PLASMA ATRIAL-NATRIURETIC-PEPTIDE IN STANDARD-BRED AND FINNHORSE TROTTERS DURING AND AFTER EXERCISE

To study the exercise-induced changes in atrial natriuretic peptide (A NP), a hormone with cardiovascular and renal effects, an incremental s ubmaximal exercise test on a highspeed treadmill was carried out with Standardbred and Finnhorse trotters, the former bred for speed and the latter originally for heavy work. Standardbreds performed the 2 min e xercise intervals at speeds of 6, 7, 8, 9 m s(-1) and Finnhorses, acco rding to their training status, at 5, 6, 7, 8 m s(-1), 4, 5, 6, 7 m s( -1) or 5, 6, 7 m s(-1). Steady-state heart rate (HR) was reached withi n each 2 min interval. The increase in HR was linear and proportional to work intensity and physical condition and it peaked, average 204 be ats min(-1), during the last speed of the treadmill. Plasma ANP increa sed significantly and equally, by 27 +/- 4 pg mL(-1), in both breeds a nd peaked at 5 min post-exercise. The rise in RNP during exercise show ed good linearity with HR and increasing work intensity. The decrease of ANP after exercise was slow, which may be connected to the regulati on of water and electrolytes. interbreed differences in plasma ANP wer e not observed. The results suggest a role of ANP in cardiovascular co ntrol and fluid balance during and after exercise. In addition to othe r possible releasing factors during exercise, the increase in HR expla ins about 40% of the variability in the plasma ANP values.