Radioimmunoassay for 3',5'-diiodothyronine. [/sup 125/I tracer technique]

Journal Article · Wed Nov 01 04:00:00 EST 1978 · J. Clin. Endocrinol. Metab.; (United States)

DOI:https://doi.org/10.1210/jcem-47-5-1059· OSTI ID:6542675

Burman, K D; Wright, F D; Smallridge, R C; Green, B J; Georges, L P; Wartofsky, L

The present report describes a RIA for 3',5'-diiodothyronine (T/sub 2/) that can be performed on unextracted serum and which has a lower limit of detectability of 2 ng/dl. Cross-reactivity with other iodothyronines was negligible, except for rT/sub 3/ which began to demonstrate cross-reactivity when rT/sub 3/ levels were elevated to 180 ng/dl. Employing this RIA for T/sub 2/, we have determined that 83 healthy individuals had a mean (+-SE) serum T/sub 2/ concentration of 5.0 +- 0.3 ng/dl, thyrotoxic subjects (n = 12) had a mean T/sub 2/ level that was elevated to 10.8 +- 0.8 ng/dl, and each of 6 hypothyroid subjects had undetectable (<2 ng/dl) concentrations. Athyreotic patients (n = 8), receiving 0.4 mg T/sub 4/ daily, had serum T/sub 2/ concentrations of 15.0 +- 3.0 ng/dl. Fasting in obese subjects was associated with an increase in serum T/sub 2/ to 6.9 +- 0.6 ng/dl from a basal level of 4.4 +- 0.4 ng/dl in the fed state (P < 0.01). Despite the fact that rT/sub 3/ levels may be elevated in amniotic fluid and that rT/sub 3/ is expected to represent the major source from which extrathyroidal T/sub 2/ arises, T/sub 2/ levels were low in amniotic fluid, being undetectable (<2 ng/dl) in 9 of 19 samples; the mean (+-SE) T/sub 2/ concentration in the 10 detectable samples was 5.4 +- 1 ng/dl. These data indicate T/sub 2/ is a normal component of serum and that the majority of serum T/sub 2/ is probably derived from peripheral conversion. Furthermore, these observations suggest that situations associated with elevated rT/sub 3/ levels (e.g., thyrotoxicosis and fasting) may also have increased T/sub 2/ values.

• Research Organization: Walter Reed Army Medical Center, Washington, DC
• OSTI ID: 6542675
• Journal Information: J. Clin. Endocrinol. Metab.; (United States), Journal Name: J. Clin. Endocrinol. Metab.; (United States) Vol. 47:5; ISSN JCEMA
• Country of Publication: United States
• Language: English

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