CHANGES IN AMINO-ACID LEVELS IN RAT PLASMA, CISTERNAL CEREBROSPINAL-FLUID, AND BRAIN-TISSUE INDUCED BY INTRAVENOUSLY INFUSED ARGININE-VASOPRESSIN

Circulating arginine vasopressin (AVP) is known to reduce the blood-to -brain transfer of large neutral amino acids (AA). As a first step to examine whether the reduced uptake by brain endothelial cells is refle cted in changes in large neutral amino acid levels of the extracellula r fluid environment of cells within the nervous tissue, we measured th e concentrations of amino acids in plasma, cerebrospinal fluid (CSF), and hippocampal tissue of rats before and after infusion of AVP (34 an d 68 mg/min/kg, respectively) over the time period of 60 min. AA level s changed in all compartments investigated during both saline and AVP infusions. Whereas in the saline infused controls changes in CSF AA le vels paralleled those in plasma, this correlation was abolished by rai sing AVP concentrations. The effect of AVP was found to be i) dependen t on the AA, ii) different with respect to direction and iii) magnitud e of changes in AA levels, and iv) in some cases dose dependent. In su mmary, AVP infusion increased plasma levels of 10 AA, but decreased al l 15 AA measured by some 30% in CSF. In contrast to CSF, levels of AA were slightly enhanced in the hippocampal tissue. The results are not solely explicable by a reduced blood-to-brain transfer of AA. We concl ude that further mechanisms by which AVP affects the availability of A A to the brain may exist. The physiological significance of the findin gs might be related to brain osmoregulation, especially in situations of stress.