Surface pH responses of muscles of different fiber-type composition to catecholamines

Catecholamines were infused intravenously for 45 min into pentobarbital sodium-anesthetized rabbits. Physiologically low-dose epinephrine (0.125 μg.min^-1.kg^-1) decreased medial gastrocnemius (MG) surface pH (SpH) 0.16 ± 0.03 (SD) (P < 0.001) to a low of 7.25 ± 0.11 and soleus (S) SpH 0.09 ± 0.04 (P < 0.01) to a low of 7.33 ± 0.08 without changing blood pressure significantly. Surface temperature measurements suggested a statistically insignificant small increase in local blood flow in both muscles. With 1.25 μg.min^-1.kg^-1 epinephrine, MG SpH decreased 0.22 ± 0.05 (P < 0.001) to a low of 7.17 ± 0.06 and S SpH decreased 0.10 ± 0.05 (P < 0.02) to a low of 7.26 ± 0.04. The MG SpH decrease exceeded the S SpH decrease in each experiment for both epinephrine infusion levels, and the incremental difference was significantly greater (P < 0.02) with the higher dose, demonstrating a dose-response effect more pronounced for glycolytic compared with oxidative fibers. Norepinephrine infusions of 1.25 and 2.5 μg.min^-1.kg^-1 did not change SpH of either muscle significantly, despite increases in blood pressure of 10 ± 3 (P < 0.002) and 19 ± 10 mmHg (P < 0.02), respectively.