Chronic thyrotropin releasing hormone (TRH) administration on TRH receptors and muscarinic cholinergic receptors in CNS.

Intraperitoneal injections of thyrotropin releasing hormone (TRH, 6 mg/kg/day) to rats for 14 days resulted in a significant loss (20 25%) of TRH binding sites in the hippocampus, hypothalamus and cerebral cerebral cortex. The TRH-mediated loss was reversible and reflected a decrease in binding sites but no change in affinity. On the other hand, this TRH treatment did not affect the specific brain binding of [3H]QNB. The results suggest that TRH participates in regulating CNS-TRH receptors.