Morphological changes of the toad adrenal tissue grafted in the median eminence-pars distalis region

Abstract

The present investigation was designed to determine the morphological changes under-gone by the adrenal gland when grafted into the hypophysial region, paying special attention to the possibility that it might differentiate into pars distalis-like cells. The pars distalis of the hypophysis of 33 male and female toads was carefully dissected out, leaving the vascular supply, and the neural afferents, to the median eminence and neurointermediate lobe intact. Then a fragment of adrenal tissue from a donor toad was implanted in the region that had been occupied by the pars distalis. The operated animals were killed 1, 2, 3, 4, 5, 10 and 12 weeks after the operation. Within each group one animal was used for light microscopic studies and the others for electron microscopy. The graft samples obtained from the 5 week group animals were fixed in glutaraldehyde and then incubated with either amoniacal silver or with zinc iodide-osmium tetroxide mixture at pH 4.4. These two methods stain selectively the noradrenaline storing granules. The grafted adrenal tissue became revascularized by the portal vessels. Histochemical studies did not reveal the presence of pars distalis-like cells in the graft, even 3 months after the operation. Within the first 2 weeks after the operation, a population of cortical cells underwent involution, whereas a second type of cortical cells remained unchanged. During this phase two types of chromaffin cells, similar to those observed in the gland in situ, were distinguished. During the chronic experimental phase all cortical cells showed involution and only one type of chromaffin cell was identified. The latter were loaded with chromaffin granules and displayed numerous processes contacting the perivascular space. The histochemical characteristics of these cells indicate that they are noradrenaline secreting cells. It is concluded that under the present experimental conditions, the grafted adrenal tissue does not differentiate into pars distalis and that only one cell type of the transplanted tissue continues to secrete its specific cell product.