BETA-ENDORPHIN IMMUNOREACTIVITY IN RAT AND HUMAN-BLOOD - RADIOIMMUNOASSAY, COMPARATIVE LEVELS AND PHYSIOLOGICAL ALTERATIONS

Antiserum against human β-Endorphin (βhEP) has been obtained from rabbit. The antiserum, diluted 1 1500 bound I125 βh-EP, demonstrating an effective range from 10pM to 10nM. The sensitivity of the assay is 2-3 fmoles. This antibody exhibits 10-15% cross-reactivity with human β-Lipotropin (βh-LPH). β-EP-like immunoreactivity in rat blood has been detected in unextracted samples when compared to blood from hypophysectomized rats. The whole assay and calibration curves are carried out in plasma from hypophysectomized animals. β-EP-like immunoreactivity can be detected in normal rat plasma (75 ± 15 fmole/ml), and exhibits substantial increases with adrenalectomy (287 ± 32 fmoles/ml). In contrast, samples from five healthy normal human males gave values near the limits of detection of the assay (12 fmoles ± 3.9 per ml of plasma). Such values may be due to cross-reactivity of the antiserum with βh-LPH or other circulating hormones. In contrast, patients with elevated ACTH production and normal pregnant humans exhibit significantly elevated levels of β-EP immunoreactivity in plasma. © 1979.