Effect of cigarette smoking on human precapillary sphincters.

1. Capillary filtration coefficient of human calf was measured by pressure plethysmography before and after cigarette smoking, which is known to release noradrenaline from nerve terminals of sympathetic vasoconstrictors. Calf blood flow and venous pressure-volume curves of the calf were also obtained before and after smoking.2. Capillary filtration coefficient decreased by 19% when cigarette smoke was inhaled deeply at 30 s intervals for 12-15 min, indicating the closure of precapillary sphincters.3. Calf blood flow decreased by 31% after smoking, indicating that arterioles were constricted. The degree of arteriolar constriction, however, was not strong enough to lessen the capillary hydrostatic pressure, since the absorption of tissue fluid into capillary blood vessels did not occur.4. The venous system seemed little affected by cigarette smoking, since venous pressure-volume curves were unaltered.