Chronic exposure to swim stress (i.e., training) is associated with functional adaptations of the cardiovascular system. On the other hand, repeated exposure to tail shock, an emotional stress, often results in deleterious changes in resting blood pressure and myocardial pathology. We hypothesized that the pathological adaptation following chronic exposure to tail shock was associated with a larger acute physiological response compared with swim stress. Therefore, acute responses to swim and shock stress were compared. A second concern of this study examined the extent to which adaptation to swim training influences responses to predictable tail shock stress. The cardiovascular and sympathoadrenal responses to swim stress, using 1% body wt attached to the tail, were compared with predictable tail shock (0.2-0.4 mA intensity, 1-s duration, 1/min) in two groups of Long-Evans male rats. In the first, 11 rats were studied following 5-7 wk of swim training, consisting of daily 1-h sessions of swimming with 2% body wt attached to their tails. They were compared with an age-matched nontrained (NT) group (n = 8). During swimming, the trained animals showed significantly lower heart rate (387 +/- 10 vs. 449 +/- 18 beats/min) and significantly lower lactate (0.9 +/- 0.09 vs. 2.0 +/- 0.24 mmol/l), epinephrine (332 +/- 57 vs. 739 pg/ml), and corticosterone (32 +/- 10 vs. 62 +/- 9 micrograms/dl) responses. Systolic and diastolic blood pressures were elevated in swim stress by the same degree in trained (167/110 mmHg) and NT (177/116 mmHg) rats.(ABSTRACT TRUNCATED AT 250 WORDS)