title: Co-expression of adrenomedullin and adrenomedullin receptors in rat epididymis: distinct physiological actions on anion transport.
abstract: Adrenomedullin (AM) has been found in the brain as well as in various peripheral tissues, including reproductive organs such as the testis and the prostate. Here, we report the expression of AM in the rat epididymis and its role in anion secretion. Whole-epididymal extracts had 35.3 +/- 1.4 fmol of immunoreactive AM per mg of protein, and immunocytochemical studies showed positive AM immunostaining in the epithelial cells. By solution-hybridization-RNase protection assay, preproAM mRNA was detected at high levels in the epididymis. Gel filtration chromatography of AM showed two peaks, with the predominant one eluting at the position of authentic rat AM (1-50). Specific binding of AM to the epididymis, which could be displaced by calcitonin gene-related peptide, was observed. The epididymis also bound to calcitonin gene-related peptide, and this was displaceable by AM. Furthermore, the epididymis was shown to co-express mRNA encoding the calcitonin receptor-like receptor and receptor activity-modifying proteins, RAMP1/RAMP2. The corpus region had the highest AM level and gene expression and the lowest active peptide:precursor ratio. However, mRNA levels of the receptor and the receptor activity-modifying proteins were similar in all regions. In monolayer cultures derived from the rat epididymal cells, AM stimulated short-circuit current on the luminal side in a dose-dependent manner. Our results demonstrate the presence of AM, preproAM mRNA, AM receptors, and specific-binding sites in the rat epididymis as well as the possible role of AM in the regulation of electrolyte and fluid secretion in the epididymis.
authors.affiliation: Department of Physiology, Faculty of Medicine, The University of Hong Kong, Hong Kong, China.
authors.forename: Isabel S S
authors.initials: IS
authors.lastname: Hwang
authors.forename: Dominic J
authors.initials: DJ
authors.lastname: Autelitano
authors.forename: Patrick Y D
authors.initials: PY
authors.lastname: Wong
authors.forename: George P H
authors.initials: GP
authors.lastname: Leung
authors.forename: Fai
authors.initials: F
authors.lastname: Tang
mesh_terms: D053607:Adrenomedullin; D000818:Animals; D027321:Anion Transport Proteins / Q000502:physiology*; D001665:Binding Sites; D015740:Calcitonin Gene-Related Peptide / Q000494:pharmacology; D002478:Cells, Cultured; D002850:Chromatography, Gel; D004822:Epididymis / Q000187:drug effects / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis; D023282:Nuclease Protection Assays; D010455:Peptides / Q000378:metabolism*; D011498:Protein Precursors / Q000096:biosynthesis; D011863:Radioimmunoassay; D051381:Rats; D017207:Rats, Sprague-Dawley; D058262:Receptor Activity-Modifying Protein 1; D058263:Receptor Activity-Modifying Protein 2; D058261:Receptor Activity-Modifying Proteins; D058265:Receptors, Adrenomedullin; D018015:Receptors, Calcitonin Gene-Related Peptide / Q000378:metabolism; D018000:Receptors, Peptide / Q000096:biosynthesis*
chemical_list: D027321:Anion Transport Proteins; D047908:Intracellular Signaling Peptides and Proteins; D007457:Iodine Radioisotopes; D008565:Membrane Proteins; D010455:Peptides; D011498:Protein Precursors; C545508:Ramp1 protein, rat; C545509:Ramp2 protein, rat; D058262:Receptor Activity-Modifying Protein 1; D058263:Receptor Activity-Modifying Protein 2; D058261:Receptor Activity-Modifying Proteins; D058265:Receptors, Adrenomedullin; D018015:Receptors, Calcitonin Gene-Related Peptide; D018000:Receptors, Peptide; D053607:Adrenomedullin; D015740:Calcitonin Gene-Related Peptide