Relation between acute pituitary responsiveness to gonadotropin releasing hormone (GnRH) and the ovarian cycle in the bullfrog, Rana catesbeiana.
Freshly captured female bullfrogs (Rana catesbeiana) were challenged with a standard dose (2 micrograms) of gonadotropin-releasing hormone (GnRH) shortly before and at the onset of the spawning season (in early April and mid-May) to examine the relationship between pituitary responsiveness and ovarian stage; males were also tested in April. As shown previously, increments in plasma gonadotropins induced by GnRH were consistently lower in females than in males. There was little difference in average responsiveness between the two collections of females and results for these were similar to those obtained at other times of the year. A wide range of ovarian stages was represented at both collection times as evidence by plasma steroid profiles, but there was no correlation between the GnRH-induced increments in plasma FSH and LH and plasma levels of androgens (testosterone and 5 alpha-dihydrotestosterone), estradiol-17 beta, or progesterone in the 71 females tested. Thus, there is no evidence of a feedback effect of ovarian steroids on the pituitary responsiveness to acute GnRH stimulation in the frog as has been demonstrated in mammals.
D000818:Animals; D005260:Female; D005640:Follicle Stimulating Hormone / Q000097:blood; D007987:Gonadotropin-Releasing Hormone / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000097:blood; D008297:Male; D010053:Ovary / Q000502:physiology*; D010902:Pituitary Gland / Q000187:drug effects*; D011892:Rana catesbeiana; D012621:Seasons
D007987:Gonadotropin-Releasing Hormone; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone