447 THE EFFECT OF POST-NATAL AGE ON THE RESPONSE OF THE PITUTITARY-THYROID AXIS TO THYROTROPIN RELEASING HORMONE

Abstract

Transient hypothyroxinemia is a common problem in the preterm infant. The response of the pituitary-thyroid (P-T) axis to exogenous thyrotropin releasing hormone (TRH) infusion has been used to confirm the euthyroid state of these preterm infants. The purpose of this study was to define the effect of post-natal age on the response of the P-T to TRH infusion. Eight preterm infants with RDS (Group I) and 10 preterm infants without RDS (Group II) received 20 mcg/kg TRH IV on days 3 and 14 of life. The mean birth weights, gestational age and Apgar scores were similar in both groups. The pattern of the serum thyroid stimulating hormone (TSH) response to TRH was similar in both groups on both days. In each group, the mean serum TSH level prior to TRH infusion was similar at day 3 and day 14. The mean serum TSH level was significantly elevated by 30 minutes (m) and declining by 180 m. At 30 and 180 m, the mean serum TSH level was significantly higher at day 3 compared to day 14. Compared to pre-infusion of TRH values, the mean serum thyroxine (T4) and triiodothyronine T3) levels were significantly increased on day 3 at 180 m in both groups. There were no other significant differences in mean serum T4 and T3 levels in either group at any other time.Conclusions: 1) In the preterm infant with or without RDS, the serum TSH response following infusion of TRH is significantly different at day 3 compared to day 14 of life; 2) the thyroid gland response is similar at 3 and 14 days.