Enhanced Adrenomedullin Production by Mechanical Stretching in Cultured Rat Cardiomyocytes

Abstract

Abstract —Adrenomedullin (AM) is secreted from cultured cardiac myocytes. In this study, we examined whether mechanical stretching stimulates AM production in cardiac myocytes, and if so, whether angiotensin II (Ang II) is involved in that mechanism. Neonatal rat cardiac myocytes cultured in serum-free medium were stretched 10% or 20% on flexible silicone rubber culture dishes, and AM mRNA expression was examined by quantitative polymerase chain reaction. The AM mRNA levels in the myocytes stretched 10% and 20% for 24 hours significantly increased by 56% ( P <0.05) and 88% ( P <0.01), respectively, when compared with the levels in nonstretched cells. AM secretion into the medium after the myocytes were stretched 10% and 20% increased by 22% ( P <0.05) and 45% ( P <0.01), respectively. In nonstretched myocytes incubated with 10 −6 mol/L Ang II for 24 hours, AM mRNA and secretion increased by 86% ( P <0.05) and 36% ( P <0.01), respectively. These effects of Ang II were abolished by 10 −6 mol/L CV-11974, an Ang II type I (AT 1 ) receptor antagonist, but not by 10 −6 mol/L PD-123319, an Ang II type II antagonist. Stretch-induced increases of AM gene expression and secretion were significantly inhibited ( P <0.05) in the presence of 10 −6 mol/L CV-11974 by 46% and 52%, respectively; however, they were not affected by 10 −6 mol/L PD-123319. These findings indicate that AM production from cardiac myocytes is augmented by mechanical stretching, partially through the AT 1 receptors, which suggests a local interaction between AM and the renin-angiotensin system in stretched cardiac myocytes.