Cardiovascular and hormonal responses to swimming and running in the rat.

Hemodynamic and hormonal responses were studied during swimming (SW) and running (R) and in cage-confined (C) female Wistar rats at base line and 4 and 8 wk of training. Myocardial tissue levels of norepinephrine (NE) and epinephrine (EPI) were also measured at the end of 8 wk of training. Mean arterial blood pressure (BP), heart rate (HR), and blood samples for arterial lactate, plasma NE and EPI, and blood gases were obtained at rest and at 20, 40, and 60 min of exercise. After 4 wk of SW, a resting bradycardia was observed, and HR response for the remaining 4 wk was attenuated with SW compared with HR during R. BP and blood gases remained unchanged between the two groups. R resulted in increased arterial lactate concentrations compared with C and SW at base line but was not different from SW at 4 wk. SW elicited higher plasma levels of NE and EPI compared with C at base line and C and R at 4 wk. Myocardial tissue NE and EPI concentrations were markedly increased in both the left and right ventricle of the SW group compared with both R and C. These results indicate that BP and blood gases are not different between chronic R and SW and suggest a possible sympathoadrenal role in the differences observed in cardiac adaptations between R and SW.