The Significance of Prostacyclin in Hypertension
The cause of spontaneous hypertension in the rat is still not conclusively explained. In addition to the increased activities of vasopressor hormones, a reduced activity of vasodepressor factors has also been proposed as causal. Among the prostaglandins with a vasodepressor effect, prostacyclin, as the main vascular prostaglandin, probably plays the leading part in blood pressure regulation. Whether it exerts its action locally on the vessel or also systemically in the circulation is still unclear. Locally, prostacyclin synthesis appears to be increased in spontaneously hypertensive rats. In vitro studies (Fig. 28) regularly showed increased aortic prostacyclin formation in the spontaneously hypertensive animals compared with normotensive Wistar rats [20, 197, 204]. The formation of thromboxane A2 was also increased in these animals (Table 3) , so that the suspicion arises that the stimulation of prostacyclin may possibly be of a reactive nature to the change in thromboxane metabolism. In spontaneously hypertensive rats of the “stroke-prone” strain, aortic prostacyclin synthesis was equally increased in both subgroups, the “stroke-prone” and the “stroke-resistant” rats. A fall in aortic prostacyclin synthesis was observed in some rats of the “stroke-prone” strain only with the development of the actual stroke . This finding is possibly explained by the marked atherosclerotic vascular changes in these animals, for with increasing atherosclerosis of the vessels their rate of prostacyclin synthesis continuously declines [47, 95, 139].
KeywordsRenovascular Hypertension Primary Hypertension Spontaneous Hypertension Prostacyclin Synthesis Thromboxane Synthetase
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