Metabolism of 125Iodochloroxyquinoline in Man

Abstract

Summary 126I-labelled iodochloroxyquinoline (125ICOQ, Vioform®, CIBA) was given orally in tracer doses to 3 euthyroid and 3 hyperthyroid subjects. Samples of plasma, urine and faeces were closely analysed.The formation of 3 metabolites was demonstrated: a) a glucosiduronate (125ICOQ-gluc), b) a sulphate ester (125ICOQ-sulph) and c) an unidentified compound (125ICOQ-X) which may possibly be a dihydroxy compound.The main compound in urine was 125ICOQ-gluc. The proportion of this compound increased with time, while that of 125ICOQ and 125ICOQ-X decreased. The percentage 125ICOQ-sulph remained unchanged. The conjugates were also found in plasma but the radioactivity was mainly distributed between 125ICOQ and 125ICOQ-X. The protein-bound radioactivity in the plasma was located to albumin. More than 90 per cent of the plasma radioactivity could be removed with 3 butanol extractions. A small decrease in butanol extractability with time was noted.Comparison of the ratio between water-soluble and butanol soluble compounds in the plasma dialysate and in the corresponding urine revealed a similar ratio, indicating a similar renal clearance for all the substances. The decrease of 125ICOQ and 125ICOQ-X in the urine with time may partly be due to a firmer binding of these compounds to the plasma proteins. The spontaneous increase in the excretion of radioactivity in the urine (9) is probably due to an adaptation of the liver enzymes for forming conjugates.Faeces contained only minute amounts of the conjugates which, however, indicated the existence of an enterohepatic circulation for 125ICOQ. The main faecal metabolites were original 125ICOQ and 125ICOQ-X. The site of formation of 125ICOQ-X is assumed to be the liver or gastrointestinal tract.In none of the chromatograms of plasma, urine or faeces could any radioactive iodide or thyroidal hormones be demonstrated.