Corticotrophin-Like Peptides in the Rat Pituitary

Abstract

SUMMARY The pars intermedia of the rat pituitary contains a peptide resembling the 18–39 portion of adrenocorticotrophic hormone (ACTH), which has been termed 'corticotrophin-like intermediate lobe peptide' (CLIP). It can be detected by its cross-reaction with an antiserum directed against the CO2H-terminal portion of the ACTH molecule; it has an amino acid composition identical to the 18–39 portion of human ACTH, except for one less glycine and an extra valine residue, and it is rapidly released from neurointermediate lobes maintained in organ culture. The pars intermedia also contains a peptide with an amino acid composition and biological potency identical to that of melanocyte-stimulating hormone (α-MSH) isolated from other mammals, and which accounts for the bulk of melanocyte-stimulating activity in the pituitary. Rat ACTH resembles human ACTH in amino acid composition, except for an extra valine and one less glycine residue. On the basis of these data it is proposed that ACTH is the precursor of α-MSH and CLIP, which are both present in the cells of the pars intermedia.

Presence of corticotropin in brain of normal and hypophysectomized rats.

“…Immunoreactive (midportion antibody) and bioreactive ACTH concentrations of median eminence and medial basal hypothalamus observed in the present study are approximately 1/25th and 1/30th respectively, of those observed by us and others (22) for whole pituitary. Posterior pituitary concentrations of bioreactive ACTH have been reported (22)(23) to be one-fourth of those found in the anterior lobe; most of the ACTH content of the posterior pituitary (which includes both pars intermedia and posterior lobe) is material with COOHterminal-like immunoactivity (COOH-terminal/bioreactive ratio, approximately 100:1) (22). Since the weight of median eminence plus medial basal hypothalamus is about one-third that of the pituitary, the total amount of bioreactive ACTH in this area is roughly 1/100th that in pituitary.…”

“…The elution pattern from Sephadex G-50 gel filtration was arbitrarily divided into three sections (to represent activity of the three peaks present: fractions 8-11, 12-16, and [17][18][19][20][21][22] and the percentage of the total immunoreactivity (midportion antibody, this being more representative of biological ACTH § The NH2-terminal antibody reacts almost equally on a molar basis with ACTHI-39, ACTH'24, and a-MSH but not with ACTH17-9, ACTHII-24, or ACTHI-10; the midportion antibody reacts with ACTH1-39 and ACTHII-24 on an equimolar basis, but not with a-MSH, j3-MSH, ACTHI-10, or ACTH17-9. …”

<i>In vitro</i> Release of ACTH from Dispersed Rat Pars Intermedia Cells. II. Effect of Neurotransmitter Substances

“…The immunohistological results, however, are not definitive because of the commonality in amino acid sequences between ACTH and «MSH [Li, 1972;Baker, 1973;Howe, 1973], and between ACTH and the corticotropin-like intermediate lobe peptide [Scott et al, 1974] and lipotropin [Li, 1972]; the latter 2 peptides are also present in the PI [Moon et al, 1973;Dessy et Herlant, 1974;Scott et al, 1974].…”

<i>In vitro </i>Release of ACTH from Dispersed Rat Pars Intermedia Cells. I. Effect of Secretagogues

“…Thus the same cell appears to contain a number of peptides including *MSH, ACTH activity, and a corticotrophin-like intermediate lobe peptide (CLIP) [Scott et al, 1974] and perhaps also lipotrophins [Dessy and Herlant. 1974], all with common amino acid sequences.…”