Estimation of levels of serotonin and 5-hydroxyindoles in whole blood by an autoanalytical procedure: observations on the blood-brain barrier.

Abstract— We describe a method for the fluorometric determination of 5-hydroxyindoles in the physiological range of 0.010–1.30 μg/ml of whole blood by means of an autoanalytical procedure. Serotonin is dialysed free from haemolysed blood constituents and a complex between 5-HT and o-phthaldialdehyde is formed in the dialysand to provide a considerable increase over the native fluorescence of 5-HT in strong acid. The method has been evaluated and considered to be accurate for the continuous monitoring of levels of 5-HT in whole blood and for the determination of cerebral arteriovenous differences. The range of values for human patients with cerebrovascular disease was 0.09–0.34 μg/ml of whole blood. In experimental studies on the baboon the range was 0.538–1.28 μg/ml. A mean positive cerebral arteriovenous difference for 5-HT (and possibly other 5-hydroxyindoles) of 0.037 μg/ml was measured in 10 baboons. This finding suggests the possibility of physiological movement of 5-HT and 5-hydroxyindoles into brain across the blood-brain barrier.