Renal functional reserve and microalbuminuria in offspring of hypertensive parents

Low Cortisone as a Novel Predictor of the Low-Renin Phenotype

A large proportion of patients with low-renin hypertension (LRH) correspond to primary aldosteronism (PA). However, some of these subjects have low to normal aldosterone. Since low renin is driven by excessive mineralocorticoids or glucocorticoids acting on mineralocorticoid receptors (MRs), we hypothesize that a low-cortisone condition, associated classically with 11βHSD2 deficiency, is a proxy of chronic MR activation by cortisol, which can also lead to low renin, elevated blood pressure, and renal and vascular alterations.

Objective

To evaluate low cortisone as a predictor of low renin activity and its association with parameters of kidney and vascular damage.

Methods

A cross-sectional study was carried out in 206 adult subjects. The subjects were classified according to low plasma renin activity (<1 ng/mL × hours) and low cortisone (<25th percentile).

Results

Plasma renin activity was associated with aldosterone (r = 0.36; P < .001) and cortisone (r = 0.22; P = .001). A binary logistic regression analysis showed that serum cortisone per ug/dL increase predicted the low-renin phenotype (OR 0.4, 95% CI 0.21-0.78). The receiver operating characteristic curves for cortisone showed an area under the curve of 0.6 to discriminate subjects with low renin activity from controls. The low-cortisone subjects showed higher albuminuria and PAI-1 and lower sodium excretion. The association study also showed that urinary cortisone was correlated with blood pressure and serum potassium (P < .05).

Conclusion

This is the first study showing that low cortisone is a predictor of a low-renin condition. Low cortisone also predicted surrogate markers of vascular and renal damage. Since the aldosterone to renin ratio is used in the screening of PA, low cortisone values should be considered additionally to avoid false positives in the aldosterone-renin ratio calculation.

Renal Functional Reserve Is Related to the Nondipping Phenotype and to the Exercise Heart Rate Response in Patients with Essential Hypertension and Preserved Renal Function

BACKGROUND

Renal functional reserve (RFR), defined as the difference between stress and resting glomerular filtration rate (GFR), may constitute a diagnostic tool to identify patients at higher risk of developing acute kidney injury or chronic kidney disease. Blunted RFR has been demonstrated in early stages of hypertension and has been attributed to impaired vascular reactivity due to an overactive sympathetic nervous system (SNS).

OBJECTIVE

The purpose of this study was to investigate whether RFR correlates with other phenotypes expressing overactivity of the SNS in patients with essential hypertension and preserved renal function.

METHODS

Thirty-six patients with untreated essential hypertension and a GFR >60 mL/min/1.73 m2 were enrolled. The following parameters were measured: RFR, 24-h ambulatory blood pressure (BP) profile, a treadmill stress test, and an echocardiographic examination. Urine and venous samples were obtained at specific time points for the determination of clinical parameters, and both resting and stress GFR were calculated by using endogenous creatinine clearance for the measurement of RFR after an acute oral protein load (1 g/kg).

RESULTS

Twenty-one patients had a RFR <30 mL/min/1.73 m2 and 15 had a RFR above this cutoff. A nondipping pattern of 24-h BP was significantly more frequent in patients with low RFR (57.1 vs. 25.0%, p < 0.05 for systolic BP and 52.3 vs. 10.0%, p < 0.02 for diastolic BP). Moreover, patients with lower RFR values showed a blunted heart rate (HR) response to exercise during treadmill test (r = 0.439, p < 0.05). None of the echocardiographic parameters differed between the two groups of patients.

CONCLUSIONS

In hypertensive patients with preserved GFR, reduced RFR is related to nondipping BP phenotype as well as to attenuated exercise HR response. Overactivity of the SNS may be a common pathway. Since loss of RFR may represent a risk factor for acute or chronic kidney injury, hypertensive patients with blunted RFR might need a more careful renal follow-up.

Haemodynamic or metabolic stimulation tests to reveal the renal functional response: requiem or revival?

Renal stimulation tests document the dynamic response of the glomerular filtration rate (GFR) after a single or a combination of stimuli, such as an intravenous infusion of dopamine or amino acids or an oral protein meal. The increment of the GFR above the unstimulated state has formerly been called the renal functional reserve (RFR). Although the concept of a renal reserve capacity has not withstood scientific scrutiny, the literature documenting renal stimulation merits renewed interest. An absent or a blunted response of the GFR after a stimulus indicates lost or diseased nephrons. This information is valuable in preventing, diagnosing and prognosticating acute kidney injury and pregnancy-related renal events as well as chronic kidney disease. However, before renal function testing is universally practiced, some shortcomings must be addressed. First, a common nomenclature should be decided upon. The expression of RFR should be replaced by renal functional response. Second, a simple protocol must be developed and propagated. Third, we suggest designing prospective studies linking a defective stimulatory response to emergence of renal injury biomarkers, to histological or morphological renal abnormalities and to adverse renal outcomes in different renal syndromes.

