Equine follicle-stimulating hormone action in cultured Sertoli cells from rat, sheep and pig.

Using a suspension of seminiferous tubule cells, we had previously shown that equine FSH is superactive in the male rat, i.e. that it exhibits a higher biological potency than expected from its binding activity. In this work we investigated equine FSH superactivity in rat, pig and sheep, by comparing in each species the equine FSH with the homologous FSH, both for their binding activities (in a radioreceptor assay using a testicular membrane fraction) and for their in vitro biological potencies (in a plasminogen activator assay using a Sertoli cell-enriched population cultured on plastic). In the rat, the binding activity of equine FSH was identical to that of rat FSH, and the biological potency of equine FSH was 47 times higher than that of rat FSH. Hence, superactivity of equine FSH was confirmed in the rat. In the pig, equine FSH was not superactive, since it exhibited binding activity and biological potency identical to those of porcine FSH. In the sheep, the binding activity of equine FSH was 6 times higher than that of ovine FSH, and its biological potency was also higher (14 times). Therefore, equine FSH cannot be considered superactive in this species. In conclusion, equine FSH superactivity is closely related to the species from which Sertoli cells are isolated.