Metabolite-detecting and adrenergic gene expression after 40K time trial performance during thermoneutral and heat-stressed conditions

Strenuous exercise may be limited by metabolite detecting receptors on Group IV afferents which heat stress may exacerbate. This study compared mRNA quantities after prolonged intense exercise during thermoneutral (NT) and heat-stress (HT) conditions on objective markers related to fatigue. Ten cyclists (33.2 ± 3.0 yr, 57.2 ± 1.1 mL/kg/min) performed two 40k time trials; NT (21 C, 10% humidity (RH), temp change (CT) 1.93 C) and HT (35 C, 30% RH, CT 2.10 C). Blood was drawn at baseline, 0.5, 8, 24, and 48 hr after exercise. Leukocytes were separated for qPCR analysis of 5 metabolite detecting receptors (ASIC1, ASIC3, P2X4, TRPV1, TRPV4) and 3 adrenergic receptors (α2a, β1, and β2). Lactates were taken 1 and 5 min post-ex. Power and post-ex lactates were lower and exercise time was longer for HT vs NT (p<.001). After both trials, decreases in ASIC3 and TRPV1 were seen (0.5 and 8 hr, p<.05), with larger decreases after NT (p<.05). Post-ex ASIC3 and TRPV1 were related to 5 min post-ex lactate (r=-.50 and -.60, p<.01). ASIC1 decreased after NT (0.5, 8, and 48 hr, p<.05). P2X4 decreased after both trials (0.5 hr). TRPV4 decreased after NT (0.5 hr, p<.05) and HT (8 hr, p<.001). α2a increased at 0.5 hr after HT and β2 decreased 0.5 hr after NT. Post-ex decreases in metabolite detecting genes may represent downregulation of afferent signaling to reduce fatigue sensations. HT produced smaller changes in post-ex ASIC1, ASIC3 and TRPV1 expression.