Pituitary gonadotropic hormone from a chondrostean fish, starred sturgeon (Acipenser stellatus Pall.) IV. Differences in biological action of isoforms and absence of sex-specific forms.

The specific activities of four subfractions of the starred sturgeon (Acipenser stellatus Pall.) pituitary gonadotropin (aci-GTH-A, -B, -C, -D) were compared using several test systems. The ratios of two of them (A and D) that contained the isoforms differing by the values of isoelectric point were shown to be different, especially when in vitro oocyte maturation and spermiation tests were used. These differences were not due to the presence in one of these preparations of the component affecting spermiation rather than oocyte maturation. The qualitative differences in the biological action of aci-GTH-A and -D were also revealed by the comparison of dose-response curves using toad oocyte in vitro maturation. Finally, as the spectra of aci-GTH isoforms were practically identical when female or male individual pituitary extracts were submitted to isoelectric focusing, we concluded that the structural and functional heterogeneity of aci-GTH was related neither to sex nor to genetic intrapopulation polymorphism.