In vivo responses of female snakes (Natrix fasciata) and female turtles (Chrysemys picta) to ovine gonadotropins (FSH and LH) as measured by plasma progesterone, testosterone, and estradiol levels.

Abstract

Changes in plasma progesterone, testosterone, and estradiol-17β in serially bled female snakes (Natrix fasciata) and female turtles (Chrysemys picta) in response to single iv injections of ovine LH or FSH were measured by RIA. In snakes, both FSH and LH increased the levels of all three steroids in plasma, though considerable individual variation in response to either hormone was encountered. The apparent differences in the responses to the gonadotropins may have been due to differences in the stage of follicular development in different animals. In contrast, in female turtles, ovine FSH was clearly most active in stimulating steroid (testosterone and estradiol) synthesis, although LH has a consistent, though minor, stimulatory effect on estradiol secretion 30 min after injection. Neither hormone stimulated progesterone secretion at the time of year tested. In snakes, but not in turtles, it was possible to correlate preinjection plasma levels of estradiol with the stage of follicular development, high levels of hormone being found in animals with large follicles and low levels in animals with small follicles.