A morphological and autoradiographic study was made of the adrenal gland of adult male rats after autotransplantation. The simple technique involved placement of pieces of the adrenal gland in a dorsal plane between the skin and muscle. Animals for morphological studies were sacrificed at 2, 3, 4, 7, 15, 30, 90, and 180 days after autotransplantation. Those for autoradiographic studies were sacrificed at 2, 3, 7, and 15 days after autotransplantation, with 3H-thymidine being administered intraperitoneally 2 h before sacrifice. Sham-operated animals were used as controls. The majority of glandular adrenal cells suffered necrosis in the first days (2 and 3) after autotransplantation. Up until 15 days and after revascularization, morphological features of the cells were compatible with protein synthesis exhibiting a developed RER, scarce SER, and mitochondria with tubular and lamellar cristae. These data may correspond to a proliferative phase of glandular cells. At day 15, cells showed morphological signs of steroidogenic activity (mitochondria with vesicular cristae, increase of SER), and at day 30, an increased number of microvilli were seen. Between 30 and 90 days zonation of the adrenal was evident with glomerulosa, fasciculata, and reticular zones readily apparent. The quantitative analysis showed a significant increase of the volumetric density of mitochondria and microvilli between the days 7 and 30.

Autoradiographic studies showed an intense labelling of fibroblast-like cells at days 2 and 3 and of glandular cells at days 7 and 15, which was confirmed by the quantitative studies.

Corticosterone in autotransplanted animals decreased during the first 15 days, but after 30 days the values were similar to controls. The model reported here seems to be good for study of the regeneration of the adrenal gland and can be a simple, useful, and reproducible method for adrenal transplantation.