Radioimmunoassay of pro-gamma-melanotropin, the amino-terminal fragment of proopiolipomelanocortin.

A RIA has been developed for natural porcine pro-gamma MSH, the 103-amino acid peptide that represents the amino-terminal part of proopiolipomelanocortin. Rabbits were immunized with the purified peptide polymerized with glutaraldehyde. The antiserum is directed against the amino-terminal end of the antigen and does not cross-react with corticotropin, beta-lipotropin, beta-endorphin, gamma 3MSH, or gamma 2MSH. The minimum detectable concentration is 0.15 ng/ml standard pro-gamma MSH (15 pg/tube). Pro-gamma MSH-like immunoreactivity was detected in plasma and extracts of the hypothalamus and pituitary of pigs. Gel chromatography of these extracts revealed at least three immunoreactive peaks in the anterior and neurointermediate lobes of the pituitary, whereas two immunoreactive peaks were found in extracts of the hypothalamus.