Red blood cell Na+ transport as a predictor of blood pressure response to Na+ load in young blacks and whites

Electrolyte content of serum, erythrocyte, kidney and heart tissue in salt induced hypertensive rats

The effect of salt load on the systolic blood pressure (SBP) and electrolyte levels of serum, erythrocyte, kidney and heart tissue was studied in rats. NaCl treatment increased sodium (5.69 +/- 0.4 mmol/L p < 0.001, 149.8 +/- 4.0 mEq/L, p < 0.001) and decreased potassium (112.6 +/- 2.4 mmol/L p < 0.001, 5.0 +/- 0.2 mEq/L, p < 0.001) in red cell and serum respectively. A decreased level of serum magnesium (1.4 +/- 0.3 mEq/L, p < 0.005) was observed. Sodium content was increased in both heart (39.93 +/- 2.9 mumol/g, p = n.s) and kidney tissues (44.39 +/- 0.5 mumol/g, p < 0.001). A pronounced increase in intracellular calcium (2.54 +/- 0.2 mumol/g, p < 0.001) and a decrease of magnesium content (6.05 +/- 0.8 mumol/g, p < 0.001) was observed in kidney tissue after treatment. The results suggested that marked changes in electrolyte levels of erythrocytes, serum, heart and kidney tissues in NaCl loaded rats may play a definite role in the development of salt induced hypertension.

The link between hypertension and nephrosclerosis

Nephrosclerosis is literally defined as hardening of the kidneys (Greek derivation: nephros, kidney; sklerosis, hardening). It is the result of scarring or replacement of the normal renal parenchyma by dense collagenous tissue. In practice, nephrosclerosis refers to diseases with predominant pathologic changes occurring in the preglomerular microvasculature and secondarily involving the glomeruli and interstitium. The relationship between mild to moderate hypertension and either nephrosclerosis or end-stage renal disease (ESRD) remains circumstantial, although these syndromes have long been associated in the medical literature. Nephrologists credit hypertension as the etiology of nephrosclerosis in 25% of patients initiating Medicare-supported renal replacement therapy, even though other processes may cause similar renal pathologic findings. Strikingly, serum creatinine values infrequently increase in patients with long-standing mild to moderate hypertension. Patients classified as having hypertensive ESRD typically present with advanced disease, making the processes that initiated the renal disease difficult to detect. Nephrologists are twice as likely to label an African-American patient as having hypertensive nephrosclerosis, compared with a white patient, when presented with identical clinical histories. This review proposes that many patients classified as having hypertensive nephrosclerosis actually have intrinsic renal parenchymal diseases, renal artery stenosis, unrecognized episodes of accelerated hypertension, or a primary renal microvascular disease. The familial clustering of ESRD attributed to hypertension in African-Americans and the identification of genes associated with renal injury in animals support the concept that inherited factors may predispose to renal failure. African-American families often have members with ESRD from disparate etiologies, including hypertensive ESRD. This suggests that common mechanisms, be they inherited or environmental, underlie the development of progressive renal failure in diverse forms of nephropathy. Identification of the mechanisms producing susceptibility to progressive renal disease would support the concept that mild to moderate elevations in blood pressure per se are uncommon causes of nephrosclerosis.

Renal apical membrane sodium-hydrogen exchange in genetic salt-sensitive hypertension

Inbred Dahl/Rapp salt-sensitive and salt-resistant rats differ in their blood pressure response to dietary salt. We studied sodium-hydrogen (Na-H) exchanger kinetics in renal brush border membrane vesicles prepared from both strains on either a 1% or 8% NaCl diet. Kinetics measurements were made with the acridine orange fluorescence quenching technique in vesicles prepared at pH 6.0. The initial Na-H exchange rate was measured using preparations with similar initial quench values. The maximal transport rate (Vmax, fluorescence units per second per milligram protein [+/- SEM]) in salt-sensitive rats on a 1% NaCl diet was significantly lower than that in salt-resistant rats (36.9 +/- 4.4 versus 51.8 +/- 5.5, respectively, P < .0005). With the 8% NaCl diet for 1 week, the Vmax of salt-resistant rats decreased and became similar to that of salt-sensitive rats. The affinity for sodium (Km, millimoles per liter [+/- SEM]) was also lower in salt-sensitive rats than in salt-resistant rats while on a 1% NaCl diet (11.8 +/- 1.0 versus 19.6 +/- 2.3, respectively, P < .002). These values converged when both strains were fed an 8% NaCl diet for 1 week. Inhibition by 25 mumol/L amiloride was less in salt-sensitive rats than in salt-resistant rats on the 1% NaCl diet. These results show that salt-sensitive rats have lower renal apical membrane Na-H exchange activity than salt-resistant rats on a 1% NaCl diet.(ABSTRACT TRUNCATED AT 250 WORDS)

Intracellular ionic consequences of dietary salt loading in essential hypertension. Relation to blood pressure and effects of calcium channel blockade

