Postmortem increase of GABA levels in peripheral rat tissues: prevention by 3-mercapto-propionic acid.

The postmortem alteration of gamma-aminobutyric acid (GABA) levels was examined in the rat brain, kidney, ovary and oviduct up to 30 minutes after decapitation. GABA concentrations progressively increased with time in each organ. At 30 minutes, the following elevations were found in percent: brain 65, kidney 75, ovary 38 and oviduct 32. Pretreatment with 3-mercapto-propionic acid (3-MPA, 1.2 mmol/kg i.v.), 2.5 minutes prior to killing, completely prevented the postmortem increase of GABA levels in the brain, the ovary and the oviduct, but only slightly reduced the elevation of renal GABA content. In ex vivo experiments, the same treatment reduced with about 50 percent the activity of L-glutamate decarboxylase (GAD) in the brain and the oviduct, but failed to influence the enzyme activity in the kidney. In vitro, 3-MPA was far more potent in inhibiting cerebral and tubal than renal GAD. The present findings provide evidence for the ability of the 3-MPA treatment used, to prevent the postmortem increase of not only cerebral, but also oviductal and ovarian GABA levels. This procedure, however, proved to be inadequate for fixation of GABA concentration in the kidney.