Effect of clomiphene citrate on the in vitro release of LH and FSH by the pituitary gland of the long-term ovariectomized rat pretreated with LRH or with LRH and oestradiol benzoate.

The effect of a combined in vivo pre-treatment with luteinizing hormone-releasing hormone (LRH) and either oestradiol benzoate (OB), clomiphene (-citrate) or OB plus clomiphene on the autonomous and the supramaximally LRH-stimulated in vitro secretion of LH and FSH by pituitary glands of long-term ovariectomized (OVX) rats was studied using a hemipituitary perifusion system. The concentration of LRH in the perifusion medium was 1 microgram/ml. Pre-treatment with LRH during 5 days was effected by means of sc implanted Alzet osmotic minipumps; control rats received a piece of silastic with the dimensions of a minipump. OB, 3 micrograms/injection, clomiphene 100 micrograms/injection or solvent were given on days 2 and 4 (day of perifusion: day 5). In rats not pre-treated with LRH neither OB, nor clomiphene changed the content of the pituitary gonadotropin stores. There was only a small but significant positive effect of the combined treatment with OB and clomiphene on the pituitary FSH content. LRH (partly) depleted the gonadotropin stores. This effect of LRH was potentiated by OB, but not by clomiphene. Clomiphene prevented the depletion-potentiating effect of OB. OB raised the LRH-stimulated secretion of LH and FSH as well as the autonomous secretion of LH. Clomiphene raised the LRH-stimulated (not the autonomous) secretion of LH and FSH. OB plus clomiphene had the same effect as OB alone. Clomiphene also raised the LRH-stimulated secretion of LH and FSH after pre-treatment with LRH, but OB did not do so: LRH prevented the stimulatory effect of OB but not of clomiphene. OB plus clomiphene had the same effect as OB alone.(ABSTRACT TRUNCATED AT 250 WORDS)