The nature of the pituitary gonadotropins and their role in ovulation in a urodele amphibian (Ambystoma tigrinum).

Gonadotropic hormones were fractionated from pituitaries of the urodele amphibian $\text{Ambystoma}$$\text{tigrinum}$ (tiger salamander) by methods previously employed to separate these hormones in other species of tetrapod vertebrates. These procedures yielded two distinct fractions that resembled the FSH and LH from other species in regard to their biological profiles in several nonmammalian bioassays and by their chromatographic behavior. The $\text{Ambystoma}$-FSH was free of LH activity (< 0.1%). The major $\text{Ambystoma}$-LH was highly potent in ovulation assays for LH; it also had a high activity in the $\text{Anolis}$ lizard assay, but it is not clear whether this reflects high intrinsic activity or incomplete separation of FSH.$\text{In vitro}$ studies with these and other (frog, turtle, mammalian) gonadotropins indicate that the induction of ovulation in $\text{Ambystoma}$, as in anurans, is highly specific for LH, independent of the source of the gonadotropins. These data support the view that two separate gonadotropins existed early in tetrapod evolution.