Sympathetic Innervation of Vascular Smooth Muscle in Normal and Hypertensive Animals

The nerves supplying most blood vessels are confined to an adventitial-medial plexus. This is demonstrated with both fluorescent histochemical and electron microscopic methods. A model of the vascular autonomic neuromuscular junction is proposed which explains the activation of muscle fibers on the intimal side of the media in terms of intermuscle fiber spread of activity. Species variation in sympathetic innervation of different vessels is described, including the demonstration of nerve fibers within the medial muscle coat in some large arteries and veins.

The ultrastructural features of adrenergic and cholinergic vasomotor nerves are defined. Two additional profiles which probably represent sections through a sensory nerve and a dopamine-containing cell are also described. A preliminary account of the ultrastructural pathology of sympathetic vasomotor nerves in sheep with renal hypertension is included; an increase in intra-axonal vesicles and in the size and density of their granular cores compared with control nerves is demonstrated.

The mechanism of action of some antihypertensive drugs, including guanethidine, guanacline, reserpine, and 6-hydroxydopamine, is examined with the electron microscope. Chronic treatment of rats with guanacline produces a marked deposition of lipoprotein granules in sympathetic nerves, an effect which is longlasting and perhaps irreversible.