Histamine receptor‐mediated sustained post‐exercise vasodilation in young trained and untrained adults

Histamine‐mediated sustained post‐exercise vasodilation in response to one hour of dynamic knee extension has been established in young, recreationally active adults. Endurance training leads to an increased muscle blood flow from vascular remodeling and enhanced vasodilation during exercise in young adults. However, it is unknown whether endurance exercise training modifies histamine mediated post‐exercise arterial vasodilation in young adults. The purpose of this study was to test the hypothesis that sedentary young adults have similar histamine receptor mediated sustained post‐exercise vasodilator responses compared to endurance trained young adults. A randomized, double‐blind placebo‐controlled crossover study including 6 endurance trained (3F, 3M; ages 18–26) and 5 sedentary (3F, 2M; ages 22–29) adults was completed. Subjects orally consumed either a combined histamine H 1 and H 2 receptor blockade with 540 mg fexofenadine (Allegra, H 1 receptor blocker) and 300mg ranitidine (Zantac, H 2 receptor blocker), or placebo pills containing only the inactive ingredients of fexofenadine and ranitidine. Femoral vascular conductance was calculated by dividing femoral artery blood flow obtained using duplex Doppler ultrasound by brachial artery blood pressure measurements. Pre‐exercise measurements were made every 30 minutes for 90 minutes, while post‐exercise measurements were made every 30 minutes for 2 hours. After 90 minutes of supine rest, subjects completed 1 hour of dynamic knee extension exercise at 60% of maximal work rate. Subject demographics and baseline variables were analyzed using independent t‐tests. Post‐exercise differences between groups in the blockade and placebo conditions were analyzed using a mixed effect model ANOVA with repeated measures. All values are reported as mean ± SE. The endurance trained group had higher self‐reported weekly physical activity compared to the sedentary group (73.03 ± 10.5 vs. 27.4 ± 9.5 METhr/wk, p=0.012). Pre‐exercise mean arterial pressure was not different between the two groups in either placebo or blockade conditions (trained placebo: 83±2, trained blockade: 84±2, sedentary placebo: 84±1, sedentary blockade: 86±3 mmHg, p=0.745). Baseline femoral vascular conductance was not different between groups in either placebo or blockade condition (p=0.905). At 60 minutes post exercise, the change in femoral vascular conductance from baseline was not different between the groups for either placebo or blockade condition, although there was a trend towards drug effect of histamine receptor blockade (p=0.192). These preliminary results suggest that there is no difference in post‐exercise femoral vascular conductance between endurance trained and sedentary young adults. Support or Funding Information Support provided by NIH grant HL115027