Oscillations in reverse triiodothyronine levels in serum of healthy infants aged 0 to 130 hours.
rT3 was measured by RIA in sera from 273 normal healthy infants between 0--130 h of age. The curve for the mean rT3 level plotted against age was polyexponential in shape and showed superimposed oscillations with a period of about 16 h, similar to the curves for T4, T3, and TSH previously found for the same group of subjects (J Clin Endocrinol Metab 47: 61, 1978). The ratio of concentrations of rT3 to T4 remained approximately constant, with a mean value of 0.016 over the age range of 3--130 h. These observations suggest that the variations in rT3 levels in newborn serum during the first few days of life are largely accountable by variations in T4 substrate concentrations.
D006801:Humans; D007231:Infant, Newborn; D010507:Periodicity; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood*; D014285:Triiodothyronine, Reverse / Q000097:blood*
D014284:Triiodothyronine; D014285:Triiodothyronine, Reverse; D013974:Thyroxine