Renal acid excretion and intracellular pH in salt-sensitive genetic hypertension

Serum Untargeted Metabolism Reveals the Mechanism of L. plantarum ZDY2013 in Alleviating Kidney Injury Induced by High-Salt Diet

A high-salt diet (HSD) is one of the key risk factors for hypertension and kidney injury. In this study, a HSD C57BL/6J mice model was established with 4% NaCl, and then different concentrations of Lactobacillus plantarum ZDY2013 were intragastrically administered for 2 weeks to alleviate HSD-induced renal injury. For the study, 16S rRNA gene sequencing, non-targeted metabonomics, real-time fluorescent quantitative PCR, and Masson’s staining were used to investigate the mechanism of L. plantarum ZDY2013 in alleviating renal damage. Results showed that HSD caused intestinal inflammation and changed the intestinal permeability of mice, disrupted the balance of intestinal flora, and increased toxic metabolites (tetrahydrocorticosteron (THB), 3-methyhistidine (3-MH), creatinine, urea, and L-kynurenine), resulting in serious kidney damage. Interestingly, L. plantarum ZDY2013 contributed to reconstructing the intestinal flora of mice by increasing the level of Lactobacillus and Bifidobacterium and decreasing that of Prevotella and Bacteroides. Moreover, the reconstructed intestinal microbiota significantly changed the concentration of the metabolites of hosts through metabolic pathways, including TCA cycle, ABC transport, purine metabolism, and histidine metabolism. The content of uremic toxins such as L-kynurenine, creatinine, and urea in the serum of mice was found to be decreased by L. plantarum ZDY2013, which resulted in renal injury alleviation. Our data suggest that L. plantarum ZDY2013 can indeed improve chronic kidney injury by regulating intestinal flora, strengthening the intestinal barrier, limiting inflammatory response, and reducing uremic toxins.

Elevated hypertension risk associated with higher dietary acid load: A systematic review and meta-analysis

BACKGROUND & AIMS

The association between dietary acid load and hypertension risk is inconclusive. We conducted a systematic review and meta-analysis to summarize effect of dietary acid load on blood pressure.

METHODS

A comprehensively search was performed in electronic databases including EMBASE, PubMed, Web of Science and Chinese National Knowledge Infrastructure. Summary ORs and their corresponding 95% CIs were computed assuming a randomized model or fixed model.

RESULTS

Ten publications comprising 4 cohort and 6 cross-sectional studies were eligible for meta-analysis. There were 8 studies about potential renal acid load (PRAL) and 4 about net endogenous acid production (NEAP). Essential hypertension was statistically associated with higher PRAL (OR = 1.14, 95% CI = 1.02-1.17). Our findings also demonstrated a positive impact of higher PRAL on elevating both diastolic pressure (WMD = 0.96, 95% CI = 0.67-1.26) and systolic pressure (WMD = 1.57, 95% CI = 1.12-2.03). A 35% increased risk of hypertension associated with higher NEAP was identified (OR = 1.35, 95% CI = 1.03-1.78).

CONCLUSIONS

The current study suggests that dietary acid load might be potential risk factor of hypertension.

Dietary acid load, kidney function and risk of chronic kidney disease: A systematic review and meta-analysis of observational studies

Aim: Study findings examining the association between dietary acid load (DAL), kidney function and risk of chronic kidney disease (CKD) are inconsistent and there has been no meta-analysis on the relationship between DAL, kidney function and risk of CKD, hence we investigated this association in this paper. Methods: PubMed, ISI web of science and Scopus were searched up to January 2018 to identify all relevant articles. Effect sizes of eligible studies were pooled in random- effect model using the Der Simonian-Laird method. The I² index was used to assess the amount of heterogeneity. Result: Twenty three studies with 200092 subjects were included. Meta-analysis of 9 observational studies showed that DAL had a positive significant association with risk of CKD (1.31; 95% CI: 1.06, 1.62; P = 0.011). Furthermore, increased DAL can decrease urine pH (-0.47; 95% CI: -0.85, -0.08; P = 0.017) significantly. Subgroup analysis could not identify the sources of heterogeneity about the association of DAL and risk of CKD. However, it showed the method of measurement was the source of heterogeneity about the association of DAL and urine pH (24 h urine pH: -0.62; 95% CI: -0.70, -0.54; P < 0.0001; Fasting urine pH: -0.08; 95% CI: -0.18, 0.02; P = 0.111). Conclusion: Our study showed that DAL can increase the risk of CKD and have an inverse association with urine pH.

Urinary pH reflects dietary acid load in patients with type 2 diabetes

Dietary acid load is important information, however, survey of food intake needs time and skill. Therefore, it is difficult to survey food intake from all patients. It remains to be elucidated the association between dietary acid load and urinary pH in patients with type 2 diabetes. In this cross-sectional study of 173 patients, we investigated the relationship between urinary pH and dietary acid load, assessed with potential renal acid load. Habitual food and nutrient intake was assessed by a self-administered diet history questionnaire. Urinary pH was negatively correlated with potential renal acid load (r = –0.24, p = 0.002). Multivariate regression analysis revealed that potential renal acid load (standardized regression coefficient = –0.21, p = 0.036) was associated with urinary pH after adjusting for covariates. In addition, according to the receiver operator characteristic analysis, the optimal cut-off point of urinary pH for high dietary acid load, defined as potential renal acid load over 7.0 mEq/day was 5.7 (area under the receiver operator characteristic curve 0.63 (95% CI 0.54–0.71), sensitivity = 0.56, specificity = 0.70, p = 0.004). Urinary pH was associated with dietary acid load in patients with type 2 diabetes. We suggest that urinary pH can be a practical screening marker for dietary acid load in patients with type 2 diabetes.

Proton channels and renal hypertensive injury: a key piece of the Dahl salt-sensitive rat puzzle?