Association of parental hypertension with concentrations of select biomarkers in nonhypertensive offspring

Children of parents with hypertension are at increased risk of developing high blood pressure. We hypothesize that circulating concentrations of putative biomarkers (that may play a role in development of high blood pressure) are higher in nonhypertensive offspring of parents with hypertension. We compared concentrations of 4 different biomarkers (urinary albumin:creatinine ratio, circulating C-reactive protein, aldosterone:renin ratio, and plasminogen activator inhibitor-1) in nonhypertensive Framingham offspring study participants with none (n=233), 1 (n=474), or both (n=322) parents with hypertension. Parental hypertension was defined as onset before age 60 years, based on longitudinal observations of the original Framingham cohort. Serum C-reactive protein concentrations were higher in nonhypertensive offspring with 1 (median: 1.7; Q1 to Q3: 0.8 to 3.6 mg/L) or both parents with hypertension (median: 1.8; Q1 to Q3: 0.7 to 3.6 mg/L) compared with offspring without parental hypertension (median: 1.4; Q1 to Q3: 0.7 to 3.2 mg/L). In multivariable analyses, parental hypertension was associated with higher serum C-reactive protein concentration in offspring (15% increase per parent with hypertension; P=0.004). Prospectively, the relation of parental hypertension to longitudinal changes in blood pressure in the nonhypertensive offspring was attenuated on adjustment for C-reactive protein (P=0.04 for attenuation). The levels of the other biomarkers evaluated did not significantly differ in offspring according to parental hypertension status. In conclusion, serum C-reactive protein concentrations are higher in nonhypertensive offspring of parents with hypertension. These data suggest that inflammation may partly mediate the familial influences on hypertension risk.

Racial differences in microalbumin excretion in healthy adolescents

It has been suggested that "normal" levels of urine albumin excretion rate (AER) may be predictive of an increased risk for progression of hypertension, cardiovascular morbidity, and mortality. No data are available on the effect of race and gender on AER in normal youth. We evaluated AER in timed urine samples in subjects participating in a study of stress-induced pressure natriuresis. A total of 317 healthy, normotensive adolescents aged 15 to 18 years (155 males and 162 females; 216 blacks and 101 whites) participated in a 5-hour testing protocol, which included a 1-hour period of mental stress preceded and followed by a 2-hour rest period. AER (micrograms per minute) was determined after 60 minutes of rest, and log transformation was used to normalize the data. AER was significantly higher in blacks as compared with whites (P=0.006). We also found a race-by-sex interaction, which was driven by the low albumin excretion in white females (P=0.036). Indexing urine albumin to creatinine excretion revealed the same pattern. Among blacks, AER was also higher in subjects who demonstrated impaired stress-induced pressure natriuresis versus those with normal sodium excretion (P=0.024). AER was related to blood pressure only in African-American males. The relative elevation of AER in normotensive black adolescents and the association with impaired pressure natriuresis and blood pressure is noteworthy. These findings suggest that albumin excretion may be a marker for a population at increased risk for the development of vascular and renal injury even before the manifestation of hypertension.

Uric acid excretion and dopamine-induced glomerular filtration response in patients with IgA glomerulonephritis

BACKGROUND/AIM

It is unknown to what extent uric acid (UA) may affect vessel function and participate in tubulointerstitial damage. We examined the relationship between intrarenal vessel function and serum UA and its excretion in association with urinary N-acetyl-beta-D-glucosaminidase (NAG).

METHODS

In 50 IgA patients (mean age 34.7 +/- 9.3 years) and 15 controls (mean age 33.5 +/- 6.9 years) with a creatinine clearance of 99.4 +/- 21.6 and 118.1 +/- 17.2 ml/min, respectively, the renal vascular function was estimated based on the dopamine-induced glomerular filtration response (DIR; see text). The DIR was measured using two 120-min creatinine clearance values (before and after intravenous administration of 2 g/kg/min dopamine). Serum UA, triglycerides and cholesterol and urinary NAG (24 h) and protein and UA excretion were measured.

