Transport of triiodothyronine by erythrocytes from premature and term infants.

Abstract

To analyze hypothyroxinemia in low birth weight (LBW) infants, the initial uptake of T3 into erythrocytes from term and premature infants was measured. Thirty-eight infants and 18 prepubertal children as controls were subjected in this study. The infants were divided into group 1 (premature infants; below 2,500 g, n = 12) and group 2 (term infants; 2,501-3,500 g, n = 26). Infants with LBW for gestational age were excluded from this study. Vmax for group 1 (mean +/- SE, 6.4 +/- 0.5 pmol/min/10(8) cells), having low thyroid hormone levels, was significantly less than in group 2 (9.0 +/- 0.7 pmol/min/10(8) cells; p < 0.05). Mean Vmax for both groups exceeded normal controls (3.9 +/- 0.3 pmol/min/10(8) cells; p < 0.01). Km in the perinatal period varied widely and was essentially the same as in the normal controls. These findings indicate that T3 uptake by erythrocytes of newborns may possibly be high regardless of maturation stage and blood levels of thyroid hormones may be reflected not by change in the affinity of the transport system but by that in the number of membrane carriers.