The effects of metopirone (SU-4885) and aldactone (SC-9420) on the histology and histochemistry of the interrenal tissue of male common frogs, Rana temporaria, have been studied. From the changes in nuclear and cellular size, mitotic rate, and lipid and cholesterol content it has been concluded that in intact animals the administration of metopirone as well as of aldactone resulted in an increase of the interrenal secretory activity. The effects were very similar to that of ACTH. Ablation of the pars distalis prevented the interrenal activation by metopirone. The effect of aldactone was markedly reduced in operated frogs, but some stimulation remained. It is suggested that both substances act by way of enhancing pituitary ACTH ouput. The dependence of the secretion of corticosteroids on pituitary ACTH is discussed.
I wish to thank Dr. W. J. van Dongen for his cooperation and criticism and for enabling me to do this work in his laboratory. I am endebted to Prof. Dr. P. G. W. J. van Oordt for his valuable and constructive suggestions. Thanks are also due to Miss Mieke Roelofsen and Miss Ineke Wienen for their conscientious technical assistance.