Effects of histamine-receptor antagonism on leg blood flow during exercise.

: Histamine mediates vasodilation during inflammatory and immune responses as well as following endurance exercise. During exercise, intramuscular histamine concentration increases and its production appears related to exercise intensity and duration. However, whether histamine contributes to exercise hyperemia and promotes exercise blood flow in an intensity or duration dependent pattern is unknown. The purpose of this study was to compare leg blood flow across a range of exercise intensities, before and after prolonged exercise, with and without histamine-receptor antagonism. It was hypothesized that combined oral histamine H1/H2-receptor antagonism would decrease leg blood flow and the effect would be greater at higher intensities and following prolonged exercise. Sixteen (7F, 9M) volunteers performed single-leg knee-extension exercise after consuming either Placebo or combined histamine H1/H2-receptor antagonists (Blockade). Exercise consisted of two graded protocols at 20, 40, 60, and 80% of peak power, separated by 60 min of knee-extension exercise at 60% of peak power. Femoral artery blood flow was measured by ultrasonography. Femoral artery blood flow increased with exercise intensity up to 2660±97 ml·min-1 at 80% of peak power during Placebo (P<0.05). Blood flow was further elevated with Blockade to 2836±124 ml·min-1 (P<0.05) at 80% peak power (9.1 ± 4.8% higher than Placebo). These patterns were not affected by prolonged exercise (P=0.13). On average, femoral blood flow during prolonged exercise was 12.7± 2.8% higher with Blockade versus Placebo (P<0.05). Contrary to the hypothesis, these results suggest that histamine-receptor antagonism during exercise, regardless of intensity or duration, increases leg blood flow measured by ultrasonography.