[TRH receptor-related signal transduction mechanism]

TRH receptor-related signal transduction mechanism in the pituitary cells and the central nervous system was reviewed. In pituitary cells, TRH binds to its specific receptor on the cell membrane, followed by hydrolysis of inositol phospholipids by activation of phospholipase C leading to an increase in inositol 1,4,5-trisphosphates (IP3) and diacylglycerol (DG). IP3 mobilizes intracellular Ca2+, which activates Ca2+ and Calmodulin dependent protein kinase (Ca-CaM kinase) and DG activates protein kinase C (PKC). Both Ca-CaM kinase and PKC phosphorylates several proteins in the nucleus, plasma membranes, and cytosol resulting in cell responses including hormone secretion and gene expression. Protein dephosphorylation is also involved in TRH action in the pituitary. In the central nervous system, TRH possesses different intracellular signaling systems, which vary with brain regions.