Animal studies have shown that dioxins influence plasma thyroid hormone concentrations. To investigate the effect of chlorinated dioxins and furans on thyroid hormone concentrations in humans, we studied 38 healthy breast-fed infants. The study population was divided into two groups according to the dioxin concentrations in milk fat of their mothers. Blood samples were taken at birth and at the ages of 1 and 11 weeks. At birth a tendency to higher total thyroxine (tT4) concentrations was found in the high exposure group. At the ages of 1 and 11 weeks the increase of mean tT4 concentrations and tT4/thyroxine-binding globulin ratios in the high exposure group reached significance as compared to the low exposure group. At birth and 1 week after birth, mean thyrotropin (TSH) concentrations were similar in both groups, but at the age of 11 weeks the mean TSH concentrations were significantly higher in the high exposure group. We postulate that the observed plasma tT4 elevation in infants exposed to dioxins before and after birth is the result of an effect on the thyroid hormone regulatory system.ImagesFigure 1.Figure 1. BFigure 2.

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In preterm infants low plasma glucose concentrations are frequently observed. We hypothesized that the infants' ability to adapt endogenous glucose production to diminishing exogenous supply is disturbed, but will improve with increasing gestational age. Glucose production rate and gluconeogenesis were measured using stable isotope techniques with [6,6-2 H 2 ]glucose and [2-13 C]glycerol in 19 preterm infants (10 Յ 30 wk and nine Ͼ30 wk gestational age) on d 5.0 Ϯ 1.4 of life. Exogenous glucose was administered at a rate of 33 mol·kg Ϫ1 ·min Ϫ1 followed by 22 mol·kg Ϫ1 ·min Ϫ1 . In the first 2 h after the decrease in exogenous supply, plasma glucose concentration declined comparably in both groups: Յ30 wk, from 4.3 Ϯ 1.2 to 3.2 Ϯ 0.9 mM; Ͼ30 wk, from 3.7 Ϯ 0.7 to 3.0 Ϯ 0.6 mM. Thereafter, only in infants Ͼ30 wk an increase was observed, to 3.4 Ϯ 0.8 mM. Glucose production rate increased comparably in both groups: Յ30 wk, from 6.0 Ϯ 4.1 to 8.8 Ϯ 3.4 mol·kg Ϫ1 ·min Ϫ1 ; Ͼ30 wk, from 7.8 Ϯ 4.6 to 11.6 Ϯ 5.2 mol·kg Ϫ1 ·min Ϫ1 . This increase was equivalent to approximately 30% of the decline in exogenous glucose. Gluconeogenesis increased comparably in both groups: Ͻ30 wk, from 3.2 Ϯ 1.2 to 4.5 Ϯ 1.3 mol·kg Ϫ1 ·min Ϫ1 ; Ͼ30 wk, from 4.3 Ϯ 1.9 to 6.8 Ϯ 2.9 mol·kg Ϫ1 ·min Ϫ1 . We conclude that preterm infants can only partly compensate a decline in exogenous glucose supply by increasing endogenous glucose production rate, probably because of limitations in the final common pathway of intracellular glucose metabolism (i.e. glucose-6-phosphatase). The ability to maintain the plasma glucose concentration after a decrease in exogenous supply is better preserved in infants Ͼ30 wk owing to more efficient adaptation of peripheral glucose utilization. Abbreviations AGA, appropriate for gestational age CI, confidence interval GPR, (endogenous) glucose production rate MIDA, mass isotopomer distribution analysis Ra, rate of appearance SGA, small for gestational age A low plasma glucose concentration is frequently found in preterm infants, particularly during the first postnatal days, and may lead to serious short-term and long-term complications. The incidence is inversely related to declining gestational age and birth weight (1-3). Therefore, preterm infants routinely receive enteral feedings or i.v. glucose shortly after birth. Despite this policy, the incidence of hypoglycemia-defined as a plasma glucose concentration Ͻ 2.6 mM-is still approximately 20% in our neonatal intensive care unit, a referral unit for infants Յ 32 wk gestational age. The high risk of hypoglycemia may be related to limited substrate stores, a high brain-to-body weight ratio, and immature enzyme systems (4 -6).The pathophysiology of low plasma glucose concentrations in otherwise healthy preterm infants is not completely understood because of lack of sufficient data on glucose kinetics. Endogenous GPR in preterm infants of various gestational ages was measured under different circumstances (6 -18). In most studies glucose was supplied at varying rates, s...

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