Opiate inhibition of K+-induced TRH release from superfused mediobasal hypothalami in rats.

The effect of morphine and leucine enkephalin on basal and K+-induced TRH release by superfused mediobasal hypothalami in rats was investigated in an oxygenated modified Locke medium at 37 degrees C during 10 min. Both opiates (morphine, 10(-6) M; leucine enkephalin, 10(-6) M) did not modify the spontaneous release of TRH, but significantly decreased the depolarization-induced TRH release. Naloxone (10(-6) M) had no effect when added alone to the medium, but reversed the opiate inhibition of TRH release. The data suggest that endogenous opiates exert a modulatory action on TRH nerve endings in the mediobasal hypothalami, probably through presynaptic specific opiate receptors.