RADIOIMMUNOASSAY OF THYROTROPHIN-RELEASING HORMONE (TRH) IN NORMAL SUBJECTS, IN ABNORMAL THYROID STATES AND UNDER CATECHOLAMINERGIC INFLUENCES

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Abstract
Plasma TRH was determined by radioimmunoassay in normal and abnormal thyroid states. In euthyroid adult subjects, the plasma TRH level were 31.9 .+-. 11 pg/ml (mean .+-. SD). No significant differences were observed with regard to sex, pregnancy or age, except for the acute increase in newborn infants. The plasma TRH levels evaluated in abnormal thyroid states were found significantly (P < 0.001) increased in hyperthyroidism (49.1 .+-. 14 pg/ml) and decreased in hypothyroidism (22.1 .+-. 6 pg/ml). No significant differences were observed in simple goiter, pituitary adenoma and empty sella. Plasma TRH and TSH [thyrotropin] levels were also evaluated after acute administration of L-dopa, 2-Br-.alpha.-ergocriptine and chlorpromazine in normal and hypothyroid subjects. Contemporaneous modifications of plasma TRH and TSH levels (decreased after L-dopa and 2-Br-.alpha.-ergocriptine, increased after chlorpromazine) were observed in hypothyroidism. Plasma TSH modifications at birth and under catecholaminergic influences are at least partially mediated by variations of TRH secretion. Moreover, the inverse plasma TRH and TSH modification in abnormal thyroid states agree with different feedback effects at the hypothalamic (positive) and pituitary (negative) level. The positive feedback at the hypothalamic levels may be significant when taking into account the extrapituitary effects of TRH.