Evidence That a Placental Factor Other Than Androsterone or Dihydrotestosterone Inhibits Oestrogen-Induced Lordosis Behaviour in Pregnant Rats

Abstract

Daily administration of oestradiol benzoate, beginning 10 days after mating, stimulates lordosis behaviour in deciduomata-bearing pseudopregnant rats, but not in pregnant rats. The inhibition of this behaviour during pregnancy was not prevented by reducing the number of conceptuses to two, by removing the fetuses while leaving the placentas in utero, or by removing the ovaries and administering progesterone to prevent abortion. Removal of the uterus or fetuses and placentas on day 12, however, led to high levels of lordosis behaviour. Thus, it is likely that the placenta produces a factor which inhibits the behavioural responsiveness to oestrogen. Plasma levels of progesterone, androsterone and dihydrotestosterone were higher during the second half of pregnancy than in the second half of pseudopregnancy prolonged by uterine decidualization. The possible involvement of these steroids in the inhibition of lordosis behaviour was investigated by increasing their levels in deciduomata-bearing pseudopregnant rats and determining the effect on oestrogen-induced lordosis behavior. Little suppression of this behaviour was seen when the pseudopregnant rats were treated with progesterone or androsterone whereas treatment with dihydrotestosterone resulted in a significant inhibition of lordosis behavior. However, the dose of dihydrotestosterone required to do so resulted in high, non-physiological plasma levels of this steroid. No inhibition of lordosis behaviour was observed when dihydrotestosterone levels were approximately threefold those normally present in pregnant rats. It is concluded that none of these three steroids is primarily responsible for the suppression of lordosis behaviour during pregnancy.

Concentrations of testosterone and androsterone in peripheral and umbilical venous plasma of fetal rats

“…Our data confirm the suggestion that the placenta might be a major site for the production of these androgens de Greef et al, 1981 ;Sridaran et ai, 1981). The unexpectedly high levels of androsterone found in fetal (present study) and maternal plasma (de Greef et al, 1981), and the extensive placental steroid metabolism, raises the question whether and in which amounts other 5a-reduced steroid compounds are present in fetal and maternal blood. This could be important since almost all testosterone-binding antisera have some cross reactivity with other steroids.…”

“…Appreciable amounts of androgens occur in the peripheral plasma of pregnant rats de Greef et al, 1981). Our data confirm the suggestion that the placenta might be a major site for the production of these androgens de Greef et al, 1981 ;Sridaran et ai, 1981).…”

“…Appreciable amounts of androgens occur in the peripheral plasma of pregnant rats de Greef et al, 1981). Our data confirm the suggestion that the placenta might be a major site for the production of these androgens de Greef et al, 1981 ;Sridaran et ai, 1981). The unexpectedly high levels of androsterone found in fetal (present study) and maternal plasma (de Greef et al, 1981), and the extensive placental steroid metabolism, raises the question whether and in which amounts other 5a-reduced steroid compounds are present in fetal and maternal blood.…”

“…Plasma androsterone concentrations were measured by RIA (Zamecnik, Barbe, Moger & Armstrong, 1977;de Greef et al, 1981) using the OA-1 antiserum supplied by Dr D. T. Armstrong (London, Ontario, Canada). This antiserum is highly specific for androsterone ; from a variety of 21 steroids only 5oc-androstane-3a,17ß-diol had appreciable cross-reactivity (27%).…”

Regulation of luteal activity in adult female rats treated neonatally with testosterone propionate

“…At the same time two sealed tubes of polydimethylsiloxane filled with progesterone (de Greef & Zeilmaker, 1978; de Greef, Schenck, Vreeburg, van der Vaart & Baum, 1981) were implanted s.c. in five of the TP-treated females. Four days after traumatization of the uterus the rats were killed and the weight of each uterus was determined.…”