Exercise-induced changes in blood ammonia levels in humans

Summary

Five male and two female subjects each performed a maximal aerobic capacity ($\dot V{\text{O}}_{{\text{2 max}}}$) test, and two to four submaximal aerobic exercise bouts (requiring approximately 50 and 80% of the individual's measured $\dot V{\text{O}}_{{\text{2 max}}}$) on a motor-driven treadmill. Pre-exercise resting oxygen uptakes ($\dot V{\text{O}}_{\text{2}}$) and heart rates were determined and a venous blood sample drawn prior to each work session. These same measurements were repeated at 4, 15, 30, and 45 min of the resting recovery period that followed each exercise experiment. Additionally, at the 30th min of each 45-min submaximal exercise, another peripheral venous blood sample was drawn following determination of $\dot V{\text{O}}_{\text{2}}$ and heart rate. In all blood samples, the hematocrit and concentrations of ammonia, lactate, pyruvate, glucose, hemoglobin, and total plasma proteins were measured.

A significant exponential relationship was observed betwen blood ammonia levels and $\dot V{\text{O}}_{\text{2}}$ for all sample periods (pre-exercise rest, exercise, and post-exercise recovery). Peripheral venous blood ammonia levels were significantly correlated with levels of pyruvate and lactate, as these latter substrates exhibited a similar exponential relationship with $\dot V{\text{O}}_{\text{2}}$ as was observed with ammonia.