Effects of chlorothiazide on forearm vascular responses to norepinephrine

Abstract

The effects of graded doses of norepinephrine on pulse rate, mean blood pressure, forearm blood flow and vascular resistance were studied in normal human subjects before, during, and after chronic administration of chlorothiazide. This drug prevented the negative chronotropic response normally induced by norepinephrine without altering the pressor response. Before giving and after discontinuing chlorothiazide, increasing doses of norepinephrine were associated with progressive decreases in blood flow. After 1 week of chlorothiazide administration, increasing doses of norepinephrine were associated with increases in flow. The results indicate that chlorothiazide decreases the responsiveness of the forearm vessels of normal subjects to the vasoconstrictor effect of norepinephrine. They suggest that chlorothiazide also may modify the effect of norepinephrine on cardiac output. Submitted on December 9, 1960