Adrenomedullin Receptor Is Found Exclusively in Noradrenaline‐Secreting Cells of the Rat Adrenal Medulla

Abstract

Adrenomedullin, originally identified in the adrenal medulla, has binding sites in the adrenal gland; however, its role in the adrenal medulla is unclear. This study was designed to characterise adrenomedullin binding sites in the rat adrenal medulla, using ligand binding studies, immunocytochemistry, and mRNA analysis. A single population of specific adrenomedullin receptors was identified in adrenal medullary homogenates. 125 IAdrenomedullin was displaced only by adrenomedullin and not by calcitonin gene-related peptide or amylin at concentrations up to 100 nmol/L. The receptor K D was 3.64 nmol/L with a receptor density of 570 fmol/mg of protein. Analysis of mRNA revealed that the genes encoding both the putative adrenomedullin receptors, termed calcitonin receptor-like receptor (CRLR) and L1, were expressed in the rat adrenal medulla. Dual-colour indirect-labelled immunofluorescence was used to localise phenylethanolamine N-methyltransferase (PNMT) and the adrenomedullin receptor in the same section. PNMT is the enzyme that converts noradrenaline to adrenaline and is not expressed in noradrenaline-secreting cells. These studies revealed that both CRLR and L1 were expressed only in cells that did not express PNMT, suggesting that adrenomedullin receptors are only found in noradrenaline-secreting cells. Further evidence to support this conclusion was provided by the demonstration of colocalisation of adrenomedullin receptors with dopamine ␤-hydroxylase, confirming the presence of the receptors in medullary chromaffin cells. Taken together, these data suggest that adrenomedullin acts through a specific adrenomedullin receptor in the rat adrenal medulla. RT-PCR and northern blot analysis revealed greater abundance of mRNA for L1 than for CRLR, possibly suggesting that L1 may be the major adrenomedullin receptor expressed in this tissue. As it has been reported that adrenomedullin is synthesised predominantly by adrenaline-secreting cells, it appears likely that adrenomedullin is a paracrine regulator in the adrenal medulla. Key Words: Adrenomedullin receptor-Phenylethanolamine N-methyltransferase -Chromaffin cells.

Catecholamine-synthesizing enzymes in the adult and prenatal human testis

“…Because neurofilament proteins are not synthesized by typical chromaffin cells (Ehrlich et al 1994;Unsicker et al 1989;Renshaw et al 2000;Ersenberger et al 2005), the Leydig cells of the human testes resemble both adrenal chromaffin cells and sympathetic neurons (Bohn et al 1982(Bohn et al , 1984. The Leydig cells express the PNMT gene (Bohn et al 1982; this study), glucocorticoid receptors (Evain et al 1976;Saez et al 1977; our unpublished results), a variety of neuroactive substances, which are typical for chromaffin cells, and also the neurofilament triplet proteins, which are characteristic of sympathetic nerve cells (Davidoff et al , 1999(Davidoff et al , 2004.…”

Regulation of Calcium Channels and Exocytosis in Mouse Adrenal Chromaffin Cells by Prostaglandin EP3 Receptors

“…The remainder lack phenylethanolamine N-methyltransferase and are termed "noradrenergic." There is evidence for differential expression of GPCRs in adrenergic versus noradrenergic cells (Renshaw et al, 2000), so it is interesting to speculate that EP3 receptor expression might be limited to the adrenergic cells and preferentially modulate epinephrine release. Further work is required to determine whether this is the case.…”

Pathophysiological Function of Adrenomedullin and Proadrenomedullin N-Terminal Peptides in Adrenal Chromaffin Cells

“…]AM have been detected by autoradiography in the rat adrenal medulla, and have been shown to be displaced by low concentrations of AM, AM or CGRP with similar potency, suggesting that AM reacts with receptors which recognize both AM and CGRP (41). An abundance of [ 125 I]AM-binding sites have also been detected in the membrane fraction of the rat adrenal medulla (42). These sites were of high affinity with a Kd of 3.64 nmol/l and were displaced only by AM, but not by CGRP, indicating that the receptors were specific to AM.…”