Hv1 is a voltage-gated proton channel highly expressed in phagocytic cells, where it participates in the NADPH oxidase-dependent respiratory burst. We have recently identified Hv1 as a novel renal channel, expressed in the renal medullary thick ascending limb that appears to importantly contribute to the pathogenesis of renal hypertensive injury in the Dahl salt-sensitive rat model. The purpose of this review is to describe the experimental approaches that we have undertaken to identify the source of excess reactive oxygen species production in the renal outer medulla of Dahl salt-sensitive rats and the resulting evidence that the voltage-gated proton channel Hv1 mediates augmented superoxide production and contributes to renal medullary oxidative stress and renal injury. In addition, we will attempt to point out areas of current controversy, as well as propose areas in which further experimental studies are likely to move the field forward. The content of the following review was presented as part of the Water and Electrolyte Homeostasis Section New Investigator Award talk at Experimental Biology 2014.

Metabolic syndrome and nephrolithiasis

Problem

This review focuses on the association between the metabolic syndrome (MS) and nephrolithiasis.

Findings

Associations between nephrolithiasis and systemic diseases are recognized, including atherosclerosis, cardiovascular (CV) disease, hypertension (HNT), diabetes mellitus (DM)—composite risk factors grouped as the MS. Kidney stones incidence is increasing in this particularly high risk group. Those with stones are prone to the disease and those with the systemic disease are at risk for stone formation, with the highest incidence in persons with multiple traits of the MS. Pathophysiologic explanations for the increased stone risk related to MS are likely complex and dynamic.

Conclusions

Kidney stones disproportionately affect persons with some or all traits of MS. One unifying theory may be of a common systemic malfunction of inflammation and tissue damage as an underlying mechanism, but it is unlikely to be the only mechanistic explanation. Further research is needed to investigate this and other hypotheses that go beyond population based and urine physiochemical studies in order to elucidate the mechanisms behind the individual disease states themselves.

Estimated dietary acid load is not associated with blood pressure or hypertension incidence in men who are approximately 70 years old

BACKGROUND

Dietary acid load affects acid-base homeostasis, which may be associated with blood pressure (BP). Previous research on dietary acid load and BP in the community has provided conflicting results, which may be confounded by underlying kidney function with inability to eliminate acid excess.

OBJECTIVE

The objective of this study was to determine whether dietary acid load is associated with blood pressure or the incidence of hypertension in older men taking into account each individual's kidney function.

METHODS

We included 673 men aged 70-71 y and not receiving antihypertensive medication from the Uppsala Longitudinal Study of Adult Men. Of those, 378 men were re-examined after 7 y. Dietary acid load was estimated at baseline by potential renal acid load (PRAL) and net endogenous acid production (NEAP), based on nutrient intake assessed by 7-d food records at baseline. Ambulatory blood pressure monitoring (ABPM) was performed at both visits. Cystatin C-estimated kidney function allowed identification of underlying chronic kidney disease.

RESULTS

Median estimated PRAL and NEAP were 3.3 and 40.7 mEq/d, respectively. In cross-section, PRAL was in general not associated with ABPM measurements (all P > 0.05, except for the 24-h diastolic BP). During follow-up, PRAL did not predict ABPM changes (all P > 0.05). When individuals with baseline hypertension (ABPM ≥ 130/80 mm Hg) or nondippers (with nighttime-to-daytime systolic BP ratio > 0.9) were excluded, PRAL was not a predictor of incident cases (P > 0.30). Kidney function did not modify these null relations. Similar findings were obtained with the use of NEAP as the exposure.

CONCLUSION

Our analyses linking estimated dietary acid load with BP outcome measurements both cross-sectionally and after 7 y in community-based older Swedish men of similar age did not reveal an association between dietary acid load and BP.

HV1 acts as a sodium sensor and promotes superoxide production in medullary thick ascending limb of Dahl salt-sensitive rats

We previously characterized a H(+) transport pathway in medullary thick ascending limb nephron segments that when activated stimulated the production of superoxide by nicotinamide adenine dinucleotide phosphate oxidase. Importantly, the activity of this pathway was greater in Dahl salt-sensitive rats than salt-resistant (SS.13(BN)) rats, and superoxide production was enhanced in low Na(+) media. The goal of this study was to determine the molecular identity of this pathway and its relationship to Na(+). We hypothesized that the voltage-gated proton channel, HV1, was the source of superoxide-stimulating H(+) currents. To test this hypothesis, we developed HV1(-/-) null mutant rats on the Dahl salt-sensitive rat genetic background using zinc-finger nuclease gene targeting. HV1 could be detected in medullary thick limb from wild-type rats. Intracellular acidification using an NH4Cl prepulse in 0 sodium/BaCl2 containing media resulted in superoxide production in thick limb from wild-type but not HV1(-/-) rats (P<0.05) and more rapid recovery of intracellular pH in wild-type rats (ΔpHI 0.005 versus 0.002 U/s, P=0.046, respectively). Superoxide production was enhanced by low intracellular sodium (<10 mmol/L) in both thick limb and peritoneal macrophages only when HV1 was present. When fed a high-salt diet, blood pressure, outer medullary renal injury (tubular casts), and oxidative stress (4-hydroxynonenal staining) were significantly reduced in HV1(-/-) rats compared with wild-type Dahl salt-sensitive rats. We conclude that HV1 is expressed in medullary thick ascending limb and promotes superoxide production in this segment when intracellular Na(+) is low. HV1 contributes to the development of hypertension and renal disease in Dahl salt-sensitive rats.

Sensory renal innervation: a kidney-specific firing activity due to a unique expression pattern of voltage-gated sodium channels?

Sensory neurons with afferent axons from the kidney are extraordinary in their response to electrical stimulation. More than 50% exhibit a tonic firing pattern, i.e., sustained action potential firing throughout depolarizing, pointing to an increased excitability, whereas nonrenal neurons show mainly a phasic response, i.e., less than five action potentials. Here we investigated whether these peculiar firing characteristics of renal afferent neurons are due to differences in the expression of voltage-gated sodium channels (Navs). Dorsal root ganglion (DRG) neurons from rats (Th11-L2) were recorded by the current-clamp technique and distinguished as "tonic" or "phasic." In voltage-clamp recordings, Navs were characterized by their tetrodotoxoxin (TTX) sensitivity, and their molecular identity was revealed by RT-PCR. The firing pattern of 66 DRG neurons (41 renal and 25 nonrenal) was investigated. Renal neurons exhibited more often a tonic firing pattern (56.1 vs. 12%). Tonic neurons showed a more positive threshold (-21.75 ± 1.43 vs.-29.33 ± 1.63 mV; P < 0.05), a higher overshoot (56.74 [53.6-60.96] vs. 46.79 mV [38.63-54.75]; P < 0.05) and longer action potential duration (4.61 [4.15-5.85] vs. 3.35 ms [2.12-5.67]; P < 0.05). These findings point to an increased presence of the TTX-resistant Navs 1.8 and 1.9. Furthermore, tonic neurons exhibited a relatively higher portion of TTX-resistant sodium currents. Interestingly, mRNA expression of TTX-resistant sodium channels was significantly increased in renal, predominantly tonic, DRG neurons. Hence, under physiological conditions, renal sensory neurons exhibit predominantly a firing pattern associated with higher excitability. Our findings support that this is due to an increased expression and activation of TTX-resistant Navs.

