Identification of 3,3'-T2S as a fetal thyroid hormone derivative in maternal urine in sheep
Wu, S.Y.; Polk, D.; Fisher, D.A.; Huang, W.S.; Reviczky, A.L.; Chen, W.L.
American Journal of Physiology 268(1 Pt 1): E33-E39
1995
ISSN/ISBN: 0002-9513 PMID: 7840179 Document Number: 440436
We measured 3,3'-diiodothyronine sulfate (T-2S) in serum and urine (n = 5-6) obtained from euthyroid fetal (94-145 days of gestation, term = 150 days), newborn, and adult sheep and in serum and urine samples from ovine fetuses 13 days after total thyroidectomy conducted between 110 and 113 gestation days (n = 5). Sham-operated twin fetuses served as controls (n = 5). Mean serum T-2S concentrations increased progressively from 94 days (74 ng/dl) to 130 days (420 ng/dl), decreasing thereafter to 145 days (197 ng/dl). T-2S concentrations in fetal urine peaked at 110 days (117 ng/dl). In hypothyroid fetuses, mean serum and urine T-2S were 60 and 53% of control values. T-o assess the possibility that the T-2S in maternal serum/urine is derived from fetal serum 3,5,3'-triiodothyronine (T-3), we measured T-3, T-3 sulfate (T-3S), and T-2S in fetal serum and in maternal serum and urine after bolus infusion of T-3 to the fetus (n = 4). Additionally, T-3, T-3S, and T-2S concentrations were measured in maternal serum and urine after T-3 infusion to the maternal ewes (n = 4). Fetal T-3 infusion rapidly increased fetal serum T-3S and T-2S. Maternal serum and urine T-3S and T-2S concentrations increased, whereas T-3 concentrations remained unchanged. Maternal T-3 infusion increased in serum and urine T-3S and T-2S levels, but the levels, relative to T-3, were less than values measured after fetal T-3 infusion. We conclude that T-2S is a normal thyroid hormone metabolite in the ovine fetus and suggest that a major pathway of fetal T-2S production is T-3 to T-3S to T-2S. Both T-3S and T-2S appear to readily traverse the placenta to appear in maternal serum and urine.