The vasculature of the arteriole-glomerular units in variou« zones of the rat kidney
was studied by micro-angiography, and the adrenergic innervation of these units by
the histochemical fluorescence method for biogenic monoamines. In the cortical unit
the afferent arteriole, glomerular tuft and efferent arteriole are coupled in series,
whereas in the juxtamedullary unit the glomerular capillaries bud off as lateral twigs
from a continuous arteriole which leads into the medulla. These findings of an extraglomerular
medullary circulation have previously been demonstrated in man and rabbit. The cortical
and juxtamedullary units have similar innervation patterns with adrenergic nerve terminals
along both the afferent and efferent arterioles. These findings agree with evidences
presented by others of neurogenic contractions of both pre- and postglomerular vessels.
The adrenergic innervation of the continuous juxtamedullary arterioles constitutes
a morphological basis for neurogenic variations in the magnitude of the extraglomerular
circulation in the kidney with consequent changes of GFR and FF.