Neurohumoral and cardiopulmonary response to sustained submaximal exercise in the dog

Neurohumoral, cardiovascular, and respiratory parameters were evaluated during sustained submaximal exercise (3.2 km/h, 15° elevation) in normal adult mongrel dogs. At the level of activity achieved (fivefold elevation of total body O₂ consumption and threefold elevation of cardiac output), significant (P < 0.05) increases in plasma norepinephrine and epinephrine concentration (from 150 ± 23 to 341 ± 35 and from 127 ± 27 to 222 ± 31 pg/ml, respectively) were present, as well as smaller but significant increases in plasma renin activity and plasma aldosterone concentration (from 2.2 ± 0.3 to 3.1 ± 0.6 ng·ml^-1·h^-1 and from 98 ± 8 to 130 ± 6 pg/ml, respectively). Plasma arginine vasopressin increased variably and insignificantly. The cardiovascular response (heart rate, systemic arterial and pulmonary arterial pressures, left ventricular filling pressure, and calculated total peripheral and pulmonary arteriolar resistance) closely paralleled that of human subjects. Increased hemoglobin concentration was induced by exercise in the dogs. The ventilatory response of the animals was characterized by respiratory alkalosis. These data suggest similarities between canine and human subjects in norepinephrine, plasma renin activity, and plasma aldosterone responses to submaximal exercise. Apparent species differences during submaximal exertion include greater alterations of plasma epinephrine concentration and a respiratory alkalosis in dogs.