Depletion of vitamin C from pig corpora lutea by prostaglandin F2 alpha-induced secretion of the vitamin

Abstract

The luteolytic effects of prostaglandin F2 alpha (PGF2 alpha) are thought to be mediated in part by the promotion of an increasingly oxidative cellular environment. Loss of antioxidants is one mechanism by which PGF2 alpha might induce or exacerbate oxidative damage within the corpus luteum. This study was performed to establish whether depletion of vitamin C is an acute effect of PGF2 alpha on the pig corpus luteum and to gain insight into the mechanism of luteal vitamin C loss at luteolysis. Gilts (n = 4) were anaesthetized and both utero-ovarian veins and an ear vein were catheterized. Each corpus luteum on the treated ovary received an intraluteal injection of PGF2 alpha (1 microgram) followed by a sustained release implant containing 100 micrograms of the prostaglandin. The other ovary served as the control and each corpus luteum received corresponding volumes of injection vehicle and blank implant. Blood was collected from the ear vein and both utero-ovarian veins every 15 min beginning 15 min before the onset of treatment. Collection of blood stopped when animals were ovariectomized and corpora lutea were collected at 2 h after treatment. Progesterone and vitamin C (ascorbate) concentrations were measured in tissue and plasma samples. PGF2 alpha-treated luteal tissue had similar progesterone, but significantly lower ascorbate, concentrations when compared with control corpora lutea. PGF2 alpha treatment resulted in a rapid and sustained increase in plasma ascorbate within the treatment-side utero-ovarian vein, while the control utero-ovarian vein and ear vein showed little change in plasma ascorbate during the experimental period. No effect of PGF2 alpha on plasma progesterone was evident. This finding suggests that PGF2 alpha depletes the pig corpus luteum of vitamin C by inducing secretion of the vitamin into the bloodstream. Further studies are necessary to determine whether the depletion of vitamin C that is induced by PGF2 alpha contributes to the demise of the pig corpus luteum.