Reduction in plasma vasopressin levels of dehydrated rats following acute stress.

The development of a sensitive radioimmunoassay for plasma arginine vasopressin (pAVP) is described. Using this assay, the levels of vasopressin were determined in the plasma of nondehydrated and dehydrated rats after exposure to ether or acceleration stress. Plasma AVP was also determined in rats following nicotine administration. Nondehydrated rats showed no significant changes in pAVP 1, 2, 5, or 15 min after exposure to ether for 1 min. Dehydrated rats, on the other hand, had significantly reduced pAVP after exposure to ether. One group (180-220 g) showed a decline in pAVP of 27% at 2 min (P less than 0.05) and and 47% at 5 min (P less than 0.001) after stress. In a group of larger animals (350-400 g), pAVP levels were reduced by 55% at 1 min (P less than 0.05) and 72% at 2 min (P less than 0.01) after ether stress. A third group (250-300 g) also had significantly reduced pAVP values of 57% (P less than 0.01) 5 min after ether stress but not at 15 min. Nondehydrated rats which were centriguated at -4.1 Gx for 5, 15 or 120 min showed no significant alterations in pAVP. No decrease in pAVP was observed in dehydrated rats centrifugated for 5 min; after 120 min of centrifugation, mean pAVP was reduced by 40% (P less than 0.02) when compared to be noncentrifugated controls. In contrast to either ether or acceleration stress, nicotine provoked a marked rise (P less than 0.005) in pAVP 10 min after injection. From these results it was concluded that ether or acceleration stress does not evoke an increase in the pAVP levels of rats, and furthermore, in dehydrated rats, these stressors will produce a significant decline in pAVP.