BEETURIA AND THE BIOLOGICAL FATE OF BEETROOT PIGMENTS

Beeturia, the passage of pink or red urine after the ingestion of beet root, is said to occur in 10-14% of the population, and is more common in iron deficiency and malabsorption. A specific HPLC assay for betac yanins, the red beetroot pigments, in biological fluids was developed to study the prevalence of this apparent polymorphism in humans, and t o investigate its basis in rats. Two major peaks were observed in chro matograms of extracts of unpickled beetroot. They had identical UV abs orption spectra (lambda(max) = 535 nm) by diode array analysis, and ma ss spectrometry indicated that one (betacyanin 1) was betanin or its e pimer and the other (betacyanin 2) a dissacharide of betacyanin 1. In a population of 100 normal subjects the 0-8 h urinary recoveries after an oral dose of 60 mg beetroot extract were 0.06-0.54% for betacyanin 1 and 0.01-0.6% for betacyanin 2. The distributions of these data wer e skewed but not clearly bimodal by visual inspection or by kernel den sity analysis. Four subjects produced visibly red urine and had betacy anin recoveries at the upper end of the population range. Studies usin g in situ isolated perfused rat jejunum and liver preparations indicat ed a negligible absorption of the pigments after 1 h and no detectable metabolism or biliary secretion. Intact anaesthetized rats given i.v. bolus doses of beetroot extract cleared both betacyanins from plasma at the rate of 3.3 +/- 0.9 (SD) ml min-1 (n = 5). The total urinary re covery of both pigments amounted to 80% of the dose, and their renal c learances approached their plasma clearances. These data suggest that beeturia does not arise from deficiencies in hepatic metabolism or ren al excretion of betacyanins. After oral administration of beetroot ext ract to rats the betacyanin content of the stomach decreased rapidly w ith time but neither the intestines nor the bile duct were stained vis ibly red. These findings together with those showing instability of th e betacyanins in acid conditions suggest that variability in the biolo gical fate of beetroot pigments may be determined largely by gastric p H and emptying rate.