Hypohydration increases the plasma catecholamine response to moderate exercise in the dog (Canis).

1. The effects of hypohydration produced by 48 hr water deprivation were examined in dogs during moderate treadmill exercise at an ambient temperature (Ta) of 21 degrees C. 2. Hypohydration caused a significant elevation in plasma levels of adrenaline (A), proteins (pp) and osmolality (pOsm). 3. During 1 hr of running, plasma concentrations of adrenaline (A) and noradrenaline (NA) rose significantly, whilst no change in these hormones occurred in dogs hydrated ad libitum. 4. The results suggest that hypovolemia in the dog may be a sufficient stimulus to intensify the sympatho-adrenal response to moderate exercise performed at a room Ta.