Priming with progestin, but not GnRH antagonist, induces a consistent endocrine response to exogenous gonadotropins in induced and spontaneously ovulating cats

• Published in: Domestic animal endocrinology Vol. 34; no. 2; pp. 160 - 175
• Main Authors: Pelican, Katharine M., Wildt, David E., Ottinger, Mary A., Howard, JoGayle
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 01-02-2008; [Amsterdam; New York]: Elsevier Science Pub. Co
• Subjects: Animals; antide; cats; Cats - physiology; Chorionic Gonadotropin - pharmacology; equine chorionic gonadotropin; estradiol; Estradiol - metabolism; Estrous Cycle - drug effects; Estrous Cycle - physiology; Fecal steroids; Feces - chemistry; Female; gonadotropin stimulation; Gonadotropin-releasing hormone; Gonadotropin-Releasing Hormone - antagonists & inhibitors; hormonal regulation; hormone antagonists; Hormone Antagonists - pharmacology; hormone pretreatment; hormone secretion; human chorionic gonadotropin; induced ovulation; levonorgestrel; Levonorgestrel - pharmacology; Oligopeptides - pharmacology; ovarian inhibition; ovaries; Ovary; Ovulation; Ovulation - drug effects; Ovulation - physiology; Progesterone; Progesterone - metabolism; Radioimmunoassay - veterinary; Random Allocation; Reproductive Techniques, Assisted - veterinary; spontaneous ovulation; synthetic progestogens; Fecal steroids; Ovary; Gonadotropin-releasing hormone; Progesterone; Ovulation
• ISSN: 0739-7240; 1879-0054
• DOI: 10.1016/j.domaniend.2007.01.002

Ovarian sensitivity to exogenous gonadotropin stimulation (equine chorionic gonadotropin [eCG] and human chorionic gonadotropin [hCG]) following pre-treatment with a progestin (levonorgestrel) versus GnRH antagonist (antide) was studied in cats known to be induced versus spontaneous ovulators. Queens were assigned to one of three treatments: (1) levonorgestrel implants
+
eCG/hCG (
n
=
7 cats); (2) antide injections
+
eCG/hCG (
n
=
7) or (3) eCG/hCG alone (control;
n
=
7). Hormonal metabolites were assessed in fecal samples collected daily for 60 days before and during the 37 days inhibitory pre-treatment and for more than 60 days after eCG/hCG. Fecal metabolites of estradiol and progesterone were measured by radioimmunoassay. Females that maintained baseline progesterone were considered induced ovulators, whereas cats that exhibited a luteal phase before inhibition treatment were classified as spontaneous ovulators. Based on fecal hormone profiles, levonorgestrel thoroughly inhibited ovarian activity, whereas antide synchronized follicular phases but did not induce complete ovarian down-regulation. Both treatments prevented ovulation in spontaneous ovulators, but neither caused regression of existing corpora lutea (CL). Levonorgestrel, but not antide, pre-treatment resulted in a quiescent ovary at the time of eCG injection, yet endocrine responses to eCG/hCG were not different among treatments. Interestingly, spontaneously ovulating females exhibited a prolonged estradiol response to gonadotropin stimulation compared to induced ovulators, and this prolonged estradiol surge was replicated by levonorgestrel pre-treatment. Thus, the progestin levonorgestrel effectively suppresses follicular and luteal activity in the cat, resulting in a more consistent response to gonadotropin stimulation, even in females prone to spontaneous ovulation.