Abstract
Although a large amount of data concerning microcirculation and cardiovascular disease exists, little is known about microcirculation and hypertension. This is largely due to the difficulty in selectively examining capillaries and metarterioles, independently from small arteries or large vessels.
The physiological role of capillaries and metarterioles, the two elements that make up the microcycle, is peculiar and closely related to metabolic exchange.
During the hypertensive state, several factors can alter these mechanisms. These include elevated plasma viscosity, abnormal membrane properties of red blood cells, and an increase in fibrinogen, LTL and hematocrit levels.
The question of whether an abnormal release of endothelium derived vasoactive factors from capillaries, or an abnormal production of chemical factors by blood cells running through the vasculature area is present in hypertensives is fascinating, but unfortunately neither experimental nor clinical data has yet been able to answer it.
Recently, evidence of the formation of endothelin by red blood cells from endogenous precursors was given, suggesting that red blood cells may modulate the vascular tone both directly, through the release of ATP or endothelin‐1, and indirectly, when hemolysis occurs and hemoglobin is released. The pathological significance of these findings has not been clearly demonstrated in hypertension thus far, although it is reasonable to hypothesise that there are clinical implications for the pathogenesis and the progression of vascular damage during the hypertensive state.
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