Serum thyroxin levels during hyperthermia evoked in the monkey by intrahypothalamic injection of PGE1, 5-HT or pyrogen.

Serotonin (5-HT), prostaglandin E1 (PGE1) or a bacterial pyrogen (E. coli or S. typhosa) was microinjected in a volume of 1.0--1.5 microliter into the hypothalamus of the unanesthetized monkey to evoke a long-term hyperthermia. Samples of venous blood collected every 15 min, before, during and after each fever were analyzed by radioimmunoassay for plasma thyroxin levels. There was no statistically significant correlation between plasma thyroxin values and a given phase of the hyperthermic episode induced by the microinjections of 5--HT, PGE1 or bacteria. The possibility that an enhanced release of the thyroid hormone serves to sustain a long-term elevation in temperature evoked by a centrally acting pyrogenic substance is not supported.