&lt;i&gt;In vitro &lt;/i&gt;Release of ACTH from Dispersed Rat Pars intermedia Cells. III. Multiple Forms of ACTH Biological Activity

The pars intermedia (PI) of the adenohypophysis synthesizes pro-opiomelanocortin, which, through post-translational processing, gives rise to a group of chemically related peptides, including αMSH, ACTH, CLIP, LPHs and endorphins. We investigated the control of release of these peptides using an in vitro system. We perifused either acutely dispersed rat PI cells or intact neurointermediate lobes (NI). Perifusion medium and cell extracts were subjected to a series of bioassays (BA) and radioimmunoassays (RIA) (including MSH-BA, αMSH-RIA, ACTH-BA, ACTH-RIA, LPH-RIA) and a receptor-binding assay for morphine-like activity (MLA). The relative amounts of release of the various peptide activities was examined under basal and stimulated conditions. Under basal conditions, intact NI released approximately equal amounts of αMSH immunoactivity, MSH bioactivity and MLA, slightly less ACTH and LPH immunoactivity and far less ACTH bioactivity. Relative to αMSH immunoactivity, the rate of release of ACTH bioactivity decreased in the course of an experiment while the release of the other peptide activities increased. The peptide activities were released from dispersed PI cells in relative amounts similar to those from intact NI. The relative amounts of peptide activities contained in extracts of dispersed PI cells differed from the amounts released such that when compared to αMSH immunoactivity, the release of LPH and ACTH immunoactivities and MLA is 3–4 times greater while the release of ACTH bioactivity is one-half. Serotonin (10^–7–10^–5M) markedly stimulated the release of ACTH bioactivity from both dispersed PI cells and intact NI in a dose-related manner. Serotonin had a smaller stimulatory effect on the release of αMSH and LPH immunoactivity but had no effect on the release of MLA and ACTH immunoactivity. These observations indicate that there is differential control of the release of POMC-derived peptides from the rat PI.

“…We previously reported that larger fragments of POMC also have some ACTH bioactivity [13]. We confirm the findings of Scott et al (24), that CLIP has no corticotropic activity.…”

Section: Characterisation Of the Assayssupporting

confidence: 92%

Section: Effect Of Serotonin On the Release O F Pi Peptidessupporting

confidence: 92%

Section: Fraction Numberssupporting

confidence: 73%

See 1 more Smart Citation

Differential Control of the Release of Pro-Opiomelanocortin-Derived Peptides from the Pars intermedia of the Rat Pituitary

Randle¹,

Moor²,

Kraicer³

1983

“…as suggested by the com pletely different changes noted in the concentration of bio active ACTH. Corticotropic activity of PI from adult mice and rats [8,16,37] is due to peptides of high, medium and low molecular weights; various entities containing the NH:-terminal portion of 1-39 ACTH have also been demonstrat ed in rat NIL by using R1A [8,13,17,21,24]; the relative proportion of the peptides varying according to the authors. Both high (30k) and medium (20k) molecular weight pep tides have been shown to serve as precursors in the process of biosynthesis of a-MSH and other peptides [5,18]; there is a controversy with regard to occurrence and concentration of low molecular weight ACTH [13].…”

Section: Discussionmentioning

confidence: 99%

Evidence for a Possible Dopaminergic Control of Pituitary Alpha-MSH during Ontogenesis in Mice

Schmitt¹,

Stoeckel²,

Koch³

1981

This study was aimed at determining the α-MSH and ACTH contents of the neurointermediate lobe (NIL) of the mouse hypophysis during ontogenesis, as well as the ability of the gland, incubated in a perfusion system, to respond to dopamine (DA) and high potassium (K⁺). We showed that: (1) the NIL content of α-MSH exhibited a biphasic pattern of evolution, characterized by a dramatic increase appearing between postnatal days 3 and 5. By contrast, NIL ACTH content followed a completely different pattern of evolution; (2) both DA and high K⁺ reversibly inhibited MSH release from superfused NIL, the latter effect being more pronounced with the use of pituitaries from 7-day-old than from 1-day-old mice; (3) the inhibitory influence of high K⁺ was impaired by haloperidol pretreatment. From these data, as well as from morphological observations, it appears that functional DA receptors seem to be present on melanotrophs of the developing hypophysis in mice and that the increase in α-MSH in IL cells observed shortly after birth may result from the onset of inhibitory influence exerted by dopaminergic innervation on hormonal secretion. This view, however, does not preclude possible effects of other hypothalamic releasing and/or inhibiting factors.

“…Recently, Kraicer et al [14] have shown that the ACTH biological activity re leased by stimulated 1L cells was due to 4 classes of pep tides which could be separated by gel chromatography, and only a small proportion (10%) of the total ACTH activity coeluted with ACTH1'39. Thus, we might question the chemical nature of the products which are released in our conditions.…”

Section: Discussionmentioning

confidence: 99%

<i>In vitro</i> Regulation of ACTH Release from Neurointermediate Lobe of Rat Hypophysis

Briaud¹,

Koch²,

Lutz-Bucher³

et al. 1980

Alterations in the ionic composition of the medium and different secretagogues have been used in order to study the mechanism of release of ACTH from superfused neurointermediate lobes (NIL) of rat hypophysis. We showed that: (a) a tenfold increase of K in the medium caused a reversible and repeatable stimulation of the ACTH release; (b) removal of Ca ‘ ^: reversibly abolished the stimulating effect of high K⁺: (c) removal of Ca’ had no effect on the stimulating effect of a hypothalaniic extract (HE); (d) in the latter case, a reversible significant weakening was obtained by the addition of EDTA in the Ca⁺⁺-free medium; (e) dbc-AMP caused a reversible and repeatable stimulation of the ACTH release; (f) comparable results were obtained for anterior lobes (AL) superfused in the same conditions. From these data we can conclude that Ca⁺⁺ is necessary for the stimulation of the hormonal release and that factors such as K or dbc-AMP can mimic the in vitro stimulating effect of a HE. Similarities, which appear in this study, between the modulation of the ACTH release from NIL and AL. led us to support the idea that, in vivo, a release of ACTH from the NIL, may occur in physiological conditions.