title: Regression and resurgence of the CL following PGF2alpha treatment 3 days after ovulation in mares.
abstract: The present study was designed to characterize and compare the physiology and ultrasonographic morphology of the corpus luteum (CL) during regression and resurgence following a single dose of native prostaglandin F2alpha (PGF) given 3 days after ovulation, with a more conventional treatment given 10 days after ovulation. On the day of pre-treatment ovulation (Day 0), horse mares were randomly assigned to receive PGF (Lutalyse; 10 mg/mare, i.m.) on Day 3 (17 mares) or Day 10 (17 mares). Beginning on either Days 3 or 10, follicle and CL data and blood samples were collected daily until post-treatment ovulation. Functional and structural regression of the CL in response to PGF treatment were similar in both the Day 3 and 10 groups, as indicated by an abrupt decrease in circulating concentrations of progesterone, decrease in luteal gland diameter and increase in luteal tissue echogenicity. As a result, the mean +/- S.E.M. interovulatory interval was shorter (P < 0.0001) in the Day 3 group (13.2 +/- 0.9 days) than in the Day 10 group (19.2 +/- 0.7 days). Within the Day 3 group, functional resurgence of the CL was detected in 75% of the mares (12 of 16) beginning 3 days after PGF treatment, as indicated by transient major (6 mares) and minor (6 mares) increases (P < 0.05 and < 0.1, respectively) in progesterone. Correspondingly, mean length of the interovulatory interval was longer (P < 0.03) in mares with major resurgence (15.8 +/- 1.6 days) than in mares with minor (11.2 +/- 1.2 days) and no resurgences (13.5 +/- 0.3 days) in progesterone. Structural resurgence of the CL in the Day 3 group and functional and structural resurgence in the Day 10 group were not detected. In conclusion, PGF treatment 3 days after ovulation resulted in structural and functional regression of the CL and hastened the interval to the next ovulation, despite post-treatment resurgences in progesterone.
authors.affiliation: Department of Animal Health and Biomedical Sciences, University of Wisconsin, Madison, WI 53706, USA. bergfelt@svm.vetmed.wisc.edu
authors.forename: D R
authors.initials: DR
authors.lastname: Bergfelt
authors.forename: R A
authors.initials: RA
authors.lastname: Pierson
authors.forename: O J
authors.initials: OJ
authors.lastname: Ginther
mesh_terms: D000818:Animals; D003338:Corpus Luteum / Q000000981:diagnostic imaging / Q000187:drug effects* / Q000502:physiology; D015237:Dinoprost / Q000494:pharmacology*; D005260:Female; D006736:Horses / Q000502:physiology*; D006080:Ovarian Follicle / Q000033:anatomy & histology / Q000187:drug effects; D010060:Ovulation / Q000502:physiology*; D011374:Progesterone / Q000097:blood*; D011897:Random Allocation; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D011374:Progesterone; D015237:Dinoprost