The effect of intravenous administration of GABA and brain extracts on blood pressure in the rat.

1. A rat bioassay was used to study pressor substances in brain extracts. 2. A compound with pressor activity in pentolinium-treated rats was extracted from brain, purified using Dowex, Sephadex electrophoresis and identified as gamma-aminobutyric acid (GABA) by HPLC and mass spectrometry. 3. Intravenous GABA (1-5 microgram) or brain extracts caused a dose dependent decrease in blood pressure in pentobarbitone-anaesthetized rats. 4. After ganglion blockade with pentolinium (2 mg/kg subcutaneously), GABA or brain extracts cause a dose dependent increase in rat blood pressure. 5. This pressor effect is reduced by alpha- and beta-blockers (intravenous phentolamine, 0.5 mg/kg and propranolol, 0.05 mg/kg). 6. It is concluded that GABA causes a fall in blood pressure by a central mechanism and ganglion blockade unmasks a pressor effect.