Fig. 4.

Effects of hyperoxia, hyperoxic exercise, and NTP infusion on vasoconstrictor responsiveness to endogenous norepinephrine release via tyramine. The change (Δ) in forearm blood flow (FBF) (A) and forearm vascular conductance (FVC) (B) (% decrease) was blunted with exercise compared with rest (normoxia and hyperoxia). The Δ in FBF and FVC was slightly greater during hyperoxic exercise than during normoxic exercise. The Δ in FBF and FVC during NTP infusion was greater than both normoxic and hyperoxic exercise. *P < 0.01 vs. rest. †P < 0.05 vs. normoxic exercise. ‡P <0.01 vs. normoxic and hyperoxic exercise.