Changes in Pituitary Responsiveness to Luteinizing Hormone-Releasing Hormone (LH-RH) in Anestrous Ewes Pretreated with Estradiol Benzoate1

Abstract

Mature, whitefaced ewes maintained in an anestrous reproductive state were divided into four groups which received oil, 25 µg estradiol benzoate (EB), 250 µg EB, and 500 µg EB, respectively. Twenty hours after pretreatment with EB, 3.0 µg LH-RH was administered intracarotidly. The highest LH value after LH-RH administration minus the preinjection LH value yielded Δ LH in nanograms per milliliter which was used as the experimental index of pituitary responsiveness to LH-RH. Pretreatment with 250 µg EB increased baseline levels of LH. Doses of 250 and 500 µg EB augmented increased LH release due to LH-RH administration as compared to the oil and 25 µg EB pretreated ewes. The present results support the hypothesis that part of the LH-release augmenting effect of estrogens may be due to an increase in pituitary responsiveness to LH-RH.