Reduction in Plasma Vasopressin Levels of Dehydrated Rats Following Acute Stress

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Abstract
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 significantly reduced pAVP after exposure to ether. One group (180-220 g) showed a decline in pAVP of 27% at 2 min (P < 0.05) and 47% at 5 min (P < 0.001) after stress. In a group of larger animals (350-400 g), pAVP levels were reduced by 55% at 1 min (P < 0.05) and 72% at 2 min (P < 0.01) after ether stress. A 3rd group (250-300 g) also had significantly reduced pAVP values of 57% (P < 0.01) 5 min after ether stress but not at 15 min. Nondehydrated rats which were centifuged 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 centrifuged for 5 min; after 120 min of centrifugation, mean pAVP was reduced by 40% (P < 0.02) when compared to the noncentrifuged controls. In contrast to either ether or acceleration stress, nicotine increased (P < 0.005) pAVP 10 min after injection. Ether or acceleration stress does not evoke an increase in the pAVP levels of rats, and, in dehydrated rats, these stressors will produce a significant decline in pAVP.