DEPLETION OF VITAMIN-C FROM PIG CORPORA-LUTEA BY PROSTAGLANDIN F-2-ALPHA-INDUCED SECRETION OF THE VITAMIN

The luteolytic effects of prostaglandin F-2 alpha (PGF(2 alpha)) are t hought to be mediated in part by the promotion of an increasingly oxid ative cellular environment. Loss of antioxidants is one mechanism by w hich PGF(2 alpha) might induce or exacerbate oxidative damage within t he corpus luteum. This study was performed to establish whether deplet ion of vitamin C is an acute effect of PGF(2 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-ovaria n veins and an ear vein were catheterized. Each corpus luteum on the t reated ovary received an intraluteal injection of PGF(2 alpha) (1 mu g ) followed by a sustained release implant containing 100 mu g of the p rostaglandin. The other ovary served as the control and each corpus lu teum received corresponding volumes of injection vehicle and blank imp lant. Blood was collected from the ear vein and both utero-ovarian vei ns every 15 min beginning 15 min before the onset of treatment. Collec tion of blood stopped when animals were ovariectomized and corpora lut ea were collected at 2 h after treatment. Progesterone and vitamin C ( ascorbate) concentrations were measured in tissue and plasma samples. PGF(2 alpha)-treated luteal tissue had similar progesterone, but signi ficantly lower ascorbate, concentrations when compared with control co rpora lutea. PGF(2 alpha) treatment resulted in a rapid and sustained increase in plasma ascorbate within the treatment-side utero-ovarian v ein, while the control utero-ovarian vein and ear vein showed little c hange in plasma ascorbate during the experimental period. No effect of PGF(2 alpha) on plasma progesterone was evident. This finding suggest s that PGF(2 alpha) depletes the pig corpus luteum of vitamin C by ind ucing secretion of the vitamin into the bloodstream. Further studies a re necessary to determine whether the depletion of vitamin C that is i nduced by PGF(2 alpha) contributes to the demise of the pig corpus lut eum.