Effects of the antiestrogens, MER-25 and CI 628, on rat and hamster lordosis

Abstract

Antiestrogens were used to test the hypothesis that estrogen exerts a "maintenance," as well as a "priming," effect on rat and hamster sexual receptivity as it apparently does for guinea pigs. MER-25 (75 or 150 mg/kg) significantly reduced rat LQ when given-2 hr OI 8 hr after EB injection. MER-25 given at 34 hr (2 hr prior to I') failed to diminish rat LQ. With hamsters, MER-25 in large doses (7.50 mg/kg) given either at-2 hr or 34 hr reduced lordosis duration to 40% of controls, but this effect was confounded by severe illness among the MER-25 injected animals. Lower doses failed to block behavior, but still produced some toxicity. CI 628 (50 mg/kg) greatly reduced hamster lordosis duration and increased lordosis latency when given 0 hr, but not 34 hr, after EB. The results are consistent with similar previous work on rats and do not support the concept of estrogen "maintenance" in either rats or hamsters. Among ovariectomized rats, hamsters, and guinea pigs, lordosis can be induced by the sequential administration of estrogen and progesterone (Boling and Blandau, 1939; Frank and Fraps, 1945; Dempsey, Hertz, and Young, 1936). Several lines of evidence suggest that estrogen must be available for a number of hours before progesterone is administered in order that the animal be "primed" for a synergistic action of the facilitatory hormones. If the interval between the two hormones is too short, sexual behavior is absent or inadequate (

INDUCTION OF SEXUAL RECEPTIVITY IN OVARIECTOMIZED RATS BY PULSE ADMINISTRATION OF OESTRADIOL-17β

“…However, the oestradiol exposure could be further reduced with no reduction in behavioural effect by giving two pulses of stimulation during the first and the last 4 h of the period of 20 h, although the behavioural effect of the pulses was significantly reduced if the interval between the pulses was prolonged. Neither the suggestion that oestradiol has to be present briefly (the 'trigger hypothesis' of the mechanism of oestradiol action) nor that it has to be present for a prolonged time (the 'maintenance hypothesis') before an ovariectomized rat can respond to progesterone treatment (Arai & Gorski, 1968;Green, Luttge & Whalen, 1970;Whalen & Gorzalka, 1973;McEwen, Pfaff, Chaptal & Luine, 1975;Morin, Powers & White, 1976;Moreines & Powers, 1977;Ydstebtf & Södersten, 1977;Hansen et al, 1978;Johnston & Davidson, 1979;Blaustein, Dudley, Gray, Roy & Wade, 1979), may, therefore, be completely correct. We also found, as did Legan et al (1975), that serum levels of oestradiol declined rapidly when the implants were removed.…”