Plasma catecholamine and parathyroid hormone responses in cattle during treadmill exercise at simulated high altitude.

When steers were exposed to treadmill exercise at a simulated altitude of 3500 m, plasma concentrations of epinephrine and norepinephrine as well as of parathyroid hormone increased within minutes. Heart rate, erythrocyte number and plasma lactic acid level rose at the same time, whereas plasma free fatty acids showed a later increase. It is concluded, that the elevated parathyroid hormone levels were probably caused by sympathetic stimulation.