To study the ionic basis of salt sensitivity in hypertension, 19F-, 13P-, and 23Na-nuclear magnetic resonance techniques were used to measure cytosolic free calcium (Cai), pH (pHi), free magnesium (Mgi), and sodium (Nai) in erythrocytes of essential hypertensive subjects (n = 19). Individuals were studied for 2 mo each on low- (UNaV < 50 meq/d) and high- (UNaV > 200 meq/d) salt diets, with the concomitant administration of nifedipine (10 mg t.i.d.) or placebo tablets for 1 mo of each diet. Salt loading elevated Cai and Nai while suppressing Mgi and pHi; these changes occurred predominantly in salt-sensitive subjects (n = 9). Nifedipine blunted the pressor response to salt loading > 50% (delta diastolic BP [high-low salt vs placebo] = 5 +/- 2 vs 14 +/- 2 mmHg, P < 0.05) and reversed salt-induced ionic changes, lowering Cai and elevating Mgi and pHi. Regardless of the definition of salt sensitivity, continuous relationships were observed between the pressure response to salt loading, the levels of Cai (r = 0.726, P < 0.001), Nai (r = 0.747, P < 0.001), and pHi (r = -0.754, P < 0.001), and the salt-induced change in Mgi (r = -0.757, P < 0.001). Altogether, these results emphasize the reciprocal and coordinate nature of intracellular ionic changes in response to dietary salt loading and calcium channel blockade in essential hypertension. They suggest that salt sensitivity is mediated by cellular calcium accumulation from the extracellular space, in association with magnesium depletion and acidification. Lastly, interpretation of intracellular ion measurements in the future will require concurrent assessment of dietary salt intake.

Impact of malaria on genetic polymorphism and genetic diseases in Africans and African Americans

The high mortality from malaria in sub-Sahara Africa selected multiple genes that give the population a selective advantage. Identification of the genetic basis for resistance may suggest unusual approaches to development of malarial vaccines and antimalarial drugs. Some of these genes may be deleterious, although of selective advantage within the African setting, and need to be identified for counseling for disease prevention.

The familial risk of end-stage renal disease in African Americans

African Americans have higher overall incidence rates of end-stage renal disease (ESRD) compared with American whites. Hypertensive nephrosclerosis (HN), nephropathy secondary to diabetes mellitus types I and II, and chronic glomerulonephritis (CGN) all occur more frequently in African Americans. To explore the possibility that hereditary factors may play a role in the increased risk of ESRD in African Americans, the family history of 131 African American hemodialysis patients (cases) was compared with 115 age-, sex-, and race-matched non-ESRD controls. Odds ratios (ORs) were calculated to define the prevalence of a relative with ESRD among cases versus controls. Chi-square values were estimated from a log-linear model, while controlling for gender, to test for significance of ORs. Forty percent (12/30) of HN cases, 35% (18/51) of type II diabetes mellitus-induced renal failure cases, and 13% (5/38) of CGN cases had a first-, second-, or third-degree relative with ESRD. The presence of a first-degree relative with ESRD increased an African American's risk for developing ESRD ninefold (OR, 9.13; 95% confidence interval [CI], 2.6 to 31.8; P < 0.001). The presence of a first- or second-degree relative increased the risk fivefold (OR, 5.23; 95% CI, 2.2 to 12.3; P < 0.0002). First-, second-, or third-degree relatives with ESRD were more prevalent among cases with ESRD due to hypertension and type II diabetes mellitus compared with CGN (P < or = 0.05). Gender differences among the ORs were nonsignificant (P > 0.2) and socioeconomic class (level of education and income) did not differ markedly between cases and controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Definitions and characteristics of salt-sensitivity and resistance of blood pressure: should the diagnosis depend on diastolic blood pressure?

To elucidate the importance of diastolic blood pressure in the definition of salt-sensitive hypertension, we studied 54 male subjects, 36 of whom had untreated, mild essential hypertension. The subjects received a 120 mmol/d Na (as the chloride salt) diet for six days. Thereafter they received a 10 mmol/d Na diet for eight days followed by a 400 mmol/d Na diet for another 8 days. Blood pressure was measured hourly "around the clock" on the last day of each diet; the averaged systolic, diastolic and mean blood pressure values were compared. In 22 subjects diastolic blood pressure increased, when salt intake was increased from 10 to 400 mmol/d. In 18 of these 22 subjects systolic blood pressure increased as well. In 20 subjects, systolic blood pressure increased with salt loading while diastolic blood pressure decreased. In 13 subjects both systolic and diastolic blood pressure decreased with increased salt intake. We defined those subjects showing an increase in diastolic blood pressure as salt-sensitive. If mean blood pressure were used to define salt-sensitivity, 8 of our subjects would have been labeled as salt-sensitive who actually decreased their diastolic blood pressure with salt loading. We suggest that consideration of systolic and diastolic blood pressure responses gives better insight into identifying volume and resistance-related phenomena in salt-sensitive hypertension, than does the consideration of mean blood pressure alone. The definition of salt-sensitivity may require reassessment.