The Adrenal Medulla as a Target Organ in Toxicologic Studies of Rats and Mice
Among the endocrine organs, the adrenal gland is reportedly the most susceptible to compound-induced lesions (Ribelin, 1984). The cells of the adrenal medulla are derived from neural crest ectoderm in contrast to the mesodermal origin of the adrenal cortex. The different origins and functions of the two components of the adrenal make them susceptible to different toxicologic insults and evoke different types of responses. In the medulla, proliferative lesions are the most common pathological finding. There can also be degenerative changes, although these are less common. The proliferative lesions include diffuse or nodular hyperplasia; benign, malignant, or complex pheochromocytoma; ganglioneuroma; and neuroblastoma. Proliferative lesions can be spontaneous or can be induced by chemicals
and dietary modifications. In general, both spontaneous and xenobiotic-induced medullary proliferative lesions tend to be much more frequent in rats than in mice and, in rats, most studies report a higher incidence in males than in females (Tischler et al., 1997; Tischler, 1994).