Effect of a large dose of thyrotrophin releasing factor on pituitary and thyroid function in patients with Parkinsonism.

Thyrotrophin releasing factor (TRF) was given intravenously in doses of 0-5 mg and 20 mg to six patients with Parkinsonism treated with L-dopa. Plasma thyrotrophin (TSH), prolactin, lutenizing hormone (LH), follicle stimulating hormone (FSH), thyroxine (T4) and triiodothyronine (T3) were measured before and after TRF infusion. The observation that FSH and LH did not change in response to either dose of TRF confirmed specificity of the effects TRF for certain anterior pituitary functions. The plasma TSH and prolactin levels achieved after 20 mg TRF were considerably greater and were maintained longer than those after 0-5 mg TRF. However, despite a seven fold increase in the overall TSH response, the T4 and T3 responses to 20 mg TRF were not significantly greater than those to 0-5 mg TRF. The explanation for this discrepancy between immunoreactive TSH levels and apparent biologic effect is unclear.