THE EFFECT OF THYROTROPHIN RELEASING HORMONE ON THE RELEASE OF THYROTROPHIN AND OTHER PITUITARY HORMONES IN MAN UNDER BASAL CONDITIONS AND FOLLOWING ADRENERGIC BLOCKING AGENTS

Abstract

ABSTRACT Studies were performed in nine healthy male volunteers to evaluate the effect of the iv injection of 200 μg of thyrotrophin releasing hormone (TRH) on the blood concentrations of various anterior pituitary hormones, thyroxine and cortisol before and following treatment with propranolol and phentolamine, respectively. The influence on the free thyroxine index was also studied. In all subjects TRH was followed by an increase in plasma thyrotrophin (TSH) with a maximum 20–30 minutes after the injection. The increase in TSH was significantly less after treatment with phentolamine as compared to no treatment (P<0.05; paired t-test) and propranolol (P<0.02), respectively. Thus, our studies could indicate that adrenergic receptors are of importance for the TRH induced release of TSH. The plasma concentration of thyroxine and the free thyroxine index both increased significantly after TRH under all conditions studied. TRH induced no changes in the plasma levels of growth hormone, follicle stimulating hormone, luteinizing hormone and serum cortisol, indicating that TRH has a rather specific effect on the production of TSH. This specificity is not altered by either alpha- or beta-blocking agents.