PRESSURE NATRIURESIS - ROLE OF RENAL INTERSTITIAL HYDROSTATIC-PRESSURE

The kidneys play a major role in the long-term regulation of extracellular fluid volume and arterial pressure. A central component of the feedback system for long-term control of arterial pressure is the pressure-natriuresis mechanism, whereby increases in renal perfusion pressure lead to decreases in sodium reabsorption and increases in sodium excretion. The specific intrarenal mechanism for the decrease in tubular reabsorption in response to increases in renal perfusion pressure appears to be related to increases in renal interstitial hydrostatic pressure (RIHP). Increases in renal perfusion pressure are associated with significant increases in RIHP. The mechanism whereby RIHP increases in the absence of discernible changes in whole kidney renal blood How and peritubular capillary hydrostatic and/or oncotic pressures may be related to alterations in renal medullary hemodynamics. Several lines of investigation support an important quantitative role for RIHP in mediating pressure natriuresis. Preventing RIHP from increasing in response to increases in renal perfusion pressure markedly attenuates pressure natriuresis. Furthermore, direct increases in RIHP, comparable to increases measured in response to increases in renal perfusion pressure, have been shown to significantly decrease tubular reabsorption of sodium in the proximal tubule and increase sodium excretion. The exact mechanism whereby RIHP influences tubular reabsorption is unknown but may be related to alterations in tight junctional permeability to sodium in proximal tubules and/or release of renal autacoids such as prostaglandins.