Effects of luteinizing hormone, progesterone, testosterone, estradiol and corticosterone on ovulation and luteinizing hormone release in hens treated with aminoglutethimide.
Aminoglutethimide (AG), an inhibitor of steroidogenesis, was administered s.c. to 5 groups of laying hens at a dose of 200 mg AG/kg body weight 9 h before expected midsequence ovulation. This dose has previously been demonstrated to consistently block ovulation. The injection of AG was followed by s.c. injections of: Group 1, 1.0 mg progesterone; Group 2, 0.1 mg estradiol-17 beta; Group 3, 1.5 mg corticosterone, all at 6 h prior to expected ovulation; Group 4, 1.0 mg testosterone at both 8 h and 5 h before expected ovulation; and Group 5, 25 micrograms of ovine luteinizing hormone (LH) at 8 and 50 micrograms ovine LH at 6 h before expected ovulation. For each group, 4 control hens were injected with AG and the appropriate vehicle. Blood samples were taken at 1- or 2-h intervals from the time of AG injection to the expected time of ovulation. The hens were killed 4 h after expected ovulation and examined for the occurrence of ovulation. In all hens injected with vehicle, ovulation and the preovulatory surges of progesterone, testosterone, estradiol-17 beta and LH were inhibited. The plasma concentration of corticosterone was not reduced following an injection of AG. Four of 6 hens ovulated in response to injection of ovine LH, although neither endogenous LH nor progesterone were released. Thus, LH appears to play a direct role in follicular rupture and extrusion of the ovum. The administration of progesterone induced a significant and prolonged rise in LH, restoring AG-blocked ovulation in all hens treated (n = 6). Injections of testosterone restored LH release in all hens and ovulation in 2 of 7 hens treated. Three of 7 hens ovulated in response to the corticosterone injection. A preovulatory rise in LH was not observed, indicating that corticosterone may exert its ovulation-inducing effect directly on the mature follicle. Estradiol-17 beta did not restore LH release or ovulation in any of the hens treated with AG.
D000616:Aminoglutethimide / Q000494:pharmacology*; D000818:Animals; D002645:Chickens; D003345:Corticosterone / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D005260:Female; D006728:Hormones / Q000494:pharmacology*; D007986:Luteinizing Hormone / Q000378:metabolism* / Q000494:pharmacology; D010060:Ovulation / Q000187:drug effects*; D011374:Progesterone / Q000494:pharmacology; D013256:Steroids / Q000096:biosynthesis; D013739:Testosterone / Q000494:pharmacology
D006728:Hormones; D013256:Steroids; D000616:Aminoglutethimide; D013739:Testosterone; D011374:Progesterone; D004958:Estradiol; D007986:Luteinizing Hormone; D003345:Corticosterone