Exercise-induced Elevations in Skeletal Muscle Histamine Contributes to Increased Post- exercise Capillary Permeability
Chaucie Edwards
Faculty Mentor(s): John Halliwill & Matthew Ely
Oral Session 4 S
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/H2 receptor 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.