Neuropharmacology of delta-aminolaevulinic acid--I. Effect of acute administration in rodents.

Delta-aminolaevulinic acid (ALA) is suspected of being responsible for the neuropsychiatric symptoms of acute porphyria. The object of this study was to examine the effects of ALA in vivo on a range of behavioural and physiological functions which are known to be affected in the acute porphyric attack. Aminolaevulinic acid was administered by intraperitoneal or subcutaneous injection to mice in doses up to 1000 mg/kg and effects on nociception (hot-plate and abdominal constriction tests), CNS excitability (pentobarbitone sleep-time and pentylenetetrazole-induced seizures), motor co-ordination and grip (rotating rod test) were studied. Rats were given intravenous injections or infusions of ALA of up to 24 mg and changes in blood pressure, heart rate and ED50 for noradrenaline, acetylcholine and isoprenaline examined. No statistically significant effects were noted, using buffered solutions of ALA (pH 7.0-7.4). However, unbuffered solutions of ALA caused significant bradycardia and hypotension. These results do not support the hypothesis that ALA has significant acute neuropharmacological activity in vivo when the blood-brain barrier is intact.