Abstract
The ability of the Luteinizing Hormone-Releasing Hormone (LH-RH) analogs to displace LH-RH from its pituitary receptors was evaluated in vitro . The two superactive analogs tested showed higher potency than the antagonists and LH-RH itself, D-Trp 6-LH-RH being the most potent. The LH-RH specific binding activity in the pituitary fluctuated throughout the age of the rats. The highest number of LH-RH binding sites were seen on day 35 of age (276 fmol × 10 −2/pit) and an increment was induced by 0.05 μg D-Trp 6-LH-RH (400 fmol × 10 −2/pit). However, 1 μg D-Trp 6-LH-RH reduced the binding of LH-RH at all the times studied. In the control animals the number of estradiol binding sites increased on day 42 of age, and 0.05 μg D-Trp 6-LH-RH augmented them on day 35 of age. On the contrary, 1 μg D-Trp 6-LH-RH diminished the estradiol uterine receptors at all the times studied. Similar results were obtained in the ovariectomized-hypophysectomized rats on day 35 of age. Our studies demonstrated a biphasic action of D-Trp 6-LH-RH on LH-RH pituitary receptors and a direct effect on uterus which could be mediated through the uterine estradiol receptors.
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