Similar luteinizing hormone-releasing hormone binding sites in rat anterior pituitary and ovary.

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Abstract
To study the luteinizing hormone-releasing hormone (LH-RH; luliberin) receptors in the rat anterior pituitary gland and ovary, 125I-labeled [D-Ser(TBU)6des-Gly-NH210]LH-RH ethylamide was used as a labeled ligand. The binding characteristics were assessed by Scatchard analysis of labeled ligand binding and by potency displacement with unlabeled peptides. Similar Kd values, 0.1-0.3 nM, were found for the labeled and unlabeled peptides in both tissues. A similar order of potency was observed between the binding affinity of 15 peptides in anterior pituitary and ovarian homogenates and their biological activity on luteinizing hormone [lutropin, LH] release in rat anterior pituitary cells in culture. The LH-RH receptors present in the rat ovary apparently have a specificity similar to that of the anterior pituitary LH-RH receptor controlling secretion of LH and follicle-stimulating hormone [follitropin]. The binding affinities of the LH-RH agonists and antagonists can account, at least up to a large extent, for their relative biological potencies. Although there definitely are specific LH-RH receptors in the ovary which may play a role in the antifertility effects observed after administration of LH-RH agonists, the possible physiological significance of these ovarian receptors is still unknown and of great biological interest.