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Expression of Prostacyclin Receptors in Luteinizing Hormone-Releasing Hormone Immortalized Neurons: Role in the Control of Hormone Secretion¹

Department of Endocrinology, Institute of Pharmacological Sciences (G.E.R., V.C.), University of Milan, Milan, Italy

Address all correspondence and requests for reprints to: Roberto Maggi, Ph.D., Department of Endocrinology, University of Milan, Via G. Balzaretti 9, 20133 Milan, Italy. E-mail: roberto.maggi{at}unimi.it

PGs of the E series are involved in the control of LHRH secretion. The present experiments were conducted to clarify whether PGI₂ (prostacyclin) might be also involved in such a control, using multiple methodological approaches on immortalized LHRH-secreting neurons. A RT-PCR procedure to detect mouse PGI₂ receptor (IP) messenger RNA was first applied, and the results obtained showed the presence of a specific transcript in two cell lines of immortalized LHRH neurons (GT1–1 and GN11 cell lines). Receptor binding assays on membrane preparations from GT1–1 cells showed the presence of a single specific and saturable class of binding sites (K_d = 4.6 nM; 10,000 sites/cell) for [³H]iloprost, a stable analog of PGI₂. Competition experiments showed that the binding sites labeled by [³H]iloprost possess the pharmacological characteristics of IP receptors. In functional studies, PGI₂ and its analogs, iloprost and cicaprost, were able to stimulate LHRH release from the GT1–1 cells with elevated potencies (EC₅₀ = 0.6–4.3 nM); PGE₁ was only slightly less active (EC₅₀ = 28.5 nM), whereas PGE₂, considered the major PG involved in LHRH secretion, was poorly effective (EC₅₀ = 921 nM). The relative potencies (EC₅₀) of these compounds in stimulating the intracellular accumulation of cAMP were in line with their LHRH-releasing activities.

In conclusion, these results indicate that immortalized LHRH-secreting neurons express IP receptors through which PGI₂ may exert relevant effects on LHRH release.

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