Adrenocortical response to corticotropin is potentiated by part of the amino-terminal region of pro-corticotropin/endorphin.

Abstract

Five peptides derived from pro-corticotropin/endorphin (pro-ACTH/endorphin), the pituitary corticotroph cell rohormone, were bioassayed with isolated.rat adrenocortica cells: a-and fl-melanotropin, P-lipotropin, P-endorphin, and the amino-terminal region of pro-ACTH/ endo hin known as "16k fragment." The effect of each on steroidogenesis was measured at tentially physiological concentrations (0.01-1 nM) in both the absence and presence of varying concentrations of Corticotropin (ACTH) is initially synthesized in the rat pituitary as a pro-ACTH/endorphin precursor (1-4). This glycoprotein prohormone also contains the amino acid sequences for (3-lipotropin (f3-LPH) and for a third region at the amino-terminal end of the molecule, which has been designated "16k fragment" in the literature (1,5,6). Herein, we shall use the term "16k fragment" to mean the amino-terminal region of pro-ACTH/endorphin that precedes the ACTH sequence and has an apparent molecular weight of tu16,000 by sodium dodecyl sulfate/polyacrylamide gel electrophoresis. Trypsin-like proteolytic cleavage at pairs of basic amino acid residues within the prohormone structure apparently generates these three pro-ACTH/endorphin products. In turn, ACTH and f3-LPH contain the sequences for a group of smaller peptides, including a-melanotropin (a-MSH), f3-melanotropin (f3-MSH), and ,B-endorphin. No physiological role for many of the pro-ACTH/endorphin derivatives, including 16k fragment, has been identified.Stimulated by our previous observation that a corticotroph peptide other than ACTH may account for stress-induced activation of cholesterol ester hydrolase (cholesterol esterase; sterol-ester acylhydrolase, EC 3.1.1.13) activity in the rat adrenal cortex (7), we have investigated the effect of various peptides derived from pro-ACTH/endorphin on adrenal steroidogenesis. We report here that trypsin treatment of low concentrations of 16k fragment in vitro generates a peptide(s) that is capable of substantially augmenting the stimulation of corticosterone production by ACTH-(1-24) both in isolated rat adrenocortical cells and in vivo and of increasing adrenocortical cholesterol ester hydrolase activity independently of ACTH. METHODS AND MATERIALSIsolation and Incubation of Adrenocortical Cells. Isolated rat adrenocortical cells were prepared by a modification of the method of Ramachandran and Suyama (8). Female rat adrenals were enucleated in situ and the inner zones were minced and washed with medium 199 (GIBCO). Tissue dispersion by repeated passage through a plastic pipet tip was carried out at 37°C in a mixture of medium 199, Earle's salts, 25 mM Hepes (pH 7.4), 4 mg of collagenase I per ml (Worthington), 25 ,tg of DNAse I per ml (Sigma), and an adjusted Ca2+ concentration of 2.55 mM (9). After dispersion and washing, the cells were resuspended in medium 199/Hepes containing 1 mg of lima bean trypsin inhibitor per ml (Sigma) and preincubated for 30 min at 37°C. Cells were counted with a hemacytometer and viability was determined by using trypan...

Endorphin and MSH in concert form the corticotropic principle released by tilapia (Oreochromis mossambicus; Teleostei) melanotropes

“…However, evidence is accumulating that other POMC peptides may be important for tuning corticosteroid production (18). Among these, N-terminal peptide (21,30), /3-LPH (20), various forms of MSH (9,16,34), and ^-endorphin (8) have been dem onstrated to have direct corticotropic actions, or to modulate the action of ACTH. The euryhaline teleost Oreochromis mossambicus (tilapia) read ily acclimates to environmental changes, a capacity that is accom panied by an efficient regulation of the production of cortisol, the major corticosteroid in this (3) and other teleost species.…”

Dehydroepiandrosterone Sulfate(DHEA-S) and 3',5'-Cyclic Adenosine Monophosphate(cAMP) Production in a Cultured Human Adrenocortical Carcinoma Cell Line(SW-13).

“…The concentrations of ACTH (Pedersen and Brownie 1980;Farese et al, 1983) and HCG (Meidan et al, 1985;Dyer and Erickson 1985) used in this study were much higher than those which stimulate steroidogenesis in vitro in the adrenal cortex and in the gonadal gland, respectively. Therefore, the present data indicate that SW-13 may either lack the receptors for these hormones or have some coupling defect(s) between the receptors and regulatory unit of the adenylate cyclase, if these hormones had bound to the receptors.…”

Activities of ACTH-Potentiating Substances Isolated from Rat Serum on Steroidogenes s in Isolated Rat Adrenal Cells

“…Recently, a trypsin digest of the N-terminal peptide of POMC, prepared from mouse pituitary tumor cells, and a bovine ? '3-melanotropin (MSH) synthetic peptide, representing a portion of the N-terminal peptide, have been shown to have a marked effect on the potentiation of adrenocortical response to ACTH (39,40). In another study, a naturally-occurring human pro-r-MSH glycopeptide potentiated the ACTH-induced steroidogenic response of isolated perfused rat and human adre nocortical cells (41).…”