A re-examination of the lordosis response in female rats given high doses of testosterone propionate or estradiol benzoate in the neonatal period

Abstract

High lordosis quotients (LQ) were observed when female Wistar rats injected with 1.25 mgm of testosterone propionate (TP) on Day 4 of postnatal life were tested as intact adults. The high LQ was not due to testing during the lights-on period, the age at which the females were tested, the use of a strain that was insensitive to the masculinizing action of TP or estradiol benzoate (EB), the age at which the females were injected with TP or EB, or an abnormal response to estrogen. High LQ values were found in similar tests on adult female rats of two other strains injected with 1.25 mgm TP on Day 4 of life. A marked reduction of the facilitatory action of progesterone on receptivity in estrogen-primed animals was demonstrated in the females of all three strains treated with TP or EB during the neonatal period and for males after castration as adults. Analysis of the experimental records of the mating tests showed that females anovulatory following TP or EB administration during the neonatal period and tested either intact and under the influence of endogenous hormones or under the influence of exogenous estrogen showed a rapid and highly significant increase in receptivity during the course of prolonged (20 min) tests with two or three active stimulus males. This effect was very much reduced if the treated females were under the influence of exogenous estrogen plus progesterone. The effect was not seen in males castrated as adults and treated with estrogen, or in females not treated with steroids in the neonatal period and tested intact at proestrus alone or under the influence of exogenous steroids after ovariectomy. A significant increase in LQ during the test period was observed in females of the Wistar strain which were anovulatory as a result of exposure to constant light and were tested intact without any exogenous hormone being administered. It is suggested that although tests involving a limited number of mounts or attempts to mount at low rates over a short period of time may be adequate to determine the degree of receptivity of normal female rats they are not adequate to establish the capacity of female rats treated with steroid hormones during the neonatal period to display the lordosis response.