EFFECTS OF ANTIESTROGENS ON EARLY-PREGNANCY IN GUINEA-PIGS

Objective-To compare effects of various anti-estrogens on early pregna ncy. Methods-Fifty regularly cycling guinea pigs were divided into fiv e groups (five animals/group), of which three groups received 3 mg/kg body weight Nafoxidine, Centchroman, or Tamoxifen, respectively, on th e 1st, 2nd, or 3rd day of pregnancy. The rest of the animals were kept as controls, and received either saline or propylene glycol. Autopsie s were done on the 8th day of pregnancy in all the groups. Presence or absence of implantation sites was observed by using a stereomicroscop e. Plasma levels of 17 beta-estradiol and progesterone and their recep tors, as well as enzyme levels in the uterine tissue, were estimated. Results-During normal early pregnancy there was an increase in the con centration of peripheral plasma levels of steroid hormones with respec t to enzyme and steroid hormone receptor levels in the uterus. Adminis tration of anti-estrogens showed a decreased trend in all the variable s studied, especially in the tamoxifen-treated animals. Conclusions-Th e results of the study suggest that anti-estrogens, if administered du ring early pregnancy, can prevent the process of ovum implantation in this species.