THE RELAXANT EFFECT OF ADRENOMEDULLIN ON PARTICULAR SMOOTH MUSCLES DESPITE A GENERAL EXPRESSION OF ITS MESSENGER-RNA IN SMOOTH-MUSCLE, ENDOTHELIAL AND EPITHELIAL-CELLS

1 By use of the reverse transcription polymerase chain reaction (RT-PC R), we determined the expression of adrenomedullin (AM) mRNA in the va rious tissues of the pig. To evaluate the significance of the expressi on of AM mRNA, we also determined the effects of AM on the cytosolic C a2+ concentration ([Ca2+](i)) and tension development of the porcine s mooth muscle strips obtained from the coronary artery, pulmonary vein, trachea, ileum and urinary bladder. 2 AM mRNA was widely expressed in the porcine tissues examined, which included myocardium (left and rig ht ventricle and right atrium), kidney, lung endothelial cells (aorta and aortic valve), smooth muscles (aorta, main pulmonary artery, pulmo nary vein, renal artery and vein, coronary artery, ileum, trachea and urinary bladder) and epithelial cells (trachea and urinary bladder). 3 AM induced a decrease in [Ca2+](i) and tension of the coronary artery , but not the pulmonary vein. AM had no effects on either the [Ca2+](i ) or tension of the trachea and urinary bladder strips or on the tensi on development of strips of ileum. 4 These results indicated that AM h as a role as an autocrine and/or paracrine regulator of the coronary a rterial tone. AM probably does not have an important role in the regul ation of the pulmonary venous, tracheal, ileac and urinary bladder smo oth muscle tone, even though AM, mRNA is expressed in these tissues; t he functional significance of AM in these smooth muscles remains to be determined.