Distribution of TRH-potentiating peptide (Ps4) and its receptors in rat brain and peripheral tissues.

TRH-potentiating peptide (Ps4) is a peptide originally isolated from bovine hypothalamus, which corresponds to the deduced rat prepro-TRH-(160-169) sequence. We have examined the distribution of Ps4 and [125I-Tyr0]Ps4 binding sites in various rat tissues. Very high specific binding of [125I-Tyr0]Ps4 was observed in pituitary membranes. Almost identical relative magnitude of binding was found in spinal cord, hypothalamus, hippocampus and olfactory lobe. In addition, a high density of Ps4 binding sites was demonstrated in urogenital organs. The observed distribution pattern of Ps4 in brain tissues was similar to that reported for TRH, with high concentrations in the hypothalamus and significant amount in spinal cord and olfactory lobe. These findings support the hypothesis that the TRH-potentiating peptide could act as neuromodulator or neurotransmitter in the central nervous system (CNS). In peripheral tissues, very low concentrations of Ps4 were detected except in testis which seems to be the major locus for Ps4 biosynthesis. This study demonstrated for the first time that TRH-potentiating peptide and its receptors are widely distributed in the CNS and peripheral tissues.