Figure 237

Plasma renin activity (PRA) and atrial natriuretic peptide (ANP) concentration in the nephrotic syndrome. Shown are PRA and ANP concentration (+standard error) in normal persons ingesting diets high (300 mEq/d) and low (20 mEq/d) in sodium (Na) and in patients with acute glomerulonephritis (AGN), predominantly poststreptococcal, or nephrotic syndrome (NS). Note that PRA is suppressed in patients with AGN to levels below those in normal persons on diets high in Na. PRA suppression suggests that primary renal NaCl retention plays an important role in the pathogenesis of volume expansion in AGN. Although plasma renin activity in patients with nephrotic syndrome is not suppressed to the same degree, the absence of PRA elevation in these patients suggests that primary renal Na retention plays a significant role in the pathogen-esis of Na retention in NS as well. (Data from Rodrigeuez-Iturbe and coworkers [71].)

FIGURE 2-38

Sites of sodium (Na) reabsorption along the nephron in control and nephrotic rats (induced by puromycin aminonucleoside [PAN]). The glomerular filtration rates (GFR) in normal and nephrotic rats are shown by the hatched bars. Note the modest reduction in GFR in the nephrotic group, a finding that is common in human nephrosis. Fractional reabsorption rates along the proximal tubule, the loop of Henle, and the superficial distal tubule are indicated. The fractional reabsorption along the collecting duct (CD) is estimated from the difference between the end distal and urine deliveries. The data suggest that the predominant site of increased reabsorption is the collecting duct. Because superficial and deep nephrons may differ in reabsorptive rates, these data would also be consistent with enhanced reabsorption by deep nephrons. Asterisk—data inferred from the difference between distal and urine samples. (Data from Ichikawa and coworkers [72].)

Fluid intake

Nonrenal fluid loss i

Net volume intake

Arterial pressure

Kidney volume output

Kidney volume output

Rate of change of extracellular fluid volume

T"

T"

ECF volume, L

Rate of change of extracellular fluid volume

Extracellular fluid volume

Total peripheral resistance

ECF volume, L

Extracellular fluid volume

Blood volume

Blood volume

Cardiac output

Venous return

I Mean circulatory I filling pressure

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