Dexamethasone-induced changes in endometrial growth and inducible nitric oxide synthase: During decidualization in rats

1. The present study investigated the time-dependent inhibitory responses of endometrial growth and inducible nitric oxide synthase (iNOS) to dexamethasone during deciduoma development that was surgically induced on day 4 of pseudopregnancy (PG). 2. Groups of rats (n = 6) were subcutaneously injected with dexamethasone (1.5 mg/rat per day) for 3 days (PG days 1-3, 4-6, 7-9, 10-12 and 12-15), Rats in each group were killed on the last injection day, 3. Dexamethasone produced comparable temporal inhibitory changes in endometrial growth (wet weight, protein and DNA concentrations; P<0.0001) and in iNOS activity (130 kDa protein band), which peaked after PG days 4-6 and 7-9 pretreatments. 4. Endometrial matrix metalloproteinases (72 and 92 kDa) activity profiles displayed maximal reductions (36 and 53%, respectively) following PG days 4-6 pretreatment, Serum progesterone levels were equally (P<0.0001) but asynchronously inhibited by dexamethasone on PG days 9 and 12, 5. Dexamethasone inhibition of endometrial growth and in situ iNOS was most pronounced during decidual development (PG days 4-9), Minor reductions in these endometrial parameters occurred before deciduoma induction (PG days 1-3) and during deciduoma regression (PG days 10-15), 6. These results indicate that, in the endometrium, the iNOS/endogenous nitric oxide system may be linked to the biochemical and metabolic mechanisms responsible for the developmental responsiveness of the deciduoma to dexamethasone exposure, These time-dependent changes in endometrial growth and iNOS apparently were not mediated by progesterone.