No evidence that the skeletal non-response to potassium alkali supplements in healthy postmenopausal women depends on blood pressure or sodium chloride intake

BACKGROUND/OBJECTIVES

In vitro studies demonstrate that bone is degraded in an acidic environment due to chemical reactions and through effects on bone cells. Clinical evidence is insufficient to unequivocally resolve whether the diet net acid or base load bone affects breakdown in humans. Increasing dietary salt (sodium chloride, NaCl) mildly increases blood acidity in humans and in rats with increased sensitivity to the blood pressure effects of salt, whereas increased potassium (K) intake can decrease blood pressure. Blood pressure responses to NaCl or K may potentially be a marker for increased bone turnover or lower bone mineral density (BMD) in women at higher risk for osteoporosis and fracture.

SUBJECTS/METHODS

We retrospectively analysed data from two data sets (California and NE Scotland) of postmenopausal women (n=266) enrolled in long-term randomized, placebo-controlled studies of the effects of administration of low- or high-dose dietary K alkali supplementation on bone turnover in relation to sodium or chloride excretion (a marker of dietary salt intake). Mean arterial pressure (MAP) was calculated from blood pressure measures, MAP was divided into tertiles and its influence on the effect of dietary NaCl and K alkali supplementation on deoxypyridinoline markers of bone resorption and BMD by DEXA was tested. Data was analysed for each data set separately and then combined.

RESULTS

Percentage change in BMD after 24 months was less for California compared with North East Scotland (hip: -0.6 ± 2.8% and -1.5 ± 2.4%, respectively (P=0.027); spine: -0.5 ± 3.4% and -2.6 ± 3.5%, (P<0.001). We found no effect of dietary alkali treatment on BMD change or bone resorption for either centre. Adjusting for the possible calcium- or potassium-lowering effects on blood pressure did not alter the results.

CONCLUSIONS

Blood pressure responses to Na, Cl or K intake did not help predict a BMD response to diet alkali therapy.

Lower serum bicarbonate and a higher anion gap are associated with lower cardiorespiratory fitness in young adults

Lower levels of serum bicarbonate and a higher anion gap have been associated with insulin resistance and hypertension in the general population. Whether these associations extend to other cardiovascular disease risk factors is unknown. To clarify this, we examined the association of serum bicarbonate and anion gap with cardiorespiratory fitness in 2714 adults aged 20–49 years in the 1999–2004 National Health and Nutrition Examination Survey. The mean serum bicarbonate was 24.6 mEq/L and the mean anion gap was 10.26 mEq/L, with fitness determined by submaximal exercise testing. After multivariable adjustment, gender, length of fasting, soft drink consumption, systolic blood pressure, serum phosphate, and hemoglobin were independently associated with both the serum bicarbonate and the anion gap. Low fitness was most prevalent among those in the lowest quartile of serum bicarbonate or highest quartile of anion gap. After multivariable adjustment, a one standard deviation higher serum bicarbonate or anion gap was associated with an odds ratio for low fitness of 0.80 (95% CI 0.70–0.91) and 1.30 (95% CI 1.15–1.48), respectively. The association of bicarbonate with fitness may be mediated by differences in lean body mass. Thus, lower levels of serum bicarbonate and higher levels of anion gap are associated with lower cardiorespiratory fitness in adults aged 20–49 years in the general population.

Updated epidemiologic study of urolithiasis in Turkey II: role of metabolic syndrome components on urolithiasis

The components of metabolic syndrome, such as obesity, hypertension, and diabetes, are thought to be associated with urolithiasis. However, there are few large-scale studies that have examined the association between metabolic syndrome and urolithiasis, which prompted us to study and evaluate the relationship between metabolic syndrome components and urolithiasis in a nationwide survey, using the cross-sectional study conducted by a professional investigation company, with 2,468 enrolled participants, aged between 18 and 70 years, from 33 provinces in Turkey. Participants were interviewed face-to-face by medical faculty students. Participants with a history of urolithiasis (Group 1) were compared with participants without a history of urolithiasis (Group 2) in terms of hypertension, diabetes, body-mass index (BMI), waist size, and trouser size using Chi-square and odds ratio tests. Of the 2,468 participants, 274 (11.1%) reported a history of urinary stone disease diagnosed by a physician. The percentage of participants with hypertension along with urolithiasis was significantly higher than that in participants without urolithiasis (16.9 and 34.3%, p 0.000, OR 3.0). The percentage of participants with diabetes in groups 1 and 2 was 14.2 and 9%, respectively (p 0.001, OR 1.83). The mean BMI was 27.2 and 25.2, respectively (p 0.01). Participants with a BMI >30 had a 2.2-fold increased risk of having urolithiasis. The mean waist size was significantly greater in participants with urolithiasis (p 0.000). Those with a waist size >100 cm had a 1.87-fold increased risk of having urolithiasis. The mean trouser size was also significantly larger in those participants who were stone formers (p 0.003). The results indicate that metabolic syndrome components are important factors in the development of urolithiasis.

Hypertension is associated with increased urinary calcium excretion in patients with nephrolithiasis

PURPOSE

The epidemiological relationship between nephrolithiasis and hypertension is well-known. Patients with hypertension are at increased risk for nephrolithiasis and those with nephrolithiasis are at risk for hypertension. Urine calcium or urine citrate may be related to hypertension status. We examined the relationship between hypertension and 24-hour urine composition in patients with nephrolithiasis.