RESULTS

Patients with IgA nephropathy versus controls: DIR 8.80 +/- 6.6 vs. 12.83% (p < 0.01), NAG 7.25 +/- 3.30 vs. 4.69 +/- 1.12 U/g creatinine (p < 0.01), and fractional UA excretion 7.80 +/- 2.20 versus 6.29 +/- 1.80% (p < 0.01). A negative correlation between DIR and NAG was found; regression analysis showed a more prominent relationship in the patients (NAG = 9.99 - 0.29x DIR) than in the controls (NAG = 5.50 - 0.06x DIR). UA and urate excretion and NAG in the patients correlated with DIR (r = -0.39, p < 0.02; r = -0.29, p < 0.04, and r = 0.59, p < 0.001, respectively). Multivariate analysis showed an association of DIR (R(2) = 0.39) with NAG but not with proteinuria and UA and UA excretion; the NAG excretion (R(2) = 0.56) correlated significantly with UA and DIR.

CONCLUSION

It is suggested that UA plays a role, associated with tubular dysfunction, in the regulation of intrarenal vessel function.

Low-grade albuminuria and the risks of hypertension and blood pressure progression

BACKGROUND

It has been postulated that glomerular hyperfiltration and endothelial dysfunction are early features of essential hypertension that may antedate blood pressure elevation. Microalbuminuria, a marker of glomerular hyperfiltration and endothelial dysfunction, has been described in individuals with established hypertension, but its role as a biomarker of preclinical stages of this disease has not been investigated prospectively.

METHODS AND RESULTS

We examined the association between urinary albumin excretion and the risks of hypertension and blood pressure progression in 1499 nonhypertensive individuals (58% women) without diabetes. During a mean follow-up of 2.9 years, 230 participants (15%) developed hypertension and 499 (33%) progressed to a higher blood pressure category (defined by the sixth report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure). In multivariable logistic regressions that adjusted for known risk factors, the urine albumin-creatinine ratio (UACR) was a significant predictor of incident hypertension (adjusted OR 1.20, 95% CI 1.01 to 1.44, per 1-SD increment in log UACR). Compared with those in the lowest UACR quartile, participants in the highest quartile (men: >6.66 mg/g; women: >15.24 mg/g) had an approximately 2-fold risk of developing hypertension (adjusted OR 1.93, P=0.006) and 1.5-fold risk of blood pressure progression (adjusted OR 1.45, P=0.03).

CONCLUSIONS

Urinary albumin excretion predicts blood pressure progression in nondiabetic, nonhypertensive individuals incrementally over established risk factors and at levels well below the conventional threshold for microalbuminuria. UACR may be a useful biomarker for identifying individuals most likely to develop hypertension.

Effect of 12-month therapy with omega-3 polyunsaturated acids on glomerular filtration response to dopamine in IgA nephropathy

BACKGROUND

Omega-3 polyunsaturated acids therapy is efficient in primary IgA nephropathy. It is unknown whether doses of omega-3 smaller than those given previously are still effective. The aim of the study was to examine the effect of omega-3 therapy on renal vascular function in relation to proteinuria and urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG).

METHODS

20 IgA patients aged 36.5 +/- 10.77 with creatinine clearance (Cr(cl)) 105.71 +/- 27.3 ml/min and proteinuria 3.31 +/- 2.01 g/24 h were given orally 810 mg EPA and 540 mg DHA daily for 12 months. Before and at the end of the study, 24-hour proteinuria, serum homocysteine, and Cr(cl) were measured. At the same time, renal vascular function was estimated as dopamine-induced glomerular filtration response (DIR). DIR was measured as: two 120-min lasting Cr(cl) (before and during 2 microg/kg b.w./min i.v. dopamine).

RESULTS

The results obtained during follow-up were as follows (baseline vs. after therapy): DIR 14.9 +/- 16.4 vs. 30.3 +/- 14.3% (p < 0.01); urine protein 2.31 +/- 2.01 vs. 1.31 +/- 1.37 g/24 h (p < 0.01); (Cr(cl)) 105.71 +/- 27.3 vs. 103.9 +/- 20.9 ml/min (n.s.); NAG 8.3 +/- 1.8 vs. 6.0 +/- 1.2 U/g(creat) (p < 0.01), and homocysteine 16.2 +/- 3.15 vs. 13.8 +/- 2.6 micromol/l (p < 0.05). The only correlation found was linear correlation between basal DIR and DIR change (r = -0.570; p < 0.010) and basal NAG (r = -0.460; p < 0.50).

