C.K. Edwards, M.R. Ely, D.C. Sieck, J.E. Mangum, E.A. Larson, J.R. Halliwill FACSM.

University of Oregon. Eugene, OR

Histamine, an endogenously released molecule in immune and inflammatory responses increases local vasodilation, blood flow, and capillary permeability. During exercise, histamine is produced within exercising muscle and contributes to an elevated post-exercise blood flow. The histamine-induced post-exercise vasodilation is contained within previously exercised muscle as histamine concentrations are not elevated in non-exercised muscle (i.e. arms during leg exercise). It is unknown if intramuscular histamine also contributes to elevate capillary permeability following exercise. PURPOSE: To compare capillary permeability of the leg before and after prolonged unilateral knee-extension exercise under normal conditions and when histaminergic signaling is blocked. It was hypothesized that H1/H2receptor antihistamines would decrease capillary permeability following exercise in an exercised leg but not in a resting leg. METHODS: Six (2F) volunteers performed 60 min of unilateral knee-extension exercise at 60% of peak power after consuming either Placebo or histamine (H1/H2) receptor antagonists (Blockade). A capillary filtration coefficient (CFC) reflecting the rate of change in limb girth per rise in venous pressure was calculated using venous occlusion plethysmography. A CFC was calculated prior to (PRE) and following (POST) exercise in both the exercised leg (EL) and the resting leg (RL). Data were analyzed with a 3-way RM ANOVA and presented as Means±SEM. RESULTS: On average, CFC increased 161±90% (PRE: 2.5±1.0 to POST: 6.6±2.3 μg·100g-1·min-1·mmHg-1) in the EL and 38±31% (PRE: 4.8 to POST: 6.5 μg·100g-1·min-1·mmHg-1) in the RL during Placebo. Blockade attenuated the exercise-induced rise in CFC in the EL to 13±41% (PRE = 4.3±1.3 to POST = 4.9±1.8 μg·100g-1·min-1·mmHg-1) and in the RL 2±45% (PRE: 3.8±1.4 to POST: 3.8±1.7 μg·100g-1·min-1·mmHg-1). Due to the high variability in the measures there was a trend for CFC to increase with exercise (P=0.161), for Blockade to attenuate the rise in CFC (P=0.363), and for a leg by drug interaction (P=0.289). CONCLUSION: These initial data suggest that exercise-induced histamine production contributes to the elevated CFC within exercised limbs.

Support provided by: ACSM NW Student Research Award; O’Day Fellowship; Carol Carver Pay-it-Forward Thesis Grant

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