Effects of synthetic thyrotropin-releasing hormone on plasma thyrotropin, growth hormone and insulin levels in man.

Abstract

The responses of TSH, GH and insulin secretion to synthetic TRH were investigated in 6 normal subjects and 13 patients with endocrinopathies. Intramuscula injection of TRH in dose of 500 μg stimulated TSH secretion in normal individuals with the peak values of 8.0 to 20.0μU/ml at 20 or 40min after the injection. Three out of 4 patients with hyperthyroidism showed no response, the serum TSH level remaining undetectable up to 180min and one showed a minimal response at 40min. A patient who had been given orally a dose of 30mg per day of methimazole for 2weeks showed an exaggerated response, and a patient with chronic thyroiditis, who had a slightly elevated plasma TSH level at zero time, also showed a supernormal response as in cases of two acromegalics. No rise in plasma TSH occurred in a patient with hypopituitarism. All euthyroid patients with other endocrinopathies responded to synthetic TRH as in normal subjects. Plasma GH levels did not show any significant change up to 90 min, but later increased slightly during 120-180 min in the majority of cases. It may indicate that this increment is not a primary but a secondary effect of TRH or due to some stress-like factors. In acromegalic patients, a considerable rise in plasma GH level was observed to begin at 20min in response to TRH. In all cases, plasma insulin secretion did not change throughout the study.It can be concluded that synthetic TRH is a useful tool for testing the pituitary reserve of TSH and for elucidating the pathophysiology of hypothalamo-pituitarythyroid axis.