Effects of pneumadin (PNM) on the adrenal glands. 6. Further studies on the inhibitory effect of PNM on dexamethasone-induced

Abstract

Pneumadin (PNM) is a biologically active decapeptide, which has previously been found to enhance rat adrenal growth; the mechanism is indirect and probably involves the stimulation of both argininevasopressin (AVP) and ACTH release. The effects of 2- and 6-day PNM administration on the atrophic adrenal cortices of rats treated for 8 and 12 days, respectively, with daily subcutaneous injections of 15 or 40 g1100 g body weight of dexamethasone (Dx) were investigated. Morphometry showed that PNM counteracted Dxinduced adrenal atrophy, by preventing the decrease in volume and number of the parenchymal cells. PNM raised aldosterone and corticosterone production of adrenal quarters from Dx-treated rats, but it did not evoke significant changes in the plasma concentrations of the two hormones. The preventive effect of PNM was only partial and almost exclusively evident in rats administered the lower dose of Dx. In light of these findings the following conclusions are drawn: (i) PNM is able to partially overcome the Dx-induced inhibition of the rat hypothalamo-pituitary-adrenal axis, probably by stimulating the pituitary release of AVP and ACTH, that in turn enhance adrenocortical growth; (ii) the PNMinduced improvement of the secretory capacity of atrophic adrenocortical cells is not sufficient to raise the blood leve1 of corticosteroid hormones; and (iii) Dx exerts a direct inhibitory action on adrenocortical cells, which is not counteracted by PNM.