Gonadotropin specificity of in vitro testosterone secretion by fish testes

Abstract

Highly purified gonadotropin preparations from representatives of all four tetrapod classes and several fish were used to examine the specificity of in vitro testosterone production by minced testes from four species of teleost fish, representing three families and two orders. No consistent phylogenetic patterns emerged in either hormonal ( FSH LH ) or phylogenetic specificity in the steroidogenic response of the teleost testis. Testes of Gillichthys mirabilis (Family Gobiidae) were highly specific for all species of LH (FSHs were inactive) and they also showed a certain degree of species specificity; mammalian and amphibian LHs were much more potent than reptilian and avian LHs. In contrast, testes of Cichlasoma citrinellum and Sarotherodon mossambicus (Family Cichlidae) lacked gonadotropin specificity (most preparations of FSH and LH were about equipotent), and in C. citrinellum all species of tetrapod hormones were active within approximately the same dose range. Gonadotropins from the sturgeon (Chondrostei) were the most potent in both G. mirabilis and C. citrinellum. In Salmo gairdneri (Family Salmonidae) there was specificity for amphibian (bullforg) LH, but not for mammalian (ovine) LH. Steroid secretion by the fish testes was temperature dependent, but relative potencies of ovine LH, bullfrog LH, and sturgeon gonadotropin were not altered by incubation temperatures between 10 and 30° in G. mirabilis. As a group, the teleosts examined here differ from mammals, birds, and reptiles in their hormonal specificity (or consistent lack there of) for testicular androgen secretion; they most closely resemble the Amphibia in their high degree of interspecific variability in response to FSH and LH. The lack of predictability in this aspect of specificity as well as in species specificity in the potencies of individual types of hormones of different origins precludes generalizations about the evolutionary pattern of gonadotropin-testis interactions.