In vitro Release of ACTH from Dispersed Rat Pars intermedia Cells. III. Multiple Forms of ACTH Biological Activity

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Abstract
Both an extract of rat hypothalamus-stalk-median eminence (HE) and 5-hydroxytryptamine (5-HT) will stimulate the release of ACTH biological activity from acutely, non-enzymically dispersed rat pars intermedia (PI) cells. ACTH activity within the PI cells is composed of 4 chromatographically separable entities, but only a small proportion of the total ACTH activity co-elutes with ACTH1-39. The media, after incubation of PI cells with either HE or 5-HT was subjected to sequential chromatography on Sephadex G-50F and G-100 SF. The same 4 ACTH-like moieties as in the PI cell extracts were found. Only the release of the 2 earliest eluting components, presumably of much larger molecular dimensions than ACTH1-39, was enhanced by either HE or 5-HT. There was no augmented release of the ACTH component having molecular dimensions similar to ACTH1-39. In the in vitro system, the ACTH biological activity released from PI cells is not the size of ACTH1-39, but is composed of at least 2 much larger molecules which possess ACTH (as well as some MSH [melanotropin]) biological activity.

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