EFFECT OF DEXAMETHASONE AS AN INHIBITOR OF IMPLANTATION AND EMBRYO DEVELOPMENT IN RAT - LYSOSOMAL ROLE

In order to learn the mechanism of action of dexamethasone administrat ion as an efficient inhibitor of estrogen activity in different tissue s, the subcellular enzymatic distribution of two lysosomal enzymes: ac id phosphatase (E.C.3.1.3.2.) and beta lucuronidase (E.C.3.2.1.3.1.) w ere measured. The rats were treated during preimplantation with dexame thasone (0.8 mg on days 3 and 4) or saline (controls). In the control group, the nuclear activity of lysosomal enzymes was significantly les s in the implantation site tissue than in the treated group (p < 0.05) . There were no modifications on the undecidualized endometrium under the steroid treatment. The lysosomal subfraction showed an opposite re sponse. The steroid treatment produced an increase of activity in the decidualized tissue (1.9 +/- 0.4 to 4.9 +/- 0.4) while the nuclear enz ymatic activity decreased under treatment; and simultaneously, the emb ryonic development was 100% abolished. From the results presented here in, it is proposed that the inhibitory effect of dexamethasone upon im plantation is due to an inadequate biochemical differentiation at the implantation site, related to the inhibition of lysosomal movement tow ard the nucleus, and consequently to lysosomal enzymatic release and m etabolic role.