CONCLUSIONS

Omega-3 supplementation is associated with the improvement of both renal vascular function and tubule function.

[Evaluation of two rapid tests for the determination of microalbuminuria and the urinary albumin/creatinine ratio]

OBJECTIVE

Microalbuminuria screening is justified on the grounds of its cost-benefit ratio in patients at risk of kidney damage while the process is still reversible. The aim of the present study was to evaluate the DCA 2000 analyser and the Clinitek 50 system (Bayer), which simultaneously measure urinary albumin and creatinine levels to adopt them as rapid methods for microalbuminuria detection.

METHODS

One hundred twenty-seven urine samples from pediatric patients with various disorders were assessed. Albumin, creatinine, and the albumin/creatinine ratio were determined using the DCA 2000 analyzer and the Clinitek 50 system, which were compared against the usual reference laboratory methods.

RESULTS

The correlation coefficient of nephelometric values vs the DCA 2000 analyzer was 0.914 for albumin, 0.970 for creatinine and 0.839 for the albumin/creatinine ratio. At an albumin cut-off concentration of 30 mg/l, the sensitivity, specificity, positive predictive value and negative predictive value were 100 %, 93 %, 84 % and 100 % for the DCA 2000 analyzer and 91.7 %, 86 %, 55 % and 98 % for the Clinitek 50 system. ROC curve analysis showed that the DCA 2000 system was more effective than the Clinitek 50 in microalbuminuria screening.

CONCLUSIONS

The data obtained with the DCA 2000 system showed close agreement with those obtained with reference laboratory methods. The immediate availability of results is a great advantage in clinical practice. The Clinitek-Microalbumin dipstick system is a semiquantitative method that is easy to use, low in cost, simple and useful for screening, but it is less reliable as a follow-up method.

Diagnosis and treatment of hypertension in children and adolescents

PURPOSE

To provide nurse practitioners (NPs) with updated information regarding the etiology, diagnosis, and treatment of childhood hypertension.

DATA SOURCES

Extensive review of the scientific literature regarding hypertension, including the latest NIH recommendations.

CONCLUSIONS

Hypertension affects more than 350,000 American children. While the majority of hypertension in early childhood occurs from secondary causes, the incidence of essential hypertension in later childhood and adolescence is rising, raising concerns as elevated pressures in childhood "track" into adulthood. Early detection and treatment of elevated childhood pressures represent important steps in reducing long-term cardiovascular risk.

IMPLICATIONS FOR PRACTICE

NPs must be able to accurately differentiate between primary and secondary hypertension in childhood. Secondary hypertension requires prompt diagnosis and treatment, and controlling primary childhood hypertension has lifelong implications. Given the familial predisposition to hypertension, it is important for adult NPs to be aware of the risks faced by children of hypertensive patients.

Excessive urinary albumin levels are associated with future cardiovascular mortality in postmenopausal women

BACKGROUND

Microalbuminuria is an early predictor of cardiovascular morbidity and mortality, in both diabetic patients and hypertensive patients. Little is known about the relation of microalbuminuria to cardiovascular disease in women of the general population.

METHODS AND RESULTS

We have studied the relation of urinary albumin levels to cardiovascular mortality in a cohort study of 12 239 postmenopausal women living in Utrecht, the Netherlands. The initial age was between 52 and 67 years. Women were followed on vital status between 1976 and 1995 (168 513 women-years). Albumin was determined in the urine of 561 cases and 557 controls. Data were analyzed by using a nested case-control design. The cardiovascular mortality rate (95% CI) for women who were in the highest quintile of urinary albumin levels was 13.2/1000 years (8.1 to 20.9) compared with 2.6/1000 years (2.3 to 3.1) in women without detectable urinary albumin. The age-adjusted rate ratio (95% CI) between these groups was 4.4 (2.6 to 7.6).

CONCLUSIONS

This is the first large cohort study that confirms a predictive role of urinary albumin for the risk of future cardiovascular mortality independent of hypertension and diabetes. Our findings support the hypothesis that microalbuminuria is a reflection of vascular damage and a marker of early arterial disease in women from the general population.

