Effect of hydralazine-induced hypotension on glutamate, gamma-aminobutyric acid and some other amino acid levels in medullary regions of the rat.

Concentrations of glutamate, gamma-aminobutyric acid (GABA), glycine, beta-alanine and taurine were measured in microdissected areas of the rostral ventrolateral medulla (RVL), nucleus tractus solitarii (NTS) and caudal ventrolateral medulla (CVL) of the rat, and the effects of hydralazine-induced hypotension on the concentrations of amino acids were examined. All five amino acids were ubiquitously present in these brainstem regions. Hydralazine-induced hypotension increased glutamate levels in the NTS and CVL regions, but decreased GABA levels in all the regions studied. The level of glycine was decreased in the RVL region after hydralazine. Hydralazine decreased beta-alanine levels in the NTS and CVL regions. Electrical stimulation of slices containing the RVL region decreased glutamate levels but increased GABA levels in tissues. These results are compatible with the hypothesis that glutamate and GABA systems in these brainstem areas are related to blood pressure regulation.