Journal of Clinical Endocrinology & Metabolism, Vol 52, 86-90, Copyright © 1981 by Endocrine Society

ARTICLES

The effect of 3,5,3'-triiodothyronine or thyrotropin-releasing hormone on pituitary hormone responses to arginine infusions in hypothyroid patients

R LaMantia, S Spaulding and P Reese

Serum PRL and GH responses to a control arginine infusion were determined in seven hypothyroid patients. During the infusion, basal TSH levels fell slightly but significantly. On a following day, a second arginine infusion was performed, 5 min after iv injection of 500 micrograms TRH. The mean peak PRL response was enhanced 6-fold and occurred earlier, while the mean peak GH response remained unaffected. Mean peak TSH levels were only 128% above baseline after TRH. On a third day, a third arginine infusion was performed 4 h after oral administration of 100 micrograms T3; mean serum T3 levels were increased from 57 to a peak of 481 ng/dl 5 h after T3. The mean GH response was significantly reduced by 71% at 90 min, with an overall reduction of the GH output of 47%, while the PRL response remained unaffected. Thus, acute elevation of serum T3 levels in hypothyroidism appear to inhibit the mean GH response to arginine.