Control of central release of vasopressin.

A diffuse extrahypophyseal vasopressinergic system has been described in the brain, and vasopressin (AVP) has also been identified in the cerebrospinal fluid (CSF) of several species. Administration of AVP to the central nervous system has been found to influence several brain functions. It has been suggested therefore that this peptide may act as a physiologically significant neuromodulator of the central nervous system functions, including the control of the body fluid homeostasis. However, the mechanisms controlling the central release of AVP are poorly recognized. The purpose of the present investigation was to find out whether the release of AVP into the CSF is controlled by volume and osmotic stimuli and whether it may be relevant to the control of water intake. The experiments were performed on conscious dogs chronically implanted with a device enabling the withdrawal of CSF from the anterior part of the third ventricle which is situated in the vicinity of abundant vasopressinergic fibers. AVP measured by radio-immunoassay and osmolality were determined in blood and CSF samples taken simultaneously. 24 h dehydration caused a significant elevation of plasma (Posm) and CSF (CSFosm) osmolalities as well as of plasma (PAVP) and of CSF (CSFAVP) AVP concentrations. During rehydration total water intake (TWI) X kg-1 b.w. was significantly correlated with Posm and PAVP as well as with CSFosm and CSFAVP prior to drinking. Rehydration caused Posm, PAVP, CSFosm and CSFAVP to decrease significantly within 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)