Cyclooxygenase-2–Derived Prostaglandin F 2α Mediates Endothelium-Dependent Contractions in the Aortae of Hamsters With Increased Impact During Aging

Abstract

Hypertension and vascular dysfunction result in the increased release of endothelium-derived contracting factors (EDCFs), whose identity is poorly defined. We tested the hypothesis that endothelial cyclooxygenase (COX)-2 can generate EDCFs and identified the possible EDCF candidate. Changes in isometric tension of aortae of young and aged hamsters were recorded on myograph. Real-time changes in intracellular calcium concentrations ([Ca 2+ ] i ) in native aortic endothelial cells were measured by imaging. Endothelium-dependent contractions were triggered by acetylcholine (ACh) after inhibition of nitric oxide production and they were abolished by COX-2 but not COX-1 inhibitors or by thromboxane–prostanoid receptor antagonists. 2-Aminoethoxydiphenyl borate (cation channel blocker) eliminated endothelium-dependent contractions and ACh-stimulated rises in endothelial cell [Ca 2+ ] i . RT-PCR and Western blotting showed COX-2 expression mainly in the endothelium. Enzyme immunoassay and high-performance liquid chromatography-coupled mass spectrometry showed release of prostaglandin (PG)F 2α and prostacyclin (PGI 2 ) increased by ACh; only PGF 2α caused contraction at relevant concentrations. COX-2 expression, ACh-stimulated contractions, and vascular sensitivity to PGF 2α were augmented in aortae from aged hamsters. Human renal arteries also showed thromboxane–prostanoid receptor–mediated ACh- or PGF 2α -induced contractions and COX-2–dependent release of PGF 2α . The present study demonstrates that PGF 2α , derived from COX-2, which is localized primarily in the endothelium, is the most likely EDCF underlying endothelium-dependent, thromboxane–prostanoid receptor–mediated contractions to ACh in hamster aortae. These contractions involved increases in endothelial cell [Ca 2+ ] i . The results support a critical role of COX-2 in endothelium-dependent contractions in this species with an increased importance during aging and, possibly, a similar relevance in humans.