Plasma TSH Responses after Thyrotropin-Releasing Hormone in Young Healthy Subjects, Aged Healthy Subjects and Patients with Senile Dementia of Alzheimer Type

Abstract

In order to examine the function of the hypothalamic-pituitary-thyroid axis in the patients with senile demontia of Alzheimer type (SDAT), plasma TSH responses after thyrotropin-releasing hormone (TRH) administration were studied in 11 healthy volunteers under 48 years old (young subjects), 16 intellectually unimpaired volunteers above 60 (aged subjects) and 32 patients with SDAT. Early in the morning after an overnight fast, 500μg TRH was injected intravenously, and blood samples were obtained before administration and at 30, 60, 120 minutes after administration. TSH was measured by the double antibody radioimmunoassay. T₃, T₄ were within normal range in all subjects. The results were as follows. 1. In all the three groups, men showed significantly lower TSH responses than women. 2. With the administration of TRH, plasma TSH increased from 3.3±0.2μU/ml (mean±SE) to 12.7±2.2μU/ml in the young subjects, from 4.7±0.5μU/ml to 21.0±2.4μU/ml in the aged subjects and from 4.1±0.4μU/ml to 18.4±1.7μU/ml in the patients with SDAT. Though no significant differences in the basal TSH levels were detected between the three groups, the aged subjects and the patients showed higher TSH responses than the young subjects. 3. Out of 32 patients with SDAT, 4 patients showed blunted TSH responses (i.e. Δmax TSH<5μU/ml)and 16 patients showed delayed TSH responses (i.e. the 16 patients indicated the peak values at 60 or 120 minutes after administration). These results were discussed from the neuroendocrinological standpoints. It was supposed that the patients had multidimentional disturbance of neurotransmissions and that it influenced the neuroendocrine function of SDAT.