Endogenous opioids participate in the regulation of gonadotropin secretion through an influence on the release of the hypothalamic LHRH. However, it is not clear whether opioids exert a direct effect on LHRH-producing neurons or interfere with other systems able to influence LHRH release. A neuronal LHRH-producing cell line (GT1) developed recently provides a good model to study the mechanisms controlling LHRH release. In the present study, the presence of opioid receptors on a subclone of GT1 cells (GT1-1) has been investigated. A specific and saturable binding of the 3H-labeled nonselective opioid ligand diprenorphine ([3H]DIP) was detected by a receptor binding assay on both intact GT1-1 cells and crude membrane preparations obtained from these cells. Analysis of saturation curves revealed that [3H]DIP apparently binds to a single class of sites with a Kd of 0.2 nM and a binding capacity of 125 fmol/mg protein, corresponding to approximately 20,000 sites/cell. Selective displacement of the binding of [3H]DIP to GT1-1 cells by [D-Ala2,N-Me-Phe4,Gly5-ol]enkephalin, [D-Pen2,D-Pen5]enkephalin (DPDPE), and U50488H, which are selective ligands, respectively, for mu-, delta-, and kappa-receptors, was also evaluated. Only the specific delta-ligand DPDPE produced a significant inhibition of the binding of [3H]DIP. [D-Ala2,N-Me-Phe4,Gly5-ol]Enkephalin and U50488H were totally ineffective. The inhibitory effect of the agonist DPDPE on the binding of [3H]DIP was decreased by the presence of sodium ions, a typical characteristic of the binding of agonists to opioid receptors. Finally, it has been observed that treatment with prostaglandins E1 and E2 produces a dramatic increase in cAMP accumulation in GT1-1 cells, and DPDPE is highly effective in suppressing this effect. On the basis of these results, it is possible to postulate the presence of functional delta-opioid receptors on GT1-1 cells. By extrapolation, one might suggest that endogenous opioids may affect LHRH neurons by two mechanisms: a direct one, acting via delta-receptors, and an indirect one, through the activation of neurons impinging on the LHRH system, which uses mu-receptors.
Characterization of functional opioid delta receptors in a luteinizing hormone-releasing hormone-producing neuronal cell line / R. Maggi, F. Pimpinelli, L. Martini, F. Piva. - In: ENDOCRINOLOGY. - ISSN 0013-7227. - 136:1(1995 Jan), pp. 289-295.
|Titolo:||Characterization of functional opioid delta receptors in a luteinizing hormone-releasing hormone-producing neuronal cell line|
MAGGI, ROBERTO (Primo)
PIMPINELLI, FEDERICA ALBERTA ELENA MARIA (Secondo)
MARTINI, LUCIANO (Penultimo)
PIVA, FLAVIO (Ultimo)
|Parole Chiave:||Animals ; Neurons ; Cyclic AMP ; Receptors, Opioid, delta ; Gonadotropin-Releasing Hormone ; Cell Membrane ; Mice ; Enkephalin, D-Penicillamine (2,5)- ; Enkephalins ; Cell Line|
|Settore Scientifico Disciplinare:||Settore BIO/09 - Fisiologia|
|Data di pubblicazione:||gen-1995|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1210/en.136.1.289|
|Appare nelle tipologie:||01 - Articolo su periodico|