatase assay in vitro is useful for measurement of FSH contents in mammalian species and of FSH activity in diverse nonmammalian species. It also provides an approach for the investigation of structure-function relations of gonadotropin in diverse vertebrate species in relation to phylogenic patterns and specificity of hormone-receptor interaction. The findings from the present study imply that the binding sites of vertebrate FSHs share a certain degree of homology and that the binding sites of FSH receptors on Sertoli cells from immature rat have a relatively low degree of animal class specificity.