Ovarian 3 beta-hydroxysteroid dehydrogenase and sulfated glycoprotein-2 gene expression are differentially regulated by the induction of ovulation, pseudopregnancy, and luteolysis in the immature rat.

The present studies were conducted to elucidate the effects of gonadotropin-induced alterations in ovarian status on expression of 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD), an enzyme which plays a crucial role in steroidogenesis, and sulfated glycoprotein-2 (SGP-2), a heterodimeric protein which is highly expressed by cells undergoing programmed death (i.e. apoptosis). Prepubescent female rats were used to reduce the influence of endogenous gonadotropins and to avoid the presence of preexisting, degenerating corpora lutea in the ovaries. 3 beta-HSD, cholesterol side-chain cleavage cytochrome P450, and SGP-2 messenger RNA (mRNA) levels were measured by Northern analysis of total ovarian RNA. Rats which received PMSG (20 IU) followed 48 h later by human CG (hCG) (10 IU) to induce ovulation and pseudopregnancy exhibited a significant increase in ovarian 3 beta-HSD mRNA 1 day later (164%, P less than 0.01 vs. saline control). The most dramatic change in 3 beta-HSD expression was the rise seen 2 days after hCG (262%, P less than 0.01), after which levels remain constantly elevated throughout pseudopregnancy. In contrast, ovarian cholesterol side-chain cleavage cytochrome P450 mRNA was greatly elevated (i.e. 15-fold) 48 h after PMSG treatment alone (P less than 0.01). Thus, gonadotropic stimulation which induces ovulation and luteogenesis is required to observe a potent stimulatory effect on ovarian 3 beta-HSD expression. The slow time course of induction is indicative of a differentiation-dependent expression. These observations are consistent with luteal cell expression of the 3 beta-HSD gene and suggest that this expression is correlated with the high progestin secretion and 3 beta-HSD activity characteristic of luteal cells. Interestingly, the pattern of regulation of ovarian SGP-2 expression was markedly different than that observed for 3 beta-HSD. PMSG treatment alone (48 h), and in combination with hCG, dramatically reduced SGP-2 mRNA to 12-27% of controls (P less than 0.01). SGP-2 levels were not elevated until 7 days after hCG; levels then remained constant through day 14 of pseudopregnancy. Since luteal progesterone secretion begins to diminish 5-7 days after hCG, the increased expression of SGP-2 on day 7 may be related to the initiation of the regression/degeneration of luteal cells which occurs during luteolysis. Thus, this study demonstrates that alterations in SGP-2 expression by the ovary may precede or occur simultaneously with cellular events initiating luteolysis and suggests a role for this glycoprotein as an early marker for luteolysis and implicates it in yet another instance of programmed cell death.