Disruption of the periovulatory LH surge by a transient increase in circulating 17beta-estradiol at the time of ovulation in mares.
The mechanism for a reported temporal association between ovulation and a transient disruption in the periovulatory increase in LH concentrations was studied in nine mares treated with human chorionic gonadotropin when the preovulatory follicle was >/=32mm. Examinations for ovulation detection and blood collection were done at 2-h intervals and the results were retrospectively centralized to ovulation (Hour 0). Concentrations of LH began to increase (P<0.03) rapidly at Hour -18, decreased (P<0.04) between Hours 0 and 6, and again increased (P<0.0001) after Hour 12. A progressive decrease (P<0.0001) in estradiol between Hours -30 and 24 was interrupted temporarily by an increase (P<0.01) between Hours -2 and 0 and a decrease (P<0.007) between Hours 0 and 2. Results indicated that a disruption and depression in the periovulatory LH surge occurred at the time of detected ovulation in mares and was temporally associated with a transient increase in estradiol during an overall progressive decline. The disruption in LH concentrations is attributable to the estradiol increase, based on a reported negative effect of estradiol on LH. The source of the circulating estradiol was likely from the discharge of estradiol-laden follicular fluid into the abdomen during ovulation and rapid absorption of estradiol into the circulation.
Ginther
O J
OJ
Eutheria Foundation, Cross Plains, WI 53528, USA; Pathobiological Sciences, University of Wisconsin, Madison, WI 53706, USA. ginther@svm.vetmed.wisc.edu
Almamun
M
M
Shahiduzzaman
A K M
AK
Beg
M A
MA
D000818:Animals; D006063:Chorionic Gonadotropin / Q000008:administration & dosage; D004958:Estradiol / Q000097:blood* / Q000378:metabolism; D005260:Female; D015571:Follicular Fluid / Q000737:chemistry / Q000378:metabolism; D006736:Horses / Q000097:blood*; D007700:Kinetics; D007986:Luteinizing Hormone / Q000097:blood*; D010060:Ovulation / Q000097:blood*; D010061:Ovulation Detection / Q000662:veterinary; D010062:Ovulation Induction / Q000662:veterinary
D006063:Chorionic Gonadotropin; D004958:Estradiol; D007986:Luteinizing Hormone