Effect of Synthetic Thyrotrophin Releasing Hormone (TRH) in Man

Summary: Synthetic TRH (200 μ g) administered intravenously to twelve normal subjects produced a consistent rise in serum thyrotrophin (TSH) levels reaching a peak 20 – 30 mins following the injection. No reproducible effects were seen on plasma levels of GH, LH, FSH or 11 -hydroxycorticoids measured concomitantly with TSH. Mean free thyroxine index following TRH rose by 23% at 60 and 120 mins. Two subjects treated with triiodothyronine and 17 untreated thyrotoxic patients showed marked impairment of TSH response to TRH. Reduced or absent TSH responses were likewise observed in five euthyroid patients with Graves' disease, two with ophthalmopathy as the sole manifestation of the disease. In ten patients with primary hypothyroidism, synthetic TRH evoked further increases of elevated basal TSH levels with exaggerated over-all responses. Five of seven euthyroid patients with pituitary tumours showed blunted TSH responses whereas all six patients with secondary hypothyroidism (resulting from pituitary or suspected hypothalamic lesions) exhibited normal or slightly exaggerated responses.
It is concluded that synthetic TRH is a specific stimulus to pituitary TSH release with considerable potential in the diagnosis of mind disturbances of thyroid function. Its use should promote better understanding of hydothalamic-pituitary-thyroid relationships.