Abstract
Since the regression of the corpus luteum (CL) occurs via a tightly controlled apoptotic process, studies were designed to determine if local administration of the antiapoptotic agent sphingosine 1-phosphate (S1P) effectively blocks the luteolytic action of prostaglandin F-2alpha (PGF-2alpha). On day 19 of pregnancy, 2 hr before systemic PGF-2alpha administration, rats were injected intrabursa with either S1P or vehicle (control). The activity of four caspases, which contribute to the initial (caspase-2, -8, and -9) and final (caspase-3) events in apoptosis was measured in pooled CL from four individual ovaries at 0 and 4 hr after PGF-2alpha injection. The expression of the phosphorylated form of AKT (pAKT) and tumor necrosis factor-alpha (TNF-alpha) was analyzed by ELISA. In addition, cell death was evaluated by electronic microscopy (EM) in CL 4 and 36 hr after PGF-2alpha injection. The activity of caspase-2, -3, and -8 was significantly greater by 4 hr after PGF-2alpha, but not caspase-9 activity. In contrast, expression of pAKT and TNF-alpha decreased significantly. Administration of S1P suppressed (P < 0.05) these effects, decreasing caspase activities and increasing pAKT and TNF-alpha expression. The administration of S1P also significantly decreased the percentage of luteal apoptotic cells induced by PGF-2alpha. PGF-2alpha treatment increased the prevalence of luteal cells with advanced signs of apoptosis (i.e., multiple nuclear fragments, chromatin condensation, or apoptotic bodies). S1P treatment suppressed these changes and increased the blood vessel density. These results suggest that S1P blocks the luteolytic effect of the PGF-2alpha by decreasing caspase-2, -3, and -8 activities and increasing AKT phosphorylation and TNF-alpha expression.