Renal haemodynamics in dogs with dehydration azotaemia

Intrarenal pressure gradients and glomerular dynamics have been investigated in dogs with severe dehydration elicited by pyloric ligation. 1. Because of the proportionate decrease in arterial pressure and renal blood flow, calculated total renal vascular resistance was found unaltered as compared with normohydrated controls. The slight changes in series connected intrarenal resistances were not significant. 2. Net hydrostatic pressure across the glomerular membrane, i.e. glomerular capillary minus proximal tubular pressure was slightly diminished. The pronounced fall in effective filtration pressure was due to the considerable increase in colloid osmotic pressure of the plasma proteins. 3. Reduced arterial pressure due to clamping of the aorta did not diminish vascular resistance. Thus, the autoregulatory capacity of renal circulation seems to be lost in dehydrated animals. 4. No correlation was found between plasma NPN values on the one hand and RBF and GFR on the other. Azotaemia seemed to be due to retention and enhanced rediffusion of urea and increased katabolism of tissue proteins. 5. Reduced urine flow caused by dehydration was restored by isosmotic saline or hyperosmotic mannitol infusions. Both agents act by decreasing intrarenal vascular resistance and by diminishing the increased colloid osmotic pressure.