Journal of Applied Physiology, Vol 61, Issue 6 2012-2017, Copyright © 1986 by American Physiological Society
Effect of methylene blue on cardiac output response to exercise in dogs
N. Imai, J. I. Paley, H. S. Barold and C. S. Liang
To determine whether the increase in cardiac output during mild to moderate
exercise is related to an increase in the tissue redox potential, we
compared the responses of cardiac output, total body oxygen consumption,
and arterial blood lactate-to-pyruvate ratio (a measure of NADH/NAD) to
treadmill exercise between dogs treated with normal saline and those
treated with a hydrogen acceptor, new methylene blue. Normal saline was
infused into the left atrium in the first group of dogs at a rate of 0.38
ml/min throughout the treadmill exercise (2.5 mph and 5.0 mph on a 6%
incline, each for 20 min). In the second group, methylene blue was
administered as a loading dose (4 mg/kg) before exercise, followed by a
continuous infusion (0.15 mg X kg-1 X min-1) throughout exercise. A similar
infusion of methylene blue was given to a third group of dogs without
exercise; it reduced the arterial lactate-to-pyruvate ratio from 6.70 +/-
0.35 to 4.12 +/- 0.27 but had no or little effects on cardiac output, heart
rate, arterial pressure, and left ventricular dP/dt and (dP/dt)/P.
Treadmill exercise doubled cardiac output and increased total body O2
consumption three- to fourfold in the first two groups but increased
arterial blood lactate-to-pyruvate ratio only in group 1 (6.0 +/- 0.54 to
9.97 +/- 0.91). The relationship between cardiac output and total body O2
consumption was unaffected by the simultaneous administration of methylene
blue during exercise. Groups 1 and 2 also did not differ in their heart
rate, left ventricular dP/dt and (dP/dt)/P, and plasma catecholamine
responses to exercise.(ABSTRACT TRUNCATED AT 250 WORDS)
