Physiologic and nonphysiologic effects of exogenous prostaglandin F2alpha on reproductive hormones in mares.
Responses to intravenous treatment of mares with prostaglandin F2alpha (PGF) 8 d after ovulation were studied in three groups (n=4/group): control (no treatment), bolus (single treatment with 2.5 mg PGF), and infusion (0.1 mg PGF during 2 h). Infusion resulted in a 13,14-dihydro-15-keto-PGF2alpha (PGFM) concentration (559+/-44 pg/mL) that was not different from the mean concentration for the major portion of a natural PGFM pulse associated with luteolysis (569+/-45 pg/mL; n=5). Progesterone in the bolus group increased (P<0.03) between 0 (17.8+/-3.5 ng/mL) and 2 min (25.3+/-4.8 ng/mL), peaked at 10 min (28.5+/-4.6 ng/mL), and then decreased. In the infusion group, progesterone decreased (P<0.05) during 1 min (17.2+/-1.3 ng/mL) to 15 min (13.5+/-1.5 ng/mL) after the beginning of infusion and decreased (P<0.05) similarly to the bolus group during 2 to 12 h; concentrations were lower (P<0.05) at each hour than in controls. Interval between ovulations was shorter (P<0.05) in the bolus (19.3+/-2.0 d) and infusion (18.8+/-2.1 d) groups than in controls (24.3+/-1.3 d). Concentrations of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and cortisol increased (P<0.05) within 10 min in the bolus group but did not change in the infusion group. Results supported the hypothesis that increases in progesterone, FSH, LH, and cortisol after a bolus luteolytic PGF treatment are nonphysiologic. Past conclusions on the nature of the luteolytic mechanism are problematic if based on responses to treatment with a single luteolytic bolus of PGF.
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
Siddiqui
M A R
MA
Beg
M A
MA
D000818:Animals; D015237:Dinoprost / Q000008:administration & dosage / Q000031:analogs & derivatives / Q000097:blood* / Q000378:metabolism / Q000494:pharmacology*; D030762:Estrous Cycle / Q000097:blood / Q000187:drug effects / Q000378:metabolism; D012739:Gonadal Steroid Hormones / Q000097:blood*; D006736:Horses / Q000097:blood / Q000502:physiology*; D006854:Hydrocortisone / Q000097:blood; D007262:Infusions, Intravenous; D013997:Time Factors
D012739:Gonadal Steroid Hormones; C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D015237:Dinoprost; D006854:Hydrocortisone