Early alteration in glomerular reserve in humans at genetic risk of essential hypertension: mechanisms and consequences

Essential hypertension has a familial predisposition, but the phenotype of elevated blood pressure has delayed penetrance. Because the kidney is a crucial determinant of blood pressure homeostasis, we studied early glomerular alterations in still-normotensive young subjects at genetic risk of hypertension. Thirty-nine normotensive adults (mean age 29 to 31 years), stratified by genetic risk (parental family history [FH]) of hypertension (26 with positive FH [FH+], 13 with negative FH [FH-]), underwent intravenous infusion of mixed amino acids. Before and during amino acid administration, we measured glomerular filtration rate (GFR), putative second messengers of amino acids (nitric oxide [NO.] metabolites and cGMP), serum insulin and amino acid concentrations, and the FE(Li)+ as an index of renal proximal tubular reabsorption. The FH+ group had a blunted GFR rise in response to amino acids (2.43+/-8.16% versus 31.0+/-13.4% rise, P:=0.0126). The amino acid-induced change in GFR correlated (r=0.786, P:<0.01) with the change in urinary NO. metabolite excretion; a diminished rise in urinary NO. metabolite excretion in the FH+ group (P:=0.0105) suggested a biochemical mechanism for the different GFR responses between FH groups: a relative inability to convert arginine to NO. The FH+ group had a far lower initial cGMP excretion at baseline (261+/-21.1 versus 579+/-84.9 nmol. h(-1)/1.73 m(2), P:=0.001), although cGMP did not change during the amino acid infusion (P:=0.703). FH status, baseline GFR, and baseline serum insulin jointly predicted GFR response to amino acids (P:=0.0013), accounting for approximately 45% of the variance in GFR response. Decline in FE(Li)+, an inverse index of proximal tubular reabsorption, paralleled increase in GFR (r=-0.506, P:=0.01), suggesting differences in proximal tubular reabsorption during amino acids between the FH groups. GFR response to amino acid infusion was blunted in the FH+ group despite significantly higher serum concentrations of 6 amino acids (arginine, isoleucine, leucine, methionine, phenylalanine, and valine) in the FH+ group, suggesting a novel form of insulin resistance (to the amino acid-translocating action of insulin) in FH+ subjects. We conclude that blunted glomerular filtration reserve in response to amino acids is an early-penetrance phenotype seen even in still-normotensive subjects at genetic risk of hypertension and is linked to impaired formation of NO. in the kidney. Corresponding changes in GFR and fractional excretion of Li(+) suggest that altered proximal tubular reabsorption after amino acids is an early pathophysiologic mechanism. Resistance to the amino acid-translocating actions of insulin may play a role in the biological response to amino acids in this setting. This glomerular reserve phenotype may be useful in genetic studies of renal traits preceding or predisposing to hypertension.

Glomerular hyperfiltration, high renin, and low- extracellular volume in high blood pressure

Abnormal renovascular resistance and glomerular filtration rate are characteristic of established hypertension and may also be involved in its pathogenesis. To determine renal and body fluid correlates of the predisposition to high blood pressure, we examined 100 healthy young adults with high or low blood pressure. Within each group, half had parents with high blood pressures, and half had parents with low blood pressures. Renal function and hemodynamics, body fluid volumes, and relevant hormones and genotypes were measured. Subjects with high personal and parental blood pressures had the highest levels of glomerular filtration rate (P<0.02) and plasma active renin concentration and low levels of exchangeable sodium and plasma volume (P<0.02). High glomerular filtration rate was not associated with differences in urinary kallikrein or prostaglandins. Polymorphisms of the renin, angiotensin-converting enzyme, and angiotensinogen genes were not associated with differences in glomerular filtration rate or renin. Subjects with high personal, but low parental, blood pressures had low exchangeable sodium and plasma volumes (P<0.02) but normal glomerular filtration rates. In this population, extracellular volume depletion and high renin are correlates of high blood pressure in early adulthood, and glomerular hyperfiltration is a feature of those who also have familial predisposition to high blood pressure.

Microalbuminuria in essential hypertension: significance, pathophysiology, and therapeutic implications

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). The significance of this association, which is the object of this review, is not well established. Hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night, and higher serum levels of cholesterol, triglycerides, and uric acid than patients with normal UAE. Levels of high-density lipoprotein cholesterol, on the other hand, were lower in patients with microalbuminuria than in those with normal UAE. Patients with microalbuminuria manifested greater incidence of insulin resistance and thicker carotid arteries than patients with normal UAE. After a follow-up of 7 years, we observed that 12 cardiovascular events occurred among 54 (21.3%) patients with microalbuminuria and only two such events among 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE, cholesterol level, and diastolic blood pressure were independent predictors of the cardiovascular outcome. Rate of creatinine clearance from patients with