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 μg, 250 μg 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 μg 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 μg to a high level of 558 ± 8 μg (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 μg), 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 μg) of Clomid.

A single injection of Clomid (250 μg) 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.

Ovulation-selective/specific genes, that is, genes preferentially or exclusively expressed during the ovulatory process, have been the subject of growing interest. We report herein studies on the use of suppression subtractive hybridization (SSH) to construct a ‘forward’ ovulation-selective/specific cDNA library. In toto, 485 clones were sequenced and analyzed for homology to known genes with the basic local alignment tool (BLAST). Of those, 252 were determined to be nonredundant. Of these 252 nonredundant clones, 98 were analyzed by probing mouse preovulatory and postovulatory ovarian cDNA. Twenty-five clones (26%) failed to show any signal, and 43 cDNAs tested thus far display a true ovulation-selective/specific expression pattern. In this communication, we focus on one such ovulation-selective gene, the fatty acid elongase 1 (FAE-1) homolog, found to be localized to the inner periantral granulosa and to the cumulus granulosa cells of antral follicles. The FAE-1 gene is a β-ketoacyl-CoA synthase belonging to the fatty acid elongase (ELO) family, which catalyzes the initial step of very long-chain fatty acid synthesis. All in all, the present study accomplished systematic identification of those hormonally regulated genes that are expressed in the ovary in an ovulation-selective/specific manner. These ovulation-selective/specific genes may have significant implications for the understanding of ovarian function in molecular terms and for the development of innovative strategies for both the promotion of fertility and its control.