Alterations induced by clomiphene in the concentrations of oestrogen receptors in the uterus, pituitary gland and hypothalamus of female rats.

Alterations in the concentrations of oestrogen receptors in the uterus, pituitary gland and hypothalamus during the 2 weeks following a single administration of clomiphene citrate (Clomid) to immature, bilaterally ovariectomized rats were investigated. Examination of the uterine wet weight at 1, 7 and 14 days following a single injection of Clomid (100 micrograms, 250 micrograms or 10 mg) indicated significant time- and dose-related increments from a control value of 45 +/- 2 (S.E.M.) mg to a maximum of 123 +/- 3 mg (250 micrograms dose at 14 days). In contrast, a single injection of oestradiol led to a transient increase in the uterine weight on day 1 to 94 +/- 6 mg, but was without effect by days 7 and 14. Analysis of the uterine DNA content 7 and 14 days after treatment with Clomid revealed significant increments from control values of 390 +/- 10 micrograms to a high level of 558 +/- 9 micrograms (10 mg dose at 7 days). There was a transient retention of nuclear oestrogen receptors and rapid replenishment of cytoplasmic oestrogen receptors in less than 24 h in the uteri of animals treated with oestradiol (25 micrograms), but determinations of receptor content in Clomid-treated animals revealed prolonged retention of nuclear receptors and delayed replenishment of cytoplasmic receptors. The duration and extent of retention of nuclear receptors and depletion of cytoplasmic receptors after treatment with Clomid were found to be dose-dependent. Fourteen days after Clomid treatment, levels of oestrogen receptors in nuclei from the uterus were still raised in all treatment groups, whereas replenishment of cytoplasmic receptors was complete in animals treated with the lower doses (100 and 250 micrograms) of Clomid. A single injection of Clomid (250 micrograms) induced similar prolonged retention of nuclear receptors and delayed depletion of cytoplasmic receptors in pituitary tissue. In contrast, changes in the content of oestrogen receptors in the hypothalamus following Clomid treatment were minimal. The limited effect of Clomid on hypothalamic tissue may mean that the pituitary gland is a more important target for this compound than is the hypothalamus. The findings have confirmed earlier reports on the long-term uterotrophic effect of Clomid and have suggested that under these long-term, in-vivo conditions, Clomid acts in the uterus and pituitary gland as a long-acting oestrogen characterized by prolonged retention of oestrogen receptors in the nucleus and delayed, but otherwise effective, replenishment of the oestrogen receptors in the cytoplasm.