Presence of ACTH-Potentiating Factors in Rat Anterior Pituitary Glands

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Abstract
High MW ACTH fractions, obtained through gel filtration of boiled rat anterior pituitary extract, induced a marked increase in corticosterone production from isolated rat adrenal cells in the presence of low concentrations of ACTH-(1-24). This indicates the presence of heat-stable factors augmenting the steroidogenic action of ACTH in the rat anterior pituitary. These factors potentiated the activity not only of ACTH-(1-24) but also of ACTH-(1-18). The ACTH-potentiating factors in rat anterior pituitary extract are possibly present in heterogeneous forms, according to their MW (8000,10,000 and 15,000), their mobility in ion-exchange chromatography and their content in radioimmunoassay-ACTH activity. Of these 3 forms, the former comigrated with biological ACTH activity. The remaining 2 forms were free of it. Since the effect of potentiating factors on modified ACTH-(1-19), shown to be less susceptible to proteolytic degradation than ACTH-(1-24), was similar to the effect on ACTH-(1-24), potentiation apparently was not due to an inhibition of ACTH proteolysis.

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