The Vascular Effect of the Thiazide Diuretics

Abstract

While it seems likely that the fall in blood pressure produced by the thiazide diuretics is a consequence of their sustained diuretic action, it has not been possible to demonstrate this with certainty, and the mode of action of diuretics in reducing blood pressure remains unexplained. Although there is a reduction in extracellular fluid and plasma volumes over the first few days after the drug is administered,^1-3 these are later restored to their initial levels.^4-7 Furthermore, it has been shown that cardiac output, though initially reduced, returns to normal levels after a period of weeks of continued therapy. Since the blood pressure continues to be reduced, the calculated total peripheral resistance is also reduced, and it has been inferred that the drug affects the blood vessels themselves.⁶ The purpose of this report is to acquire direct evidence by plethysmography for this action on the peripheral blood vessels