Effects of osmotic stimuli on vasopressin levels in the CSF of rats.

Arginine-vasopressin (AVP) levels and osmolality were measured in the CSF of rats during 5 days of osmotic stimulation. Dehydration increased AVP levels about 3-fold but did not affect the circadian rhythm of AVP. During dehydration, AVP levels in CSF increased as osmolality increased. Neither AVP levels nor osmolality changed significantly in the CSF of rats receiving 2% NaCl as drinking water. The increased AVP values in CSF may reflect activated release of AVP in the central nervous system during dehydration. Our data also suggest that the AVP release connected with the regulation of osmotic changes may be separate from the mechanism that regulates the circadian rhythm of AVP in the CSF of rats.