Effects of environmental temperature on the venodilatory response to nitroglycerin

The venodilatory response to nitroglycerin (0.8 mg sublingually) was measured in 10 healthy young male volunteers in a cool [24.3 ± 0.6°C skin temperature (T(sk))] and a warm environment (34.7 ± 0.2°C T(sk)). Nitroglycerin caused mean arterial pressure to fall and heart rate to rise in both the cool (105 ± 2 to 96 ± 3 mmHg; 55 ± 3 to 62 ± 3 beats/min) and the warm environment (87 ± 3 to 81 ± 3 mmHg; 66 ± 4 to 75 ± 3 beats/min), but the fall in pressure was greater in the cool than in the warm environment. Forearm blood flow was reduced and forearm vascular resistance elevated in the cool (117 ± 19 units; 1.15 ± 0.08 ml · 100 cc arm^-1 · min^-1) compared with the warm environment (15 ± 3 units; 8.60 ± 1.89 ml · 100 cc arm^-1 · min^-1). Nitroglycerin caused forearm vascular resistance to fall in the cool but had no effect in the warm environment. Venous distensibility (increase in venous volume per 30-mmHg increase in venous pressure) was twice as great in the warm as in the cool environment (3.90 ± 0.27 vs. 1.88 ± 0.23 ml/100 cc arm). However, the venodilatory effect of nitroglycerin was similar in the cool and warm environments (0.79 ± 0.10 vs. 0.67 ± 0.13 ml/100 cc arm, respectively). Arterioles are not dilated by nitroglycerin in the warmer environment, but the venodilatory effect of nitroglycerin is quantitatively similar in the two environments.