Big form of gamma-melanotropin-like immunoreactivity in normal human plasma

Using a radioimmunoassay for gamma 3-melanotropin (gamma 3-MSH), gamma-melanotropin-like immunoreactivity (gamma-MSH-LI) was detected in plasma extracts of normal subjects before and after metyrapone administration. Plasma gamma-MSH-LI from four normal men rose significantly after a single oral administration of metyrapone (30 mg/kg of body weight). Gel chromatographic study of plasma extract after metyrapone administration showed a single peak of gamma-MSH-LI near the elution position of mouse 16K fragment, however smaller forms of gamma-MSH-LI were not detected.