MATERIALS AND METHODS

We retrospectively reviewed the database on 462 stone forming patients to examine the relationship between hypertension and 24-hour urine composition. Multivariate linear regression models were adjusted for age, race, gender, body mass index, diabetes mellitus and 24-hour urine constituents. Nominal logistic regression was also done to examine the hypertension prevalence by quintile of calcium and citrate excretion.

RESULTS

On adjusted multivariate analysis compared with normotensive stone formers those with hypertension excreted 25.6 mg per day more urine calcium, corresponding to a 12% increase in urinary calcium excretion. The relative risk of hypertension was significantly associated with quintile of calcium excretion but not with quintile of citrate excretion (1.29, 95% CI 1.02 to 1.61 vs 0.94, 95% CI 0.78 to 1.14).

CONCLUSIONS

In stone formers hypertension was associated only with significantly increased urine calcium. This association is important when treating patients with nephrolithiasis since those with hypertension may require unique dietary and medical therapy.

Diet-dependent net acid load and risk of incident hypertension in United States women

Animal and human studies suggest a potential link between acid-base status and blood pressure. Contemporary Western diets yield a daily systemic acid load of varying amounts, yet the association with hypertension has never been explored. We prospectively examined the association between the diet-dependent net acid load (also known as the estimated net endogenous acid production) and the risk of incident hypertension among 87 293 women without a history of hypertension in the Nurses' Health Study II. We also used the ratio of animal protein intake to potassium intake as an alternative evaluation of diet-dependent net acid load. We identified 15 385 incident cases of hypertension during 995 239 person-years of follow-up. After adjusting for potential confounders, women in the top decile of estimated diet-dependent net acid load had an increased risk of hypertension (relative risk: 1.14; 95% CI: 1.05 to 1.24; P for trend=0.01) compared with women in the bottom decile. To test whether the association between estimated diet-dependent net acid load and hypertension is independent of its individual components, an additional adjustment for intakes of protein and potassium was made and resulted in a relative risk of 1.23 (95% CI: 1.08 to 1.41; P for trend=0.003) for the top decile of estimated diet-dependent net acid load. Results of the ratio of animal protein intake to potassium intake were similar with those of estimated diet-depend net acid load. In conclusion, a high diet-dependent net acid load is independently associated with a higher risk of incident hypertension.

Nephrolithiasis as a systemic disorder

PURPOSE OF REVIEW

Nephrolithiasis is a prominent public health issue. It imposes a substantial burden on human health and is a considerable financial expenditure for the nation. Numerous epidemiologic studies have shown a significant association between nephrolithiasis, obesity, hypertension and chronic kidney disease. The review highlights many of those emerging studies and sheds light on the importance of our recognition of kidney stones as a systemic illness.

RECENT FINDINGS

Several cross-sectional retrospective studies have investigated the relationship between kidney stones and the metabolic syndrome. The various silent features of the metabolic syndrome, including type 2 diabetes, increased BMI, hypertension and dyslipidemia, are becoming progressively more recognized and independently associated with an increased risk of kidney stone formation.

SUMMARY

Our further understanding of the underlying mechanisms in the connection between nephrolithiasis and the metabolic syndrome will stimulate the development of more effective preventive and therapeutic measures.

Increased acid excretion in kidney stone formers with essential hypertension

BACKGROUND

Although several studies have reported that kidney stone disease and hypertension are associated, the link between the two conditions has not been identified. This study investigated urinary excretion of different solutes, particularly citrate and acids, in kidney stone formers and examined their association with high blood pressure.

METHODS

The retrospective study included 234 consecutive subjects, aged 47.0 +/- 15.6, attending our metabolic clinic after episodes of kidney stones. Essential hypertension was present in 82 patients (35.0%). A difference in the urinary excretion of some of the investigated components was found between subjects with normal blood pressure and those with hypertension.

RESULTS

The results showed that hypertensive subjects were older and had a higher body mass index (BMI) and serum uric acid. They had a significantly lower urinary pH (5.6 +/- 0.4 versus 6.0 +/- 0.5) and citrate (2.55 +/- 1.36 versus 2.83 +/- 1.65 mmol/24 h), higher titratable acid (38.8 +/- 19.0 versus 26.8 +/- 15.0 mEq/24 h) and ammonium (41.6 +/- 17.6 versus 34.2 +/-12.4 mmol/24 h). Logistic regression analysis with the presence of hypertension as the dependent variable produced a model with the following predictors: age (P < 0.0001), BMI (P = 0.026), titratable acid (P = 0.025) and low urinary citrate level (P = 0.033). Urinary acid excretion increased with the stage of hypertension. No difference was found in the urinary excretion of other solutes.

CONCLUSIONS

These findings suggest that essential hypertension and acid excretion are linked in stone formers.

The association of nephrolithiasis with hypertension and obesity: a review

Kidney stones affect hypertensive patients disproportionately compared to normotensive individuals. On the other hand, some prospective data suggest that a history of nephrolithiasis was associated with a greater tendency to develop hypertension. Newer epidemiologic data also link obesity and diabetes, features of the metabolic syndrome, with nephrolithiasis. In this review, the association of hypertension, diabetes, and obesity with nephrolithiasis is reviewed, and possible pathogenic mechanisms are discussed. Patients with hypertension may have abnormalities of renal calcium metabolism, but data confirming this hypothesis are inconsistent. Higher body mass index and insulin resistance (i.e., the metabolic syndrome) may be etiologic in uric acid nephrolithiasis as increasing body weight is associated with decreasing urinary pH. The possibility that common pathophysiologic mechanisms underly these diseases is intriguing, and if better understood, could potentially lead to better therapies for stone prevention. Both hypertension and stones might be addressed through lifestyle modification to prevent weight gain. Adoption of a lower sodium diet with increased fruits and vegetables and low-fat dairy products, (for example, the dietary approaches to stop hypertension(DASH) diet), may be useful to prevent both stones and hypertension. In those patients in whom dietary modification and weight loss are ineffective, thiazide diuretics are likely to improve blood pressure control and decrease calciuria.

