Ultrastructural evidence for cortico-chromaffin hybrid cells in rat adrenals?

The adrenals of perfusion fixed rats were investigated by electron microscopy. In 2 out of 12 animals studied, chromaffin cells were detected that contained organelles identical to adrenocortical mitochondria and smooth endoplasmic reticulum. The mitochondria were round-shaped with the vesicular cristae typical for steroid hormone producing cells. They were located within the cytoplasm of adrenomedullary cells neighbouring chromaffin vesicles, rough endoplasmic reticulum and the characteristic elongated mitochondria of chromaffin cells with laminar cristae. The mitochondria-like structures could be clearly differentiated from the extracellularly located synaptic endings. It can therefore be concluded that some rare cortico-chromaffin hybrid cells or chromaffin cells that present a mitochondrial-endoplasmic system of adrenocortical cells exist within the adrenal medulla. This surprising finding may offer an explanation for the long line of inconsistencies in clinico-pathological reports of adrenal morphology.