A radioimmunoassay for measurement of thyronine and its acetic acid analog in urine.

Abstract

A sensitive and specific RIA has been developed to measure thyronine (To) in urine. The RIA used an anti-To antibody obtained from a rabbit immunized with a L-To-human serum albumin conjugate and [3H]To as the radioligand. The acetic acid analog of To (ToAc), that is the diphenyl structure with an acetic acid side-chain, cross-reacted strongly with the antibody. Relative to To, it cross-reacted 160% in phosphate-buffered saline, pH 7.4, and 100% in 0.075 mol/L barbital buffer, pH 8.6, containing sodium salicylate (final concentration, 8 mg/mL). The latter conditions were employed for the RIA, and the results reported thus reflect the presence of To and/or ToAc. 3-Monoiodothyronine, 3'-monoiodothyronine, 3',5'-diiodothyronine, and 3,5-diiodothyronine cross-reacted with the anti-To antibody 1.9%, 1.7%, 0.3%, and 0.2%, respectively; the cross-reactivity of other To derivatives and tyrosine and its derivatives was less than 0.05%. Urinary To and/or ToAc excretion in 12 normal subjects averaged 16 +/- 2 (+/- SE) micrograms/day (59 +/- 9 nmol/day) or 14 +/- 2 micrograms/g creatinine (5.9 +/- 0.6 nmol/mmol creatinine). Treatment of urine from normal subjects with beta-glucuronidase or sulfatase did not significantly alter the To content. Column and thin layer chromatographic studies revealed that 83% and 61%, respectively (range, 37-100%), of urinary To immunoreactivity was attributable to ToAc. The mean daily excretion of To in 20 patients with nonthyroidal illness [NTI; 22 +/- 4 micrograms/day (82 +/- 17 nmol/day)] was similar to that in normal subjects, but was elevated when expressed as nanomoles per mmol creatinine (20 +/- 2; P less than 0.001), because creatinine excretion was reduced in the NTI patients. The mean daily urinary To excretion in 13 patients with hyperthyroidism due to Graves' disease was slightly elevated [29 +/- 6 micrograms/day (108 +/- 21 nmol/day); P less than 0.1], but was clearly elevated when expressed as nanomoles per mmol creatinine (37 +/- 8; P less than 0.001), again because creatinine excretion was reduced in these patients. The mean urinary To excretion was subnormal in 13 patients with hypothyroidism and was significantly (P less than 0.005) less than that in the NTI patients regardless of the manner in which the results were expressed. Analysis of pronase hydrolysates of thyroid glands obtained at autopsy from euthyroid patients suggested that the To content of the thyroid approximates only 1.2% that of T4, supporting the thesis that prior iodination of tyrosine is critical for the coupling process in the thyroid.(ABSTRACT TRUNCATED AT 400 WORDS)