Search

Plasma TRH was determined by radioimmunoassay in normal and abnormal thyroid state. 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). Nor were any significant differences observed in simple goitre, pituitary adenoma and empty sella. Lastly, plasma TRH and TSH levels were also evaluated after acute administration of L-dopa, 2-Br-α-ergocriptine and chlorpromazine in normal and hypothyroid subjects. Contemporaneous modifications of plasma TRH and TSH levels (decreased after L-dopa and 2-Br-α-ergocriptine, increased after chlorpromazine) were observed in hypothyroidism.The results indicate that plasma TSH modifications at birth as well as under catecholaminergic influences are at least partially mediated by variations of TRH secretion. Moreover, the inverse plasma TRH and TSH modifications in abnormal thyroid states agree with different feedback effects at the hypothalamic (positive) and pituitary (negative) level. It is possible that the significance of the positive feedback at the hypothalamic levels can be interpreted when taking into account the extra-pituitary effects of TRH.