[Avoidance of renal cortical blood flow autoregulation induced by NaCl not attributable to plasma asmolarity changes...

Experiments were conducted on rats to investigate the acute effects on renal cortical blood flow and cortical autoregulation caused by intravenous administration of hypertonic solutions of sodium chloride or glucose. Local blood flow was measured in renal cortex (at 1 mm below cortical surface) by means of the hydrogen clearance method in urethanized rats. Recording of blood pressure from femoral artery was performed. In control group, renal cortical vascular resistance (R.C.V.R.)--arterial pressure relationships demonstrated typical autoregulation. An increase in plasma osmolarity of approximately 5.90%, induced by glucose, did not affect autoregulation. An increase in plasma osmolarity of approximately 4.43%, induced by NaCl, avoided autoregulation and the resistance-arterial pressure relationships became passive in appearance. In addition, NaCl administration was associated with an increase in cortical blood flow. It is suggested that in the presence of a low increment in plasma osmolarity, the sodium ion rather than the osmolarity itself, is the factor that influences cortical blood flow autoregulation in the rat.