PLASMATIC TRYPTOPHAN BIOAVAILABILITY IN C HRONIC URTICARIA

Objectives. Chronic idiopathic urticaria is known to have psychogenic component with a triggering or favoring effect. Different tests or eva luation scales have been unable to identify a specific psychological p rofile. Erythrocyte-specific membrane transport of tryptophan (TRP), t he main plasma precursor of cerebral serotonin synthesis, controls; by a erythrocyte-specific storage and release mechanism, circulating TRP homeostasis. Bioavailability of circulating TRP is a factor controlli ng serotonin synthesis in the brain. An evaluation of the rate of TRP transfer could be a biochemical approach to chronic urticaria more inf ormative than psychological tests. Patients and methods. A kinetic stu dy of L-TRP influx into circulating erythrocytes was conducted in 17 p atients with chronic urticaria with no detectable cause and in 35 heal thy controls. Blood samples were marked with H-3-TRP. Maximum L-TRP-sp ecific influx (V-max) was expressed in mu mol/cell/min. The urticaria patients also underwent psychological testing to determine anxiety and depression scores using standardized scales (Hamilton). Results. Mean V-max was not significantly difference between the two groups. V-max values were quite similar in all the control subjects but showed wide dispersion in the urticaria group. Three subgroups were found in the u rticaria patients depending on V-max those with V-max equivalent to co ntrol levels (+/- 2 SD), those with V-max less then 2 SD (29% of the p atients) and those with V-max greater than 2 SD of control levels (23% of the patients). Thus more than 50% of the urticaria patients had pe rturbed erythrocyte-specific L-TRP influx. The anxiety and depression scores obtained from the psychological evaluation were not correlated with V-max. Discussion. Erythrocyte-specific TRP membrane transport, e valuated by V-max. Would not appear to be perturbed in chronic urticar ia. Even though the urticaria patients could be divided into three gro ups according to their V-max, the mean value was not significantly dif ferent from that in controls. These findings do not allow a conclusion concerning a perturbation of bioavailability of plasmatic TRP and any possible central serotoninergic dysfunction in chronic urticaria.