Corpus luteum susceptibility to prostaglandin F2 alpha (PGF2 alpha) luteolysis in hysterectomized prepuberal and mature gilts.

The susceptibility of induced corpora lutea (CL) of prepuberal gilts and spontaneously formed CL of mature gilts to prostaglandin F2 alpha (PGF2 alpha) luteolysis was studied. Prepuberal gilts (120 to 130 days of age) were induced to ovulate with Pregnant Mare Serum Gonadotropin and Human Chorionic Gonadotropin (HCG). The day following HCG was designated as Day 0. Mature gilts which had displayed two or more estrous cycles of 18 to 22 days were used (onset of estrus = Day 0). Gilts were laparotomized on Day 6 to 9, their CL marked with sterile charcoal and totally hysterectomized. On Day 20, gilts were injected IM with either distilled water (DW), 2.5 mg PGF2 alpha or 5.0 mg PGF2 alpha. An additional group of prepuberal gilts was injected with 1.25 mg PGF2 alpha, a dose of PGF2 alpha equivalent, on a per kilogram body weight basis, to the 2.5 mg PGF2 alpha dose given to the mature gilts. The percentages of luteal regression on Day 27 to 30 for mature and prepuberal gilts given DW, 2.5 mg PGF2 alpha and 5.0 mg PGF2 alpha were 0.0 vs 4.4, 43.5 vs 96.8 and 47.7 vs 91.6, respectively; the percentage of luteal regression for the prepuberal gilts given 1.25 mg PGF2 alpha was 75.1. These results indicate that induced CL of the prepuberal gilt were more susceptible to PGF2 alpha luteolysis than spontaneously formed CL of the mature gilt and that pregnancy failure in the prepuberal gilt could be due to increased susceptibility of induced CL to the natural luteolysin.