Unidirectional interaction between thyrotropin releasing hormone and opiates at the level of their brain receptors.

The effect of TRH and its analogs, MK771 and RX-77368 on the binding of [3H]D-serine-6-threonine-leucine enkephalin (delta opiate receptors), [3H]ethylketocyclazocine (kappa receptors) and [3H]naltrexone (mu receptors) to the rat brain membranes was determined. Neither TRH nor its analogs affected the binding of ligands for mu, delta, and kappa opiate receptors at either 35 or 0 degrees C. Since previous studies from this laboratory indicate that the drugs acting at the kappa, and delta opiate receptors inhibit the binding of [3H](3-MeHis2) TRH to brain TRH receptors, the present studies suggest a unidirectional interaction between opiates and TRH in the brain at the level of their receptors.