ON THE PRESENCE OF PRECORTICOTROPHIN – A PRECURSOR OF CORTICOTROPHIN IN VARIOUS MAMMALIAN HYPOPHYSES

Abstract

Pituitary extracts of various species origin such as beef, sheep, pig, guinea-pig, rabbit and rat prepared in 0.9 per cent sodium chloride solution were assayed for corticotrophic activity, before and after acid treatment of the samples, by the adrenal ascorbic acid depletion method. The corticotrophic activity per mg of the pituitary tissue of sheep, pig and guinea-pig is comparable, but is considerably less than that of rat and rabbit pituitary glands. At the dose level of 0.25 mg wet weight of pituitary tissue per 100 g of body weight of the assay animals, the pituitary glands of all species except rabbit did not show any corticotrophic activity before acid treatment. However, after acid activation of the preparations significantly higher corticotrophic activity was detectable at this dose level. It is concluded that the presence of precorticotrophin in the mammalian adenohypophysis is a general phenomenon; at least 80 per cent of the total corticotrophic activity of the pituitary glands exists in the form of precorticotrophin; pig pituitary gland would be a suitable starting material for the separation of precorticotrophin from other pituitary factors. Cold stress caused substantial depletion in the pituitary glands of both corticotrophin and precorticotrophin. Corticosterone treatment and adrenalectomy caused a profound decrease in the corticotrophin content of the hypophysis but precorticotrophin was clearly demonstrable.