Histologic and fine-structural anatomy of the adrenorenal portal vessels in the dog.

Reflex vasoconstriction that occurs in the kidney of the dog can be the result of activation of catecholamine flow reaching the kidney directly from the adrenal medulla via adrenorenal portal vessels. This study was undertaken to learn more about the histologic and fine-structural anatomy of these unusual vessels. We found that they are thin-walled vessels (200-500 micrometers) which are accompanied by many capillaries. These portal vessels have distinctive valves and have sparse, longitudinally arranged musculature which is denser at the base of the valves. The valves in the portal vessels are arranged to permit flow in the direction from the adrenal gland toward the kidney. Smooth muscle at the base of the valve is in close proximity to non-myelinated nerve fibers, suggesting that the opening of these valves may in part be neurally mediated. These unique anatomical features distinguish the adrenorenal portal vessels from other blood vessels and likely have functional importance in control of the adrenorenal circulation.