CIRCADIAN MODIFICATION OF UTERINE RESPONSES BY DAY-NIGHT DEXAMETHASONE TREATMENT DURING DECIDUALIZATION IN RATS

The effect of treatment (1 mg/rat for 5 days, post-implantation) with the synthetic glucocorticoid, dexamethasone (Dex) on the biochemical c omponents in uterine proliferation during decidualization in rats was assessed. Dex was administered subcutaneously either at only one time (two hours after lights off) of the scotophase, or again at one time ( two hours after lights on) during the photophase of a fixed 24 hours ( 12L: 12D) photoperiod. The uterine parameters included the wet weight, protein and DNA concentrations, nuclear estrogen receptors, enzymatic activities of alkaline phosphatase, isocitrate dehydrogenase and the matrix metalloproteinases, and serum levels of estradiol and progester one. Certainly the rat circadian system, under the influence of the hy pothalamic suprachiasmatic nucleus is fully entrained by the alternati on of the experiment. Hence, the results suggest that between the two injections times, there may be a circadian difference in the uterine r esponses to Dex. The findings have meaningful implications for Dex and the optimal effectiveness of its application times for implantation p roblems.