[Studies on Hypothalamic-Pituitary Thyroid regulation in Hemodialysis Patients (author's transl)]

During hemodialysis a continuous determination of free thyroid hormone and the basic TSH value was performed in 43 patients. a significant increase of free thyroxine and triodthyronine was found as well as a significant decrease of the TSH basal concentration in serum, which was already subnormal before hemodialysis. In 14 patients a TSH-TRH-test was performed before, during and after hemodialysis. A considerable reduction of the pituitary sensitivity to TRH administration during dialysis was found as compared with values before and after hemodialysis. Because of the increase of free hormone concentration, the reduction of TSH serum concentration and the decrease of pituitary sensitivity to TRH are considered to be a physiological reaction of the pituitary. On the other side a significant increase of the binding affinity of the T3 and T4 nuclear cell receptors correlated with concentration of heparin could be demonstrated. Because this modulation would induce an increasing occupation of the binding valences with thyroid hormone molecules, with a resulting decrease of the production of TSH, this process could also explain the results. Because ther is only a linear relation between the number of occupied nuclear binding sets and the TSH metabolism for T3, the physiological reaction of the pituitary is dependent on an intact conversion of T4 to T3 intracellular. A possible partly defect of this monodeiodination at hemodialysis patients could also explain the published different results concerning the basic concentration of TSH in the serum and the TSH-THR-test.