This study was designed to establish definitively the nature of immunoreactive lipotropin (IR-LPH) in human plasma and tissue extracts. Using gel filtration, gel filtration under denaturing conditions, cationic exchange chromatography, immunoprecipitation, and radioimmunoassay, we have studied normal and tumorous human pituitaries, ectopic ACTH- and LPH-secreting tumors, plasma from normal subjects before and after dexamethasone administration, and plasma from patients with primary adrenal insufficiency and pituitary and nonpituitary ACTH- and LPH-secreting tumors. Except in the plasma and tumors of occasional patients with ectopic ACTH syndrome, the smallest IR-LPH appears to be λ-lipotropin (λLPH), which is often the predominant and occasionally the only IR-LPH present. The other major peptide appears to be βLPH, a 91-amino acid molecule that contains λLPH as its 1-58 sequence. Larger immunoreactive materials were observed in some specimens, but the “big” LPH in one plasma was shown to be λLPH bound to IgG.
Koshi Tanaka, Wendell E. Nicholson, David N. Orth