Corticotropin/lipotropin common precursor-like material in normal rat extrapituitary tissues.

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Abstract
A MW 26,000 ACTH-like material is present in glacial acetic acid extracts of all normal rat extrapituitary tissues. In the present study, .beta.-melanotropin (.beta.-MSH) immunoactivity was detected in glacial acetic acid extracts of normal rat extrapituitary tissues. .beta.-MSH immunoactivity was also present in all extracts (mean .+-. SEM, f[femto]mol/mg of protein): brain, 71.0 .+-. 16.3; stomach, 11.5 .+-. 1.6; kidney, 8.9 .+-. 0.8; colon, 8.2 .+-. 1.1; small intestine, 6.5 .+-. 1.1; liver, 4.3 .+-. 0.5; and heart, 3.2 .+-. 0.5. Except in brain extracts, .beta.-MSH and ACTH immunoactivities of tissue extracts were strongly correlated to each other (r = 0.79; n = 42). When tissue extracts (except brain) were passed through a Sephadex G-75 (superfine) column, ACTH and .beta.-MSH immunoactivities were eluted in a single peak corresponding to MW 26,000. In contrast, for brain extracts, the MW of major peaks of ACTH and .beta.-MSH immunoactivities were 4500 and 8000, respectively; a smaller peak of MW 26,000 ACTH/.beta.-MSH-like material was also eluted. Specific anti-ACTH immunocolumns, which did not bind purified synthetic .beta.-MSH, adsorbed both ACTH and .beta.-MSH immunoactivities of all tissue extracts except those of brain. One-third of the .beta.-MSH immunoactivity in brain extracts adsorbed to the anti-ACTH immunocolumn, but 2/3 of .beta.-MSH immunoactivity passed through the column. ACTH and .beta.-MSH immunoactivities are present in all normal rat extrapituitary tissues and exist in most tissues on the same molecule. This MW 26,000 molecule is closely related to the pituitary ACTH/.beta.-lipotropin common precursor.