Metabolic clearance and production of diiodotyrosine in healthy man.

Metabolic clearance rate (MCR) and daily production rate (PR) of diiodotyrosine (DIT) were estimated using a constant infusion technique of trace amounts of [125-I]-DIT followed by chromatographical isolation of tracer. Median DIT MCR was in eight healthy subjects estimated to 162 l/day x 70 kg (range 135-242), whereas PR was 52 nmol/day x 70 kg (range 25-126). The median serum DIT concentration was 0.27 nmol/l (range 0.16-0.62). In five L-thyroxine substituted subjects without endogenous thyroxine (T4) production, serum DIT concentrations were below 0.02 nmol/l, suggesting that more than 94% of daily produced DIT is secreted by the thyroid gland.

Pharmacokinetics and urinary excretion of orally administered diiodotyrosine.

Serum levels of diiodotyrosine (DIT) and urinary excretion rates of DIT and iodine were measured in 10 normal subjects after oral administration of 1.57 mumol of DIT corresponding to 400 micrograms of iodine. Serum DIT concentrations rose promptly from a mean endogenous basal level of 0.23 nmol/l to maximum values between 6.0 and 20 nmol/l within 30 min to 1 h after DIT ingestion. Decreasing DIT levels were found in all subjects 2 h after DIT intake. Urinary excretion of intact DIT was low, being less than 1% of the administered dose of exogenous DIT within 2 days. In contrast, 52% of the iodine administered in the form of DIT was excreted in the urine in the same time interval. The rapid absorption of DIT from the gastrointestinal tract combined with rapid and almost complete metabolic degradation by deiodination make orally applied DIT seem a suitable iodine carrier compound for therapeutic purposes.