Here's a study

Disparate effect of clomiphene and tamoxifen on pituitary gonadotropin release in vitro.

Adashi EY, Hsueh AJ, Bambino TH, Yen SS.

The direct effects of clomiphene citrate (Clomid), tamoxifen, and estradiol (E2) on the gonadotropin-releasing hormone (GnRH)-stimulated release of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were studied in cultured anterior pituitary cells obtained from adult ovariectomized rats. Treatment of pituitary cells with Clomid or enclomid (10(-8) M) in vitro for 2 days resulted in a marked sensitization of the gonadotroph to GnRH as reflected by a 6.5-fold decrease in the ED50 of GnRH in terms of LH release from 2.2 x 10(-9) M in untreated cells to 3.6 x 10(-10) M. Treatment with E2 or Clomid also increased the sensitivity of the gonadotroph to GnRH in terms of FSH release by 4.3- and 3.3-fold respectively. Tamoxifen, a related antiestrogen, comparable to Clomid in terms of its ability to compete with E2 for pituitary estrogen receptors, was without effect on the GnRH-stimulated LH release at a concentration of 10(-7) M. Furthermore, tamoxifen, unlike Clomid, caused an apparent but not statistically significant inhibition of the sensitizing effect of E2 on the GnRH-stimulated release of LH. Our findings suggest that Clomid and its Enclomid isomer, unlike tamoxifen, exert a direct estrogenic rather than an antiestrogenic effect on cultured pituitary cells by enhancing the GnRH-stimulated release of gonadotropin.

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