Effect of heat stress on plasma levels of arginine vasotocin and mesotocin in domestic fowl (Gallus domesticus).

1. The effect of an acute heat stress on plasma arginine vasotocin (AVT) and mesotocin (MT) levels were determined in non-heat-acclimated domestic fowl. 2. Heat increased (P less than 0.05) AVT and decreased MT (P less than 0.05) levels but had no affect on plasma osmolality. Changes in MT were correlated with body temperature (-0.40) and blood pCO2 (0.32). However, changes in AVT were not correlated with any physiological variable, including MT. 3. During thermoneutral recovery, with the exception of hematocrit which remained lower (P less than 0.05), all monitored variables returned to values which were not different (P greater than 0.05) from those observed prior to heat stress. 4. These results indicate that in non-heat-acclimated birds, acute heat stress elevated plasma AVT and suppressed the release of MT and that changes in these hormones occurred independent of any change in plasma osmolality.