A microscopic and stereological study of the renal artery transitional zone of the adult male dog

A transitional zone in the dog renal artery was documented and its parameters were recorded: length and volumes of the luminal wall, tunica intima, tunica media, and tunica adventitia-as well as these parameters in the non-transitional zone of artery. Twelve normal adult male dogs were studied. The specimens were processed in the routine manner for light and electron microscopy. After the determination of transitional zone length by light microscope, for the stereological study each renal artery was divided into transitional and non-transitional zones, and paraffin blocks were prepared. It was established that the transitional zone contains parallel and continuous elastic fibers. In this zone the elastic fibers in the extracellular space were greater in number than collagen fibers. However, in the non-transitional zone the rows of smooth muscle cells increased in number, there were more collagen fibers than elastic fibers in the extracellular space, and the elastic fibers appeared to be fragmented. The transitional zone showed an intermediate structure-between elastic and muscular arteries-and was 15 mm in length in the right and left renal arteries. There were more dense bodies in the non-transitional zone than in the transitional zone. The volumes of the lumen, tunica intima, tunica media, and tunica adventitia in the transitional zone were greater than in the non-transitional zone on both sides; in the right renal artery they were larger than in the left one in the 2 zones.