Plasma catecholamine and cardiovascular responses of trained and untrained men exposed to physical and psychological stressors

The plasma catecholamine and cardiovascular responses of trained(T) and untrained(UT) males were measured during exposure to several physical and psychological laboratory stressors. Sixteen subjects (8 T and 8 UT) were exposed to an orthostatic hypotension test, a cold-pressor test, an isometric hand grip test, a reaction time-avoidance of shock task, and a reaction time-appetitive task. Five to 10 minute rest periods separated the tasks. The Ss were randomly assigned to a test order based on a latin square design. During the experimental protocol, heart rate(HR), systolic blood pressure(SBP), diastolic blood pressure(DBF), and plasma epinephrine(E) and norepinephrine(NE) concentrations were measured at specified time intervals. Maximal oxygen uptake was 70.5 + 0.8 and 45.5 + 1.1 ml(kg.min)-1 + SE for the T and UT groups, respectively (p<0.0001). Multiple t-tests for independent means were used to test for differences between the groups.

Although there were no significant differences between groups for any of the dependent variables for any test except mean resting HR (p<0.05), it was interesting to note that plasma NE concentrations were consistently higher in the trained group for each task. These results suggest that a form of adaptation evidenced in a chronically trained population may involve increased secretion of NE in response to novel stressors, or that adaptation to exercise is specific and that there is no SNS cross adaptation to these laboratory stressors.