EFFECTS OF ACUTE SALT LOADING ON VASOPRESSIN MESSENGER-RNA LEVEL IN THE RAT-BRAIN

To assess the mutual relationship between acute osmotic stimulation an d arginine vasopressin (AVP) gene expression, 2 ml/100 g body weight o f 0.9 M NaCl was intraperitoneally administered into conscious rats. T hey were decapitated to collect blood and brain samples before and 15 min and 1, 3, 6, and 9 h after the injection. The total RNA from the h ypothalamus or whole brain tissue was used to determine AVP mRNA by No rthern blot analyses with a complementary DNA probe. Plasma: AVP and o smolality increased rapidly and transiently 15 min and 1 and 3 h after the injection. AVP mRNA was detected in the hypothalamus but not in t he brain tissue without hypothalamus under basal and stimulated condit ions. Brain AVP mRNA increased 2.2-fold at 3 h and 1.7-fold at 6 h (P < 0.05-0.01). These increases appeared to be due to the appearance of AVP mRNA with the shorter migration in the gel. These results suggest that an acute osmotic challenge increases AVP mRNA with size heterogen eity within the hypothalamohypophysial tract.