RENAL-FUNCTION RESERVE AND SODIUM SENSITIVITY IN ESSENTIAL-HYPERTENSION

It has been postulated that glomerular capillary pressure is elevated in sodium-sensitive types of hypertension, In addition, the presence o r absence of renal function reserve, in response to a chronic protein load, is thought to be useful in predicting the existence of glomerula r hypertension. Intrarenal hemodynamic parameters in the sodium-sensit ive type of essential hypertension were therefore calculated by analyz ing the pressure-natriuresis curve, and the preservation of renal func tion reserve was evaluated. Fifteen patients with essential hypertensi on were maintained on a normal sodium diet for 1 week and a low-sodium diet for a second week in study 1. This protocol was repeated for low and high protein intake in 8 patients in study 2. Subjects in study 1 whose mean arterial pressure was reduced by more than 10% by sodium r estriction were considered sodium sensitive (n = 7), with the remainin g patients classified as non-sodium sensitive (n = 8). There were no s ignificant differences in mean arterial pressure (125 +/- 2 mm Hg), gl omerular filtration rate (80 +/- 3 ml/min), or renal plasma flow rate (355 +/- 24 ml/min) on the normal sodium diet between sodium-sensitive and non-sodium-sensitive patients. Glomerular capillary pressure (59 +/- 2 mm Hg vs 47 +/- 1 mm Hg, p < 0.0002) was estimated to be elevate d in sodium-sensitive patients relative to that in non-sodium-sensitiv e patients, whereas the whole kidney ultrafiltration coefficient of gl omerular capillary walls (0.068 +/- 0.009 (ml/sec)/mm Hg vs 0.221 +/- 0.042 (ml/sec)/mm Hg, P < 0.005) was decreased, Chronic protein loadin g increased both glomerular filtration and renal plasma flow rates in study 2, Although the sodium sensitivity of blood pressure showed no s ignificant correlation with the increase in either glomerular filtrati on or renal plasma flow rate, it showed a weak negative correlation wi th the increase in filtration fraction (r = -0.69, p < 0.06), which is the ratio of the two rates. Taken together, these results suggest tha t glomerular capillary pressure is elevated and renal function reserve is impaired in patients with sodium-sensitive essential hypertension.