PARENT SESSION
SLIDE SESSION 10: MECHANISMS OF LUTEAL REGRESSION
Chairs: Bo Rueda, Jack Carlson, Carlos Stocco (Trainee)
Arts Hall 026
1:30 PM-3:30 PM

PROSTAGLANDIN F₂-INDUCED EXPRESSION OF PROSTAGLANDIN SYNTHASE (PGHS) AND DISRUPTION OF PROGESTERONE PRODUCTION BY INHIBITORS OF PGHS IN THE RAT CORPUS LUTEUM .

Narayansingh, Richard¹, Nykamp, Julie¹, Senchyna, Michelle², Kyveris, Angela², Bols, Niels¹, Carlson, Jack¹, ^{1 2}

ABSTRACT- PGF2 causes luteolysis in the rat ovary. The enzyme PGHS plays a key role in producing PGs from arachidonic acid. In the present study, we examined expression of PGHS mRNA in the CL of pseudopregnant rats. Immature animals were superovulated and treated with a luteolytic dose of PGF2 on day 9 of pseudopregnancy. Ovaries and serial blood samples were removed during the 24-hour period following treatment. The ovaries were homogenized, total RNA was isolated, and levels of mRNA for PGHS-1 (constitutive), PGHS-2 (inducible) and glyceraldehyde-3-phosphate dehydrogenase (GAPDH, internal control) were estimated by semi-quantitative RT PCR. The results of three experiments indicate that there was an increase in mRNA for PGHS-2 one hour after PGF2 injection. Levels of this transcript, however, were lower at 8 and 24 hours. In addition, there was no change in the level of expression of mRNA for PGHS-1 or GAPDH over the collection period. Immunoblot analysis, using a polyclonal antibody for the induced isoform, indicated an increase in PGHS-2 protein in samples removed 8 hours after PGF2 injection. Radioimmunoassay of blood samples confirmed that PG treatment decreased production of progesterone at one hour. In this study we also examined whether PGHS may be involved in luteinizing hormone (LH) stimulation of progesterone production. When suspensions of CL cells prepared from superovulated rats on day 4 of pseudopregnancy were treated with indomethacin (10 and 100 ng/10⁵ cells), an inhibitor of PGHS, LH (10 ng) stimulated progesterone production was reduced approximately 50%. Interestingly, addition of 1 microgram of NS398, a PGHS inhibitor reported to be selective for PGHS-2, also decreased LH stimulated progesterone secretion. These results demonstrate that PGF2a treatment stimulates expression of PGHS-2 in the rat ovary during CL regression and that PGHS may also be involved in the mechanism by which LH stimulates production of progesterone.

KEY WORDS: prostaglandin f2a, prostaglandin synthase constitutive and induced, reverse transcriptase polymerase chain reaction, prostaglandin synthase inhibitors