Histological study on ouabain immunoreactivities in the mammalian hypothalamus

The endogenous digitalis-like factor (EDLF) which has recently been purified from human plasma and identified as 'ouabain', a cis-trans-cis steroid of plant origin, is thought to be similar to the hypothetical humoral factor, 'endogenous digitalis-like substance (EDLS)'. In order to examine the hypothesis that EDLS is produced in the hypothalamus, we prepared an ouabain-specific antibody, and applied it to rat and macaque brains. Ouabain immunoreactivities were observed in the hypothalamus of both species. The immunopositive neurons were distributed in paraventricular and supraoptic nuclei, and some other hypothalamic regions. Their nerve fibers were seen abundantly in the hypothalamo-neurohypophysial regions. These results strongly support the possibility of existence of cis-trans-cis steroid including EDLF in mammalian brain.