Structural Evidence in Support of an Urinary Tract Pacemaker

SUMMARY Using light and electron microscopic techniques, the arrangement and distribution of smooth muscle and of noradrenergic nerves has been examined in the multicalyceal upper urinary tracts of the pig and human. Smooth muscle confined to the renal attachment of each minor calyx appeared structurally different from that which extended throughout the major calyces, renal pelvis and upper ureter. The two types of muscle, however, were in continuity with one another. A relatively rich supply of noradrenergic nerves was also identified in relation to these modified smooth muscle cells adjacent to the renal parenchyma; very few similar nerves were seen amongst the muscle bundles in the remainder of the upper urinary tract. In conjunction with other studies, it is proposed that these observations are best interpreted as structural evidence for a pacemaker system localised to the proximal part of the urinary tract in these species.