Radioimmunological Measurement of Beta-Endorphin in Equine Plasma

Radioimmunoassay procedures were developed and validated for the quantification of beta-endorphin (beta-EP)-like immunoreactivity in equine plasma. beta-EP could be quantitatively extracted from plasma with silicic acid powder and subsequently assayed, however, valid estimates of this hormone could also be obtained on unextracted plasma. Although beta-lipotropin (beta-LPH) cross-reacted in the assay, it was not necessary to correct for beta-LPH activity when assaying unextracted plasma because chromatographic analyses showed that 92% of the immunoreactivity in plasma extracts was similar in molecular weight to authentic beta-EP (1-31). In addition, electroacupuncture treatment did not alter the relative proportion of immunoreactivity among different molecular weight fractions.