Relation between biological potency and clearance rates of gonadotropins in the lizard Anolis carolinensis

Abstract

Clearance of exogenous gonadotropins was studied in the lizard Anolis carolinensis in relation to the problem of variations in potency ratios between LH and FSH of different species of hormone. Studies with unlabeled bullfrog (Rana catesbeiana) gonadotropins revealed that the FSH had a much longer persistence time in the lizard than did LH; this was confirmed by direct immunological measurements of circulating hormone and by temporal profiles in the stimulation of gonadal androgen production in the lizard. Bullfrog FSH and LH labeled with 125I had similar clearance rates; the clearance of (125I) Rana LH was slower than that of the unlabeled preparation. In contrast, similar studies with unlabeled sea turtle (Chelonia mydas) hormones indicated that the LH is cleared more slowly than is FSH. These differences between the pairs of frog and turtle gonadotropins are consistent with the difference in LH/FSH potency ratios observed for the two species of hormone in the in vivo Anolis lizard testes weight bioassay. Thus, these data provide additional insights into the variability in effects of different species of gonadotropins: the relatively high potency of some species of LH may be related in part to increased half-lives.