Association between the serum anion gap and blood pressure among patients at Harvard Vanguard Medical Associates

Animal and human data suggest a link between endogenous acid production with elevations in blood pressure and the development of hypertension; increases in endogenous organic acid production can lead to a higher anion gap. We studied the cross-sectional association between the serum anion gap and blood pressure among 1057 non-diabetic patients who were not taking antihypertensive drugs, and who received their care at a multisite, multispecialty group practice in eastern Massachusetts. Using linear regression controlling for age, sex, race, BMI, estimated GFR and presence of impaired fasting glucose, every 1 mEq l(-1) higher serum anion gap was associated with a 0.27 mm Hg (P=0.08) higher systolic, 0.20 mm Hg (P=0.05) higher diastolic and 0.22 mm Hg (P=0.04) higher mean arterial pressure; these results suggest that endogenous acid production may raise the risk of hypertension.

Serum Anion Gap and Blood Pressure in the National Health and Nutrition Examination Survey

Increased production of organic acid can result in an elevated serum anion gap and may play a role in the development of hypertension. We studied the cross-sectional associations between anion gap and blood pressure and between serum bicarbonate and blood pressure in the 1999-2000 and 2001-2002 National Health and Nutrition Examination Surveys. We included 5043 adult participants who were not taking antihypertensive medications or diuretics and who denied hypertension, cardiovascular disease, diabetes, and other diseases. Linear regression was used to adjust for age, race, body mass index, creatinine, albumin, and other factors. Sample weights were used to produce weighted regression parameters. In the lowest quintile of anion gap, mean values of sodium, chloride, and bicarbonate were 139 mEq/L, 105 mEq/L, and 25 mEq/L, respectively. In the highest quintile, mean values of sodium, chloride, and bicarbonate were 140 mEq/L, 101 mEq/L, and 22 mEq/L, respectively. Mean blood pressure was 118/72 mm Hg. After multivariable adjustment, participants in the highest quintile of anion gap had systolic blood pressure 3.73 mm Hg higher (95% CI: 1.83 to 5.63 mm Hg; P for trend: <0.01) than participants in the lowest quintile. Participants in the highest quintile of bicarbonate had systolic blood pressure 2.73 mm Hg lower (95% CI: 1.26 to 4.20 mm Hg; P for trend: <0.01) than participants in the lowest quintile. No associations were observed between anion gap or bicarbonate and diastolic blood pressure. The results were unchanged after excluding participants with estimated glomerular filtration rate <60 cc/min per 1.73 m(2). The anion gap is independently associated with higher blood pressure. Further research is needed to elucidate the relation between organic acid and hypertension.

Association of prevalent hypertension with 24-hour urinary excretion of calcium, citrate, and other factors

BACKGROUND

The relation between hypertension and the urinary excretion of calcium, citrate, and other factors is unclear. It has been proposed that increased urinary calcium excretion is a central feature of essential hypertension. Metabolic acidosis also may be associated with hypertension and decreases urinary citrate levels.

METHODS

To compare the urine composition of individuals with and without hypertension, we studied 24-hour urinary excretion of calcium, citrate, oxalate, uric acid, sodium, magnesium, potassium, phosphorus, and creatinine and pH in a subset of participants with and without nephrolithiasis in the Nurses' Health Study I (older women; N = 1,284), Nurses' Health Study II (younger women; N = 952), and the Health Professionals Follow-up Study (men; N = 788). Logistic regression models adjusted for age, weight, dietary intake, and urinary factors.

RESULTS

In participants with and without nephrolithiasis, citrate was the only urinary factor consistently related to hypertension. Compared with those in the lowest quartile of urinary citrate excretion, multivariate odds ratios of prevalent hypertension in the highest quartile were 0.37 (95% confidence interval [CI], 0.24 to 0.55; P trend < 0.001) for older women, 0.54 (95% CI, 0.32 to 0.92; P trend = 0.03) for younger women, and 0.27 (95% CI, 0.16 to 0.45; P trend < 0.001) for men. Urinary calcium levels were not related consistently to hypertension. Excluding participants with single 24-hour urine collections and those administered thiazide diuretics or angiotensin-converting enzyme inhibitors did not change the results.

CONCLUSION

Lower urinary citrate excretion is associated independently with prevalent hypertension. Factors that regulate urinary citrate excretion may play a role in hypertension.

Localization of a blood pressure QTL to a 2.4-cM interval on rat chromosome 9 using congenic strains

A blood pressure (BP) quantitative trait locus (QTL) was previously found on rat chromosome 9 using Dahl salt-sensitive (S) and Dahl salt-resistant (R) rats. A congenic strain, S.R(chr9), constructed by introgressing an R chromosomal segment into the S background, previously proved the existence of a BP QTL in a large 34.2-cM segment of chromosome 9. In the current work congenic substrains were constructed from the progenitor congenic strain, S.R(chr9). BP and heart weight comparisons between these congenic substrains and their S control localized the BP QTL to a 4.6-cM interval. Two solute carrier (Na(+)/H(+) exchanger) genes, Nhe2 and Nhe4, were excluded as candidates based on their map locations. A second iteration of congenic substrains was used to localize the QTL further to a 2.4-cM interval. Another solute carrier (Cl(-)/HCO3- exchanger) gene, Ae3, is in this reduced interval and was sequenced for both S and R strains, but no coding sequence variations were found. Ae3 mRNA was not differentially expressed in the kidney of congenic compared to S rats. Although the identity of the QTL remains unknown its map location has been reduced from an interval of 34.2 to 2.4 cM.

Racial differences in resting end-tidal CO2 and circulating sodium pump inhibitor

Previous studies have shown that high end-tidal CO2 (PetCO2) is a marker for sodium sensitivity of blood pressure (BP) in White Americans, and that the BP of African Americans is more sensitive to high sodium intake than that of whites. The present study tested the hypothesis that resting PetCO2 is higher in normotensive African Americans than in whites. Resting end-tidal CO2 of 395 white and 125 African American participants in the Baltimore Longitudinal Study on Aging was monitored for 20 min with a respiratory gas monitor, and BP and heart rate were recorded every 5 min by oscillometric methodology. Twenty-four-hour urinary excretion of a circulating sodium pump inhibitor marinobufagenin-like compound (MBG), which increases when plasma volume is expanded, was also analyzed by fluoroimmunoassay in racial groups. Mean resting PetCO2 of African American men was higher than that of white men (38.1+/-0.5 v 36.4+/-0.3 mm Hg), and resting PetCO2 of African American women was higher than that of white women (37.7+/-0.3 v 36.2+/-0.3 mm Hg). The differences were not significant in either men or women less than 50 years old, but were substantial in both men and women more than 50 years. Twenty-four-hour urinary excretion of MBG was higher in white (2.7+/-0.2 pmol) than in African American (2.1+/-0.2 pmol) participants, and high PetCO2 was a significant independent predictor of high MBG excretion in African Americans. These data are consistent with the hypothesis that the higher resting PetCO2 in African Americans plays a role in slower urinary excretion of sodium, greater BP sensitivity to high sodium intake, and increased prevalence of chronic hypertension.

The mechanism of action of angiotensin II is dependent on direct activation of vascular smooth muscle carbonic anhydrase I

Our previous studies have shown that angiotensin II increases carbonic anhydrase activity both in vitro and in vivo. In this study we investigated in vitro the effect of angiotensin II on carbonic anhydrase I and II from erythrocytes and on arteriolar vascular smooth muscle carbonic anhydrase I. We also studied in vitro and in vivo the effect of angiotensin II receptor blockers (irbesartan and candesartan) on purified carbonic anhydrase I and II, on vascular smooth muscle carbonic anhydrase I and on arterial blood pressure in humans and in animals. In vitro results showed that angiotensin II is a direct and stronger activator of carbonic anhydrase I than II. Angiotensin II receptor blockers reduced mainly carbonic anhydrase I activity and completely antagonized the activating effect of angiotensin II both on purified and on vascular smooth muscle carbonic anhydrase I. Our in vivo experiments showed that irbesartan and candesartan are powerful inhibitors of carbonic anhydrase I both in erythrocytes (in humans) and in vascular smooth muscles (in animals). In humans, irbesartan and candesartan progressively reduce arterial blood pressure in hypertensive subjects, in parallel with progressive reduction of erythrocyte carbonic anhydrase I activity. We believe that angiotensin II could have a dual mechanism of action: (1) angiotensin interacting with its receptor to form a stimulus-receptor complex; (2) the same stimulus directly acts on the carbonic anhydrase I isozyme (which might be coupled with angiotensin II receptors), ensuring an adequate pH for stimulus-receptor coupling for signal transmission into the cell and hence vasoconstriction.

Catecholamine-induced vasoconstriction is sensitive to carbonic anhydrase I activation

We studied the relationship between alpha- and beta-adrenergic agonists and the activity of carbonic anhydrase I and II in erythrocyte, clinical and vessel studies. Kinetic studies were performed. Adrenergic agonists increased erythrocyte carbonic anhydrase as follows: adrenaline by 75%, noradrenaline by 68%, isoprenaline by 55%, and orciprenaline by 62%. The kinetic data indicated a non-competitive mechanism of action. In clinical studies carbonic anhydrase I from erythrocytes increased by 87% after noradrenaline administration, by 71% after orciprenaline and by 82% after isoprenaline. The increase in carbonic anhydrase I paralleled the increase in blood pressure. Similar results were obtained in vessel studies on piglet vascular smooth muscle. We believe that adrenergic agonists may have a dual mechanism of action: the first one consists of a catecholamine action on its receptor with the formation of a stimulus-receptor complex. The second mechanism proposed completes the first one. By this second component of the mechanism, the same stimulus directly acts on the carbonic anhydrase I isozyme (that might be functionally coupled with adrenergic receptors), so that its activation ensures an adequate pH for stimulus-receptor coupling for signal transduction into the cell, resulting in vasoconstriction.

Membrane microviscosity, blood pressure and cytosolic pH in Dahl rats: the influence of plasma lipids

OBJECTIVE

To determine the relationships between blood pressure, membrane microviscosity, plasma lipids and cytosolic pH in Dahl rats susceptible or resistant to salt hypertension.

DESIGN AND METHODS

Blood pressure, plasma triglycerides and total cholesterol, platelet cytosolic pH (pHi) and the microviscosity of both outer membrane leaflet (TMA-DPH fluorescence anisotropy) and membrane lipid core (DPH fluorescence anisotropy) were studied in platelets and erythrocyte ghosts of Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats fed either a low-salt diet (0.3% NaCl) until the age of 9, 15 or 24 weeks or a high-salt diet (4% NaCl) for 5 or 10 weeks after weaning.

RESULTS

At low salt intake, DPH but not TMA-DPH anisotropy increased with age in platelets of SS/Jr rats. Chronic high salt intake was accompanied by an increase of DPH anisotropy in platelets but not in erythrocyte ghosts of SS/Jr rats. Platelet DPH anisotropy correlated positively with blood pressure of salt-loaded SS/Jr rats. Chronic high salt intake also reduced pHi in platelets, the regulation of which seemed to be related to the changes in TMA-DPH anisotropy. This especially concerns the thrombin-induced pHi rise which was inversely related to basal pHi, plasma lipids and TMA-DPH anisotropy. Altered membrane lipid composition might be the underlying mechanism because both membrane microviscosity and platelet pHi regulation were reported to correlate significantly with plasma triglycerides and/or cholesterol.

CONCLUSIONS

Platelets of salt hypertensive Dahl rats are characterized by an increased microviscosity of membrane lipid core which correlated positively with blood pressure. The major influence of plasma triglycerides on DPH anisotropy should be taken into consideration when investigating the links between membrane microviscosity and blood pressure. On the other hand, the changes in microviscosity of the outer membrane leaflet might be involved in pHi regulation (probably through control of the Na+/H+ exchanger).

Sodium sensitivity in young adults with high resting end-tidal CO2

BACKGROUND

Previous research with normotensive adults aged over 40 years ('older') found that sensitivity of blood pressure of subjects with high resting end-tidal partial pressures of CO2 to high sodium intake was greater than normal.

OBJECTIVE

To test the hypothesis that the lesser sensitivity of blood pressure of young normotensive adults to high sodium intake is also a function of resting end-tidal partial pressure of CO2.

DESIGN

Forty-eight Caucasian men and women (age 28.5 +/- 1.4 years) had a lower than normal dietary intake of sodium chloride for 4 days, and then ingested sodium chloride capsules for 7 days (an additional 190 mmol/day sodium chloride). Resting end-tidal partial pressure of CO2 and blood pressure, and 24 h ambulatory blood pressure, were measured before and after the high-sodium diet. Overnight urine samples were collected before and after the high-sodium diet to determine dietary compliance, and to assess changes in urinary excretion of endogenous digitalis-like factors (a ouabain-like factor, and a marinobufagenin-like factor) that covary with plasma volume.

RESULTS

Subjects with high end-tidal partial pressures of CO2 had lower resting heart rates and lower urinary excretion of ouabain-like factor before sodium loading. Sodium loading decreased mean partial pressure of CO2 (by 0.8 +/- 0.2 mmHg) and increased only ambulatory systolic blood pressure (by 2.1 +/- 0.8 mmHg) for the whole group. However, the changes in resting systolic (r = 0.32, P < 0.025) and diastolic (r = 0.36, P < 0.01) blood pressures and in 24 h systolic (r = 0.28, P < 0.05) blood pressure after sodium loading were all positive functions of individual resting end-tidal partial pressures of CO2. Sodium loading increased urinary excretion of marinobufagenin-like factor (by 1.78 +/- 0.88 nmol) and the magnitude of the individual increase was a function of end-tidal partial pressure of CO2.

CONCLUSIONS

The results indicate that a high resting partial pressure of CO2 augments the effects of high sodium intake on plasma volume, levels of endogenous digitalis-like factors, and blood pressure in young normotensive humans.

Cytosolic pH and calcium in Dahl salt-sensitive and salt-resistant rats: the relationship to plasma lipids

OBJECTIVE

To search for alterations of cytosolic pH and cell calcium handling in platelets and erythrocytes of Dahl rats susceptible and resistant to salt-induced hypertension.

DESIGN AND METHODS

Blood pressure, plasma lipids, platelet cytosolic calcium concentration ([Ca2+]i) and pH (pHi) together with thrombin-induced changes in these parameters as well as erythrocyte [Ca2+]i and 45Ca influx were determined in Dahl salt-sensitive (SS/Jr) and salt-resistant (SR/Jr) rats aged 9, 15 and 24 weeks, which were fed a low-salt diet (0.3% NaCl), and in animals fed high-salt diet (4% NaCl) for 5-10 weeks since weaning.

RESULTS

With a low salt intake platelet pHi was lower in SS/Jr than it was in SR/Jr rats, whereas basal platelet [Ca2+]i was similar in rats of both strains. The difference in basal pHi between SS/Jr and SR/Jr rats increased progressively with age of animals. A high salt intake from youth did not influence platelet [Ca2+]i in rats of either strain but it caused an earlier decrease in pHi in SR/Jr than it did in SS/Jr rats. Thrombin stimulation induced similar elevations of pHi and [Ca2+]i in rats of both strains, irrespective of age, salt intake and response of blood pressure to salt intake. Erythrocyte 45Ca influx and [Ca2+]i were greater for SS/Jr rats but only the latter parameter was correlated positively to blood pressure. Both regulation of platelet pHi and erythrocyte Ca2+ handling were significantly related to plasma lipid levels.

CONCLUSIONS

Platelets of SS/Jr rats fed a low-salt diet were characterized by a lower basal cytosolic pHi but unchanged [Ca2+]i relative to those of SR/Jr rats. Hypertension induced by high salt intake was associated with increased erythrocyte [Ca2+]i but not with elevation of platelet [Ca2+]i or alteration of response to stimulation with thrombin.

NHE-1 protein in vascular smooth muscle and lymphocytes from the spontaneously hypertensive rat

The present study examined the abundance of NHE-1 protein in cultured vascular smooth muscle cells (VSMCs), freshly isolated thymocytes, and fresh aortic tissue from spontaneously hypertensive rats (SHRs) and age-matched Wistar-Kyoto (WKY) rats. Two sets of affinity-purified antibodies (Ab[765-778] and Ab[698-711]) against different epitopes of the NHE-1 isoform of the Na+-H+ antiporter were used. Each set of antibodies recognized a major protein band at 105 to 110 kD that was more abundant in protein lysates prepared from cultured VSMCs from the SHR than those from WKY rats (Ab[765-778] 0.047 +/- 0.011 vs 0.010 +/- 0.002 O.D. units/10 microg protein, P<.001 for SHR and WKY, respectively; and Ab(698-711) 0.173 +/- 0.026 vs 0.087 +/- 0.028 O.D. units/10 microg protein, P<.05, for SHR and WKY, respectively). The increase in NHE-1 protein abundance in cultured VSMCs from the SHR was associated with a greater Vmax of the Na+-H+ antiporter as compared to those from WKY rats (17.93 +/- 2.07 vs 8.16 +/- 1.05 mmol H+/min, P<.001, respectively). In contrast to cultured VSMCs, there was no difference in the relative abundance of NHE-1 protein in fresh aortic tissue (0.075 +/- 0.018 vs 0.083 +/- 0.017 O.D. units/10 microg protein, from SHR and WKY, respectively) or in freshly isolated thymocytes (0.158 +/- 0.046 vs 0.226 +/- 0.054 O.D. units/10 microg protein, from SHR and WKY, respectively). We conclude that the increase in the Vmax of the Na+-H+ antiporter in cultured VSMCs from the SHR, compared to those from WKY rats, is due, at least in part, to increased levels of NHE-1 protein.

Erythrocyte sodium transport, intraplatelet pH, and calcium concentration in salt-sensitive hypertension

We evaluated changes in erythrocyte sodium transport systems, platelet pH, and calcium concentration induced by low and high salt intakes in a group of 50 essential hypertensive patients classified on the basis of their salt sensitivity. Patients received a standard diet with 20 mmol NaCl daily for 2 weeks supplemented in a single-blind fashion by placebo tablets the first 7 days and NaCl tablets the following 7 days. Salt sensitivity, defined as a significant rise (P <.05) in 24-hour mean blood pressure obtained by ambulatory blood pressure monitoring, was diagnosed in 22 (44%) patients. The remaining 28 (56%) were considered to have salt-resistant hypertension. In the entire group of hypertensive patients, high salt intake promoted a significant increase (P <.05) in the maximal rate of erythrocyte NA(+)-Li(+) countertransport (from 271 +/- 19 to 327 +/- 18 microM/(L cells/h) and of the Na(+)-dependent HCO3(-)-CL(-) exchanger (from 946 +/- 58 to 1237 +/- 92 microM/L cells/h) as well as in platelet pH (from 7.15+/-0 0.01 to 7.19+/-0.02 and calcium concentration (from 49+/-2 to 57 +/-2 nmol/L). Depending on salt sensitivity, high salt intake promoted opposing changes in some of the sodium transport systems studied. Salt-sensitive patients increased the maximal rate of the erythrocyte Na(+)-K(+) pump (fom 7.0 +/- 0.4 to 8.8 +/- 0.4 mmol/(L cells/h), Na(+)-K(+)-Cl(-) cotransport (from 416 +/- 37 to 612 +/- 41 micromol/(L cells/h), Na(+)-Li(+) countertransport (from 248 +/- 20 to 389 +/- 17 micromol/(L cells/h) at the end of the high salt period. Conversely, salt-resistant patients decreased the Na(+)-K(+) pump (from 8.0 +/- 0.4 to 6.9 +/- 0.3 mmol/(L cells/h) and Na(+)-K(+)-Cl(-) cotransport (from 578 +/- 53 to 481 +/- 43 micromol/(L cells/h). We conclude that modulation of erythrocyte sodium transport systems by high salt intake depends on salt sensitivity. The Na(+)-K(+) pump, Na(+)-K(+)-Cl(-) cotransport, and Na(+)-Li(+) countertransport increase in salt-sensitive patients, whereas the activity of these sodium transport systems tends to decrease in salt-resistant patients. Independent of salt sensitivity, high salt intake promotes a significant increase in the erythrocyte Na(+)-dependent HCO3(-)-Cl(-) exchanger, platelet pH, and calcium concentration in essential hypertensive patients.

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.

Regulation of intracellular pH in the spontaneously hypertensive rat. Role of bicarbonate-dependent transporters

Previous studies that have evaluated the Na(+)-H+ antiporter in cells from hypertensive subjects were generally performed under conditions in which HCO3-CO2, the physiological buffer system, was absent from the assay media. The objective of this study was to evaluate the activity of the Na(+)-H+ antiporter and that of the Na(+)-dependent and Na(+)-independent Cl(-)-HCO3- exchangers in cells assayed in the presence of HCO3-CO2 in the media. Lymphocytes from 6- to 8-week-old spontaneously hypertensive rats (SHR) and age-matched Wistar-Kyoto (WKY) rats were obtained from the thymus gland and assayed immediately after isolation. The activity of the Na(+)-H+ antiporter after stimulation by cell acidification (pHi approximately 6.4) was similar in SHR and WKY rats (18.67 +/- 1.03 and 16.12 +/- 0.92 mmol H+/L per minute, respectively). Recovery from cell alkalinization was effected by an Na(+)-independent Cl(-)-HCO3- exchanger, with maximal activity at an alkaline pHi (approximately 7.7). The stimulated activity of this Na(+)-independent Cl(-)-HCO3- exchanger was also not different between SHR and WKY cells (2.65 +/- 0.25 and 2.55 +/- 0.32 mmol H+/L per minute, respectively). Acute chloride removal produced a rise in pHi that was Na(+)-dependent and sensitive to 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS) but resistant to ethylisopropylamiloride (EIPA), reflecting the activity of an Na(+)-dependent Cl(-)-HCO3- exchanger. Unlike the Na(+)-H+ exchanger and the Na(+)-independent Cl(-)-HCO3- exchanger, which had their highest activities at extremes of pHi (low pHi, Na(+)-H+ exchanger, and high pHi, Na(+)-independent Cl(-)-HCO3- exchanger), the Na(+)-dependent Cl(-)-HCO3- exchanger had its maximal activity near steady-state pHi (approximately 7.1). No significant differences were found in the stimulated activity of this exchanger between cells from SHR and WKY rats (2.23 +/- 0.26 and 2.50 +/- 0.43 mmol H+/L per minute, respectively). The kinetic properties of the Na(+)-dependent and Na(+)-independent Cl(-)-HCO3- exchanger, examined as a function of external Cl-, were also virtually identical in cells from SHR and WKY rats. We conclude that in lymphocytes from SHR and WKY rats, the activity of the two Cl(-)-HCO3- exchangers, like that of the Na(+)-H+ exchanger, is dependent on the prevailing pHi. The Na(+)-dependent Cl(-)-HCO3- exchanger has its highest activity near steady-state pHi, suggesting an important role in the cell defense against intracellular acidosis under physiological conditions.(ABSTRACT TRUNCATED AT 400 WORDS)

Renal acid-base excretion in normotensive salt-sensitive humans

Reduced extracellular pH and bicarbonate levels recently have been reported in normotensive salt-sensitive subjects. To assess the possible role of altered renal acid-base handling in the perturbation of acid-base status in these individuals, we measured the renal acid-base excretion after an acute oral administration of either an alkali or acid load in normotensive salt-sensitive and salt-resistant men. Twenty-four young (22 to 29 years old), healthy male volunteers were placed on a low-salt diet (20 mmol NaCl per day) for 2 weeks with either 220 mmol NaCl or placebo added to the low-salt diet for 1 week each in a randomized single-blind crossover order. Salt sensitivity was defined as a significant drop in mean arterial pressure (> 3 mm Hg, mean of 60 readings taken on the seventh day of each diet, P < .05) during the low-salt diet. On the fifth and seventh days of each week, subjects were given an oral load of either sodium citrate (0.7 mmol/kg) or ammonium chloride (2.2 mmol/kg), respectively, in a randomized order, and arterial and urinary acid-base status was assessed at baseline and followed for 8 hours thereafter. According to the above definition, 13 subjects were considered salt sensitive. During the high-salt diet, mean arterial pressure was higher in the salt-sensitive than in the salt-resistant group (P < .01). Cumulative urinary bicarbonate excretion after the administration of sodium citrate was lower in the salt-sensitive than in the salt-resistant subjects during both the low-salt (46%, P < .001) and high-salt (32%, P < .01) diets.(ABSTRACT TRUNCATED AT 250 WORDS)