Characterization of humoral endorphin.

Utilizing a radioimmunoassay (RIA) with antibodies produced against leu-enkephalin, the presence of humoral endorphin in various body fluids and tissues has been shown. Pretreatment with trichloroacetic acid (TCA) was needed in all cases in order to detect the immunoreactivity. However, both treated and untreated samples of humoral endorphin were active in the opiate receptor assay. Gel filtration on Bio-Gel P-2 as well as on Sephadex G-10 columns of human cerebrospinal fluid (CSF), amniotic fluid (AF) and blood shows that they all contain a similar material with an apparent molecular weight of 1,000-1,400 daltons. Chromatography of rat brain homogenate exhibited two peaks of immunoreactivity, one of which is probably due to enkephalins and the other to humoral endorphin. The latter fraction was found to be very stable when incubated in CSF, while its degradation in blood was slightly faster. This opioid compound inhibited the electrically stimulated contractions of the guinea pig ileum; the specificity of this action was indicated by its reversal with low concentrations of naloxone. In pregnant women, humoral endorphin levels in maternal and cord blood remains stable during pregnancy, while there is a significantly higher concentration of humoral endorphin in the amniotic fluid at mid-trimester as compared to that in term pregnancies during labor.