To study the effect of vatious amines on TRH contents in rat brain, various amines or inhibitor of synthesis of amines were injected into rat through i.v. or i.p.. Rats were decapitated and brain was frozen in dry ice and aceton. TRH contents in hypothalamus (H), cerebrum (C) and cerebellum and brain stem (C and S) were measured by TRH radioimmunoassay.
TRH contents in normal rats were 3.9±0.5ng in H, 2.6±0.5ng in C and 1.6±0.3ng in C and S. TRH contents in all parts of brain were increased in L-DOPA treated group and did not change in T3 or T4 treated group. TRH contents in all parts of brain were decreased in α-methyl-DOPA, α-methyl-para-tyrosine, fusaric acid and 5-HTP treated groups. In D, L-p-chlorophenylalanine treated group TRH contents in brain were increased only in hypothalamus. In L-DOPA or 5-HTP treated group with T4 or T3 preadministration, TRH contents in all parts of brain were same levels of L-DOPA or 5-HTP treated group.
The above data suggested the TRH contents in rat brain were increased with increase of dopamine level in rat brain and decreased with increase of serotonine level or decrease of noradrenaline level in rat brain and inhibitory effect of T4 or T3 on TRH release might be mediated through dopaminergic and serotonergic mechanism.