ENDOTHELIUM-MEDIATED VASORELAXANT EFFECTS OF CA2-ATPASE INHIBITORS ONTHORACIC AORTA FROM NEONATAL AND ADULT GUINEA-PIGS()

Vasorelaxant effects of Ca2+-ATPase inhibitors were examined in the is olated adult and neonatal guinea pig thoracic aorta focusing on the fu nctional alterations of endothelial cells with development. Cyclopiazo nic acid produced an endothelium-dependent vascular relaxation in the adult aorta preconstricted with norepinephrine, whereas no relaxant re sponse was obtained by the compound in the neonatal preparation. Endot helium-dependent dependent vascular relaxation was also produced by an other Ca2+-ATPase inhibitor, thapsigargin, in the adult aorta, but not in neonatal ones. The endothelium-dependent vascular relaxations prod uced by both Ca2+-ATPase inhibitors ware suppressed either by N-G-nitr o-L-arginine or by methylene blue, suggesting that nitric oxide (NO) m ediated the endothelium-dependent vascular relaxations. The present re sults suggest the possibility that mechanisms underlying the synthesis and/or release of NO change with development in the guinea pig aortic endothelial cells.