CSF CONCENTRATION GRADIENTS OF MONOAMINE METABOLITES IN PATIENTS WITHHYDROCEPHALUS

Concentration gradients of homovanillic acid (HVA), 5-hydroxyindoleace tic acid (5-HIAA), and 3-methoxy-4-hydroxyphenylglycol (MHPG), were as sessed in 762 successive CSF fractions (2 ml lumbar CSF) from 15 patie nts with the adult hydrocephalus syndrome (AHS) and 11 patients with h ydrocephalus of other causes (mixed group). A mean volume of 49.6 (SD 11.8) ml CSF was removed in the AHS group and 56.4 (10.2) ml in the mi xed group. The CSF was collected with a specially designed carousel fr action collector and the corresponding CSF dynamics were continuously registered by a constant pressure CSF infusion method. Pronounced grad ients in CSF HVA and CSF 5-HIAA were seen in both patient groups in th e first 25 ml of CSF removed. The concentration curves levelled off, d espite the removal of larger amounts of CSF and stabilised at about tw ice the initial concentrations. This phenomenon has not been described before. Concentrations of HVA and 5-HIAA in the first CSF fraction co rrelated strongly with concentrations in fractions up to about 40 ml. A positive correlation between the first fraction of CSF HVA and CSF 5 -HIAA concentrations and CSF outflow conductance was found in the AHS group. There was no gradient in MHPG. It is suggested that the rostroc audal gradients in CSF HVA and 5-HIAA may be explained by a downward f low of CSF along the spinal cord with absorption of metabolites occurr ing during passage. Mixing of CSF from different CSF compartments, ext raventricular production sites of CSF, clearance of metabolites to ven ous blood or extracellular fluid, and CSF outflow conductance are prob ably important determinants of the plateau phase in patients with hydr ocephalus. It is concluded that lumbar CSF Bees not exclusively reflec t the concentrations of HVA, 5-HIAA, or MHPG in the ventricles. It sho uld be noted that these results obtained in patients with hydrocephalu s may not be applicable to other groups of patients or normal subjects .