Nicotinic acid (NA) administration in
Gilbert's syndrome (GS) patients promotes an increment of
bilirubin and of total
iron serum levels, dependent on a defective hepatic
bilitranslocase function and on a haemolytic effect of NA. In
porphyria cutanea tarda (PCT): (1) the effect of
nicotinic acid on bilirubinaemia is superimposable to that in controls; (2) a well documented disturbance of
iron metabolism occurs; (3) but relationship between
bilirubin and
iron under NA load has never been investigated. The administration of 5.9 mumol/kg
body weight of NA to 12 PCT patients, 10 GS subjects and nine healthy volunteers of comparable age resulted in: (1) normal behaviour of
bilirubin parameters in PCT but higher bilirubinaemic values in GS subjects; (2) normal values of serum
iron in GS subjects, but higher baseline values and lower sideraemic effect of
nicotinic acid in PCT patients; (3) a normal NA half-life in PCT and enhanced in GS subjects. These findings confirm a defective
bilirubin uptake and excretion by the liver of GS subjects with a normal
iron metabolism. On the contrary, in our PCT patients a normal clearance of
bilirubin occurs, but a complex disturbance of
iron metabolism is well evident in baseline conditions as well as after NA administration. The latter being probably the consequence of an enhanced excretion of
iron extraproduced by the haemolytic effect of NA.