title: Effect of human chorionic gonadotropin on preovulatory luteinizing hormone surge and ovarian hormone secretion in gilts.
abstract: The influence of varying doses of human chorionic gonadotropin (hCG) on the preovulatory luteinizing hormone (LH) surge, estradiol-17 beta (E2) and progesterone (P4) was studied in synchronized gilts. Altrenogest (AT) was fed (15 mg X head-1 X d-1) to 24 cyclic gilts for 14 d. Pregnant mares serum gonadotropin (PMSG; 750 IU) was given im on the last day of AT feeding. The gilts were then assigned to one of four groups (n = 6): saline (I), 500 IU hCG (II), 1,000 IU hCG (III) and 1,500 IU hCG (IV). Human chorionic gonadotropin or saline was injected im 72 h after PMSG. No differences in ovulation rate or time from last feeding of AT to occurrence of estrus were observed. All gilts in Groups I and II expressed a preovulatory LH surge compared with only four of six and three of six in Groups III and IV, respectively. All groups treated with hCG showed a rapid drop (P less than .01) in plasma levels of E2 11, 17, 23 h after hCG injection when compared with the control group (35 h). The hCG-treated gilts exhibited elevated P4 concentrations 12 h earlier than the control group (3.1 +/- .5, 3.4 +/- .72, 3.1 +/- .10 ng/ml in groups II, III and IV at 60 h post-hCG vs .9 +/- .08 ng/ml in group I; P less than .05). These studies demonstrate that injections of ovulatory doses of hCG (500 to 1,500 IU) had three distinct effects on events concomitant with occurrence of estrus in gilts: decreased secretion of E2 immediately after hCG administration, failure to observe a preovulatory LH surge in some treated animals and earlier production of P4 by newly developed corpora lutea.
mesh_terms: D000818:Animals; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D004958:Estradiol / Q000378:metabolism*; D004973:Estrus Synchronization / Q000187:drug effects; D005260:Female; D006064:Gonadotropins, Equine / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000097:blood*; D011374:Progesterone / Q000378:metabolism*; D045167:Progesterone Congeners / Q000494:pharmacology; D013552:Swine / Q000502:physiology*; D014204:Trenbolone Acetate / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D006063:Chorionic Gonadotropin; D006064:Gonadotropins, Equine; D045167:Progesterone Congeners; C023445:altrenogest; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D014204:Trenbolone Acetate