ABSENCE OF CIRCADIAN VARIATIONS IN URINARY PORPHYRIN EXCRETION IN NORMAL SUBJECTS

The hypothesis that urinary porphyrins could be excreted in a circadia n rhythm was examined. A group of 20 healthy subjects, 10 males and 10 females, aged 20-40 years, were used in this study. Urine was collect ed at 4-hr intervals over three 24-hr periods. Median porphyrin concen trations (mu gl(-1) or mu g g(-1) of creatinine) were similar in the s ix groups, but significant differences were observed in that excreted. Highest porphyrin excretion was detected in the afternoon (12.00-16.0 0 hr) and, in the evening (16.00-20.00 hr). pH values were also increa sed at evening but did not correlate with porphyrin excretion. Despite these temporal variations, no cycles indicating circadian periodicity were observed. Therefore, a 24-hr collection of urine is not necessar y for the initial evaluation of porphyrin metabolism.