Body weight and growth rates throughout the guinea pig pregnancy: evidence for modulation by endogenous estrogens.

Relationships between endocrine state, body weight, and vaginal membrane condition were evaluated in two studies. In the first study, vaginal membrane and body weight of 15 pregnant subjects were monitored from the ovarian cycle of conception through parturition. There was a significant depression in body weight of 13.3 +/- 3.1 g coincident with vaginal membrane rupture at the estimated time of conception. A second instance of vaginal membrane rupture was found to occur during midpregnancy in 14 of the females. At that time, female body weight showed a significant relative decline of 12.9 +/- 2.4 g. In the second study, treatment of ovariectomized females with estradiol benzoate readily produced rupture of the vaginal membrane and suppressed body weight by 17.9 +/- 1.8 g. It is therefore hypothesized that the observed midpregnancy changes in vaginal membrane condition and body weight identify an interval of increased estrogen stimulation sufficient to produce physiological and behavioral effects in pregnant guinea pigs. Such effects are not readily explained by reference to levels of circulating estrogens or progesterone during pregnancy and therefore may reflect changes in plasma or tissue binding of these steroids.