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This Article Full Text Full Text (PDF) All Versions of this Article: 68/6/2005    most recent biolreprod.102.011015v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hwang, I. S.S. Articles by Tang, F. Search for Related Content PubMed PubMed Citation Articles by Hwang, I. S.S. Articles by Tang, F. Agricola Articles by Hwang, I. S.S. Articles by Tang, F.

Co-Expression of Adrenomedullin and Adrenomedullin Receptors in Rat Epididymis: Distinct Physiological Actions on Anion Transport¹

Department of Physiology,⁵ Faculty of Medicine, The University of Hong Kong, Hong Kong, China Molecular Physiology Laboratory,⁶ Baker Medical Research Institute, Melbourne, Victoria 8008, Australia Department of Physiology,⁷ Faculty of Medicine, The Chinese University of Hong Kong, Hong Kong, China

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.

¹ Supported by a University Block Grant 344/034/0005 and a CRCG grant from the University of Hong Kong.

² Correspondence: Fai Tang, Department of Physiology, Faculty of Medicine, The University of Hong Kong, 21 Sassoon Road, Poktulam, Hong Kong, China. FAX: 852 2855 9730; ftang{at}hkucc.hku.hk

³ Current address: C.K. Life Sciences Ltd., 2 Dai Fu Street, Tai Po Industrial Estate, Tai Po, New Territories, Hong Kong, China

⁴ Current address: Cryptome Research Pty. Ltd., P.O. Box 6492, St. Kilda Road Central, Melbourne, Victoria 8008, Australia