Participation of ovarian 20α-hydroxysteroid dehydrogenase in luteotrophic and luteolytic processes during rat pseudopregnancy

In normal rats, before Day 12 of pseudopregnancy, minimal levels of 20α-HSD activity were detected in functional CL whereas those in the residue were 3-5 times higher. When ovulation was blocked for more than 2 weeks by placing rats in a continuously lit environment before the induction of pseudopregnancy, only minimal levels of 20α-HSD activity were detectable in the functional CL and residue before Day 12. In normal pseudopregnant rats, there was a linear increase in 20α-HSD activity from Day 12 to 15 in the functional CL and residue, but the rate of elevation was much higher in functional CL. This tendency was much more clear-cut in rats in the continuous lighting. In immature rats in which pseudopregnancy was induced by PMSG and hCG treatment, 20α-HSD activity peaked twice. The first small peak was attributed to the early regression of some of the large number of corpora lutea, and the changes in 20α-HSD activity in most of the corpora lutea paralleled those in rats in continuous lighting. Bromocriptine abolished the prolactin surges, and in normal pseudopregnant rats an increase in 20α-HSD activity in functional CL started from 12 h and the rate of the increase was accelerated from 36 h afterwards, while a relatively small increase was observed in the residue at 18 h and later. These results suggest that, in the early-middle phase of pseudopregnancy, 20α-HSD activity in the functional CL is suppressed under the control of prolactin and at the end of pseudopregnancy 20α-HSD activity appears mainly in the functional CL without suppressive action of prolactin.