Influences of endothelium on the time course of noradrenaline-, 5-HT-, prostaglandin F2alpha- and high-K+-induced contractions in aortae of WKY and SHRSP.

Influences of endothelium on contraction of aortic smooth muscle by various agents were studied and those in the preparations from Wistar Kyoto rat (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) were compared. Endothelium depressed the contractions induced by noradrenaline and 5-hydroxytryptamine (5-HT). The time course of the contraction was bi- or tri-phasic in the former and slow rising monophasic in the latter. On the other hand, the depression was weaker in the contraction by prostaglandin F2alpha- and high K+. The depression was blocked by the removal of endothelium or in the presence of Nomega-nitro-L-arginine (L-NNA), indicating that nitric oxide (NO) released from endothelium was responsible for the inhibition. The inhibition was weaker in the preparation from SHRSP when compared to that in the preparation from WKY. Relaxation by acetylcholine (ACh) of the preparation precontracted in the presence of respective contractile agent was impaired in the preparation from SHRSP. It is concluded that mode of inhibition of the contraction varies depending on the agents used to initiate the contraction, i.e. depending on the mode of the release of NO. In the preparation from SHRSP, the influence of endothelium is impaired due to the reduced release of NO.