Juxtamedullary afferent and efferent arterioles constrict to renal nerve stimulation

Sympathetic neural control of afferent and efferent arterioles of inner cortical (juxtamedullary) glomeruli has not been established, in part, because of difficulty accessing these vessels, normally located deep below the kidney surface. In this study we utilized the rat hydronephrotic kidney model to visualize the renal microcirculation and to quantitate the responses of juxtamedullary arterioles to brief (30 sec) renal nerve stimulated (RNS). Juxtamedullary afferent and efferent arterioles constricted in a frequency-dependent fashion to RNS, achieving a maximal constriction of 35% to 8 Hz stimulation. In these same kidneys, outer cortical afferent arterioles also constricted to RNS but outer cortical efferent arterioles did not. Microinjection of norepinephrine (NE) around single outer cortical efferent arterioles (to avoid the constriction of preglomerular vessels) constricted the efferent arterioles. However, the afferent arterioles of the same glomeruli were considerably more responsive to microinjected NE. Thus, the lack of constriction of outer cortical efferent arterioles to RNS may relate, in part, to their low sensitivity to NE, the primary neurotransmitter. These direct observations indicate that the juxtamedullary efferent arterioles are responsive to renal nerve stimulation whereas the outer cortical efferent vessels are not. These results, which should be cautiously extrapolated to normal filtering kidneys, indicate that glomerular hemodynamic changes evoked by the sympathetic nervous system are different for outer cortical and inner cortical glomeruli.