| Research Abstract |
The kidney plays a key role in the development and the maintenance of hypertension. We studied the pathophysiological role of renal vasoactive substances. Renin-angiotensin, kallikrein-kinin, prostaglandins and cytochrome P450 systems are localized to specific nephron segments, suggesting the intimate relationship between these substances and the nephron segments in which that localized. There were marked age-dependent changes in the production rate of these substances. The changes are also dependent on the maturation and the differentiation of the nephron. Furthermore, there were significant changes of production rates of these substances in the animal model of hypertension, such as spontaneously hypertensive rats and Dahl salt sensitive rats. The production rate of vasodepressor substances, such as kallikrein-kinin and prostaglandins systems decreased in hypertensive subjects. On the contrary, the production rate of 19-hydroxyeicosatetraenoic acid (HETE) and 20-HETE which synthesized
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by renal cytochrome P450, the third metabolic pathway of arachidonic acid increased in hypertensive subjects. 20-HETE constricts the microdissected afferent arteriole, and EET mediate the vasodilation through the angiotensin II type II receptor in the afferent arteriole, suggesting these substances regulate the vascular resistance. In addition, prostacyclin synthesized by cyclooxygenase inhibits and epoxyeicosatrienoic acids (EETs) synthesized by cytochrome P450 stimulate the cell growth of vascular smooth muscle cells and glomerular mesangial cells in culture. When arachidonic acid is synthesized by cyclooxygenase, the cell growth is inhibited and when arachidonic acid is synthesize by cytochrome P450, the cell growth is stimulated.In hypertensive subjects prostacyclin, the cyclooxygenase products is decreased and cytochrome P450 activity is increased. These results suggest that these vasoactive substances have the role of the regulation of the vascular resistance, the development of renal damage and the vascular damage in hypertensive subjects. Less
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