Thyrotrophin-releasing hormone responsiveness and degradation in children with chronic renal failure: effect of time of evolution.

In order to study the hypothalamic-pituitary-thyroid function in children with chronic renal failure (CRF), the serum levels of L-thyroxine (L-T4), L-triiodothyronine (L-T3), reverse T3 (rT3), thyrotrophin (TSH) and prolactin (Prl) were measured by radioimmunoassay (RIA). Values were compared with those of normal subjects. Low levels of L-T4 were present in CRF patients as compared to controls. L-T3 was also found to be low but less than L-T4, and rT3 was lower in patients with long evolution. No alterations were observed in TSH basal levels, whereas Prl values in patients were high. After thyrotrophin-releasing hormone (TRH) administration, TSH and Prl rose to similar levels in both groups, but high values were maintained throughout (120 min) in CRF. A significant negative correlation was found between the peak rise of the TSH response and the CRF evolution time. The L-T3 response to TRH administration (120 min) was similar in both CRF and controls. The rate of in vivo and in vitro exogenous TRH degradation was decreased in patients with CRF or by their sera, respectively. Our data seem to confirm that the hypothyroid syndrome described in CRF patients is of hypothalamic origin, and the low in vivo and in vitro TRH degradation rates are a consequence of this state.