The specific activity of NAD(+)-dependent 15-hydroxyprostaglandin dehydrogenase (PGDH) was found to increase in the ovaries of pregnant and pseudopregnant rabbits. The mean specific activity of cytosolic ovarian PGDH in 14- to 28-day pregnant rabbits was 24.3 +/- 8.1 nmol NADH formed/min/mg protein (n = 16) using PGE1 as substrate whereas in nonpregnant rabbits the specific activity was 1.5 +/- 0.8 nmol NADH formed/min/mg protein (n = 8). The reaction was dependent on NAD+; NADP+ did not support the reaction. In grouping the PGDH activities from pregnant rabbits into second (14-18 days) and third (2-28 days) trimester periods, no significant difference between values was found (26.1 +/- 8.9 vs 23.4 +/- 8.1 nmol NADH formed/min/mg protein, respectively). Western blot analysis of the ovarian cytosol using an antibody which was made to the purified lung PGDH of pregnant rabbits recognized an ovarian protein of identical molecular mass (30 kDa). Ovarian PGDH activities were also examined in rabbits treated with pregnant mare's serum gonadotrophin (PMSG) and human chorionic gonadotrophin (hCG) to induce a state of superovulatory/pseudopregnancy and only on day 11 following hCG treatment was an increase in PGDH specific activity observed. On day 11, the specific activity was 14.8 +/- 4.3 nmol NADH formed/min/mg protein whereas values on days 10 and 12 were only 1.1 +/- 1.1 and 1.0 +/- 0.8, respectively. PGDH activities on days 3, 7 and 16 were also low.(ABSTRACT TRUNCATED AT 250 WORDS)