Ms. Wisel et al., EFFECTS OF ANTIESTROGENS ON EARLY-PREGNANCY IN GUINEA-PIGS, International journal of fertility and menopausal studies, 39(3), 1994, pp. 156-163
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.