DIFFERENTIAL-EFFECTS OF 5-ALPHA-NORETHISTERONE ON THE HISTOMORPHOLOGYOF THE OVIDUCT AND UTERUS OF THE PREGNANT RABBIT

In this study, the histomorphological changes induced by 5 alpha-noret histerone (5 alpha-NET), a reduced metabolite of the contragestational postcoital agent norethisterone, in the oviduct and the uterus of the pregnant rabbit were determined. Adult fertilized rabbits were treate d daily with 5 alpha-NET (1.0, 1.5, 2.5, and 5.0 mg/kg/day) during 7 c onsecutive days, starting from the first day after coitus. Twenty-four hours after the last administration, the histological analysis of the oviduct and the uterus was performed. It was observed that in the inf undibulum-ampullae region as well as in the isthmus of the oviduct, th e number of nonsecretory cells (PAS-negative) were decreased. whereas the number of secretory cells (PAS-positive) were increased significan tly after 5 alpha-NET administration. The proportion of glandular tiss ue in the uterus markedly diminished in relation to that of the stroma l tissue. This indicates an inhibition of the endometrial transformati on observed during normal pregnancy. Interestingly, the highest doses of 5 alpha-NET (2.5 and 5.0 mg/kg/day) induced necrosis in the uterus but not in the oviduct. These results suggest that the molecular antip rogestational effects previously observed alter 5a-NET administration are also related to changes in the histomorphology of both the oviduct and the uterus of the pregnant rabbit. CONTRACEPTION 1998;57:349-355 (C) 1998 Elsevier Science Inc. All rights reserved.