Augmentation of Pituitary Responsiveness to LH-Releasing Hormone (LH-RH) by Estrogen

Abstract

The effect of pretreatment with estrogen on the LH-RH-induced release of LH was investigated in diestrous rats. Ten or 20 μg of estradiol benzoate in oil were injected into 5-day cycling female rats on day 1 (diestrus). On day 2 (diestrus) 0.1 μg of highly purified porcine LH-releasing hormone (LH-RH) was injected into the carotid artery. Serum LH levels before and 20 min after the injection were determined by radioimmunoassay. In oil-pretreated rats, LH-RH injection induced only a slight rise of serum LH as compared to the preinjection levels. In the estrogen-pretreated rats, the same dose of LH-RH induced a much greater rise in serum LH levels. Estrogen by itself did not affect the level of serum LH. The results suggest that pretreatment with estrogen results in an increased responsiveness of the pituitary to LH-RH in diestrous rats.