Concomitant Secretion of Adrenocorticotropin, β-Endorphin, and γ-Melanotropin from Perfused Pituitary Tumor Cells of Cushing's Disease: Effects of Lysine Vasopressin, Rat Median Eminence Extracts, Thyrotropin-Releasing Hormone, and Luteinizing Hormone-Releasing Hormone∗

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Abstract
Regulation of secretion of ACTH-, β-endorphin-, and γ-melanotropin-like immunoreactivities (ACTH-LI, β-EP-LI, and γ-MSH-LI, respectively) was studied by using a perfused Sephadex column containing dispersed pituitary tumor cells obtained from three patients with Cushing's disease. Serial dilution of the perfusion medium gave lines parallel to the standard curve in each RIA for ACTH, β-EP and γ-MSH, suggesting that immunoreactive materials in the medium are immunologically indistinguishable from the authentic peptides. Gel exclusion chromatography of the medium revealed the existence of ACTH, βlipotropin (β-LPH), β-EP, and their possible precursor protein. γ-MSH-LI consists of a major peak of big γ-MSH eluted near the elution position of β-LPH, suggesting the entire or nearly entire N-terminal portion of the precursor molecule. The addition of lysine vasopressin and rat median eminence extracts (MEE) to the perfusion system concomitantly enhanced the release of ACTH-LI, β-EP-LI, and γ-MSH-LI, although the dose-response relationship was clear-cut only in the case of MEE. TRH and LRH also elicited the concomitant release of these peptides in one patient, in whom combined administration of TRH and LRH significantly augmented plasma cortisol levels when studied preoperatively. The molar ratio of ACTH-LI to β-EP-LI was approximately 1.0, whereas γ-MSH-LI was about one fourth of ACTH-LI when compared on a weight basis. These results indicate that 1) ACTH-producing human pituitary adenomas concomitantly secrete ACTH, β-LPH, β-EP, and big γ-MSH, and 2) lysine vasopressin, MEE, TRH, and LRH act directly on pituitary cells to stimulate the release of these peptides.

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