Real-time quantitative PCR study of genes involved in the generation of endothelium-depedent contractions in the aorta of the spontaneously hypertensive rat

Activation of muscarinic receptors by acetylcholine causes larger endothelium-dependent contractions in arteries of spontaneously hypertensive (SHR) than normotensive (WKY) rats. Such endothelium-dependent contractions involve the release of endoperoxides and prostacyclin which activate thromboxane-prostanoid (TP) receptors on the vascular smooth muscle (VSM). The present study aimed to define whether or not the expression of the different muscarinic receptor subtypes (m1-m5) differs in aortic endothelial cells (EC) of the SHR. The mRNA expression of cyclooxygenase-1 (COX-1), prostacyclin synthase and thromboxane synthase, and of prostacyclin and TP-receptors was measured, using real-time PCR, in freshly isolated EC and VSM. The expression of the five muscarinic receptor subtypes in EC was comparable in the two strains. The abundance of the individual muscarinic subtypes in descending order was: m3>m2>m1, with little to no m4 or m5 expressed. The mRNA expression of COX-1 and of prostacyclin and thromboxane synthases was elevated in EC of SHR. The gene expression of prostacyclin or TP-receptors was comparable in VSM of the two strains. These data suggest that an alteration in muscarinic receptors on EC is unlikely to explain the enhanced endothelium-dependent contractions in the SHR. However, an elevated expression of COX-1 and of prostacyclin and thromboxane synthases probably contribute to the greater production of endothelium-derived prostanoids observed in arteries of the hypertensive rats