Regulation of ANP secretion from isolated atria by prostaglandins and cyclooxygenase-2

Cyclooxygenase (COX) is a key enzyme regulating the production of various prostaglandins (PGs) from arachidonic acid. Angiotensin 11 has been reported to be an important inflammatory mediator, which increases COX-2. The aim of this study was to determine the role of various PGs and COX-2 in the regulation of atrial natriuretic peptide (ANP) secretion. PGF2 alpha and PGD2 caused dose-dependent increases in ANP release and intra-atrial pressure. The potency for the stimulation of ANP secretion by PGF2 alpha was higher than that by PGD2. In contrast, PGE2, PGI2, PGJ2, and thromboxane A2 did not show any significant effects. The increases in intra-atrial pressure and ANP secretion induced by PGF2 alpha and PGD2 were significantly attenuated by the pretreatment with an inhibitor of PGF2 alpha receptor. By the pretreatment with an inhibitor for phospholipase C (PLC), inositol 3-phosphate (IP3) receptor, protein kinase C (PKC), or myosin light chain kinase (MLCK), PGF2 alpha-mediated increase in ANP secretion and positive inotropy were attenuated. Inhibitor for COX-1 or COX-2 did not cause any significant effects on atrial parameters. In hypertrophied rat atria, PGF2 alpha-induced positive inotropy and ANP secretion were markedly attenuated whereas COX-2 inhibitor stimulated ANP secretion. The expression of COX-2 increased and the expression of PGF2 alpha receptor mRNA decreased in hypertrophied rat atria. These results suggest that PGF2 alpha increased the ANP secretion and positive inotropy through PLC-IP3-PKC-MLCK pathway, and the modulation of ANP secretion by COX-2 inhibitor and PGF2 alpha may partly relate to the development of renal hypertension. (C) 2009 Elsevier Inc. All rights reserved.