Gonadotropin stimulation of in vitro progesterone production in reptilian and amphibian ovaries

Abstract

The gonadotropic stimulation of progesterone production in vitro by preovulatory ovarian tissues from a chelonian reptile ( Chelydra serpentina), crocodilian ( Caiman sclerops), urodele amphibian ( Ambystoma tigrinum) and anuran amphibian ( Rana catesbeiana) was examined with a variety of mammalian and nonmammalian hormones, with emphasis on the homologous FSH and LH. In the turtle ovary, ovine (NIH) FSH was the most potent hormone while NIH-LH was relatively inactive. However, both FSH and LH from a turtle ( Chelonia mydas) and crocodilian ( Alligator mississipiensis) were effective; the two reptilian LHs appeared more potent than the FSHs. Similarly, both FSH and LH from the alligator and sheep effectively stimulated progesterone production by the Caiman ovary; in this case, Alligator-LH was the most potent steroidogenically. Results with postovulatory follicles and corpora lutea from the snapping turtle ( Chelydra) were similar to those for preovulatory tissues. FSH from sheep and Chelydra were more potent than the respective LHs. Ovine LH was especially inactive in these tissues, but the homologous LH stimulated significant progesterone production. In contrast, only LH (ovine and amphibian were tested) stimulated progesterone release from the two amphibian ovaries. Rana-LH was more potent than ovine LH in Rana. In Ambystoma, both progesterone secretion and ovulation were observed over a wide range of doses of homologous LH, but FSH was inactive in both regards. Ovulation was inhibited while progesterone was maximal at the highest doses of LH. These comparative data suggest that the “primitive” tetrapod condition involved a relatively high specificity for LH for the control of ovarian progesterone production. This LH-specificity was apparently lost during early reptilian radiation, at least by the time that the captorhinids diverged into the extant orders. Since FSHs from diverse species are active in reptiles (and reptilian LHs but not FSHs are active in amphibians), the sensitivity to FSH in the reptilian ovary is viewed as being due to an alteration in gonadal receptors rather than to a structural change in the reptilian FSH molecule.