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

Area of Science:

• Endocrinology
• Molecular Biology
• Biochemistry

Background:

• Corticotropin (ACTH)-like material of Mr 26,000 is known in rat extrapituitary tissues.
• The presence and characteristics of beta-melanotropin (beta-MSH) immunoactivity in these tissues are less understood.

Purpose of the Study:

• To investigate the presence and co-localization of beta-MSH immunoactivity in rat extrapituitary tissues.
• To characterize the molecular forms of ACTH and beta-MSH in these tissues and compare them to pituitary precursors.

Main Methods:

• Glacial acetic acid extraction of various normal rat extrapituitary tissues.
• Immunoassays for ACTH and beta-MSH.
• Gel filtration chromatography (Sephadex G-75) for molecular weight determination.
• Affinity chromatography using anti-ACTH immunocolumns.

Main Results:

• Beta-MSH immunoactivity was detected in all extrapituitary tissues examined, with the highest levels in the brain.
• ACTH and beta-MSH immunoactivities were strongly correlated in most tissues (excluding brain) and co-eluted as a Mr 26,000 species.
• Brain extracts showed distinct molecular forms for ACTH (Mr 4,500) and beta-MSH (Mr 8,000), with a smaller Mr 26,000 peak.
• Anti-ACTH immunocolumns adsorbed both ACTH and beta-MSH from most tissue extracts, but not from brain extracts.

Conclusions:

• ACTH and beta-MSH immunoactivities are widely distributed in rat extrapituitary tissues.
• In most extrapituitary tissues, these immunoactivities reside on the same Mr 26,000 molecule, likely related to the pituitary ACTH/beta-lipotropin precursor.
• Brain tissue exhibits unique molecular forms and processing of ACTH and beta-MSH compared to other extrapituitary tissues.