Effect of the venodilated state on sympathetic-induced venoconstriction in normal subjects.

The interaction between venoconstriction induced by application of ice to the forehead and nitroglycerin-induced venodilation was examined in 19 healthy male volunteers, ages 25 +/- 5 years (mean +/- standard deviation). Venous tone was determined by the equilibration technique. Mercury-in-silastic plethysmography was used to measure changes in forearm volume before and after ice application during control conditions, and before and after ice application in the venodilated state (nitroglycerin spray, 0.8 mg). Venous tone and arterial pressure increased significantly after the application of ice to the forehead in both the control and venodilated states, indicating that ice increased sympathetic tone. Nitroglycerin increased venous volume by 0.28 cc/100 cc arm. The venoconstrictive effect of ice after nitroglycerin (a decrease in venous volume of 0.53 cc/100 cc arm) was quantitatively similar to the venoconstrictive effect of ice during control conditions (a decrease in venous volume of 0.54 cc/100 cc arm). These results suggest that sympathetic-induced venoconstriction is not attenuated in the venodilated state.