AGONIST AND ANTAGONIST ACTIVITY OF EN-CLOMIPHENE UPON OESTROGEN-MEDIATED EVENTS IN THE UTERUS, PITUITARY GLAND AND BRAIN OF THE RAT

Abstract

The oestrogen agonist and antagonist activity of a single dose of en-clomiphene (0·5–50 mg/kg) was studied in peripheral and brain tissue in the 3 week ovariectomized rat. 17β-Oestradiol benzoate (100 pg/kg) or vehicle was injected 24 h after en-clomiphene administration and data collected at 72 h. En-clomiphene produced a dose-related (agonist) fall in body weight and food intake. Agonist action was not observed upon sexual receptivity and prolactin secretion; oestrogen antagonism of these parameters was only seen at the higher doses. The effects of en-clomiphene upon serum LH and FSH were complex, both agonist and antagonist activity being demonstrated in the absence and presence of oestrogen. En-clomiphene was uterotrophic at all doses tested; however, oestrogen antagonism was only seen at the higher doses. Inhibition of the accumulation of uterine luminal fluid at the higher doses of en-clomiphene was a sensitive index of oestrogen antagonism. The results are discussed in relation to previous studies of the effects of enclomiphene on oestrogen receptors. With the exception of the antagonism of oestrogen-induced sexual receptivity no correlation could be made between biological activity and the status of oestrogen receptors in tissue.