Abstract Introduction: Although numerous neurons expressing tyrosine hydroxylase (TH), the first enzyme of catecholamine synthesis, were discovered in the supraoptic nucleus (SON) of hypothalamus in animals almost forty years ago, mainly under osmotic stress, the functional significance of TH there remains unclear. Therefore, the aim of this study was to test our hypothesis that TH in these neurons has enzymatic activity capable of converting L-tyrosine to L-3,4-dihydroxyphenylalanine (L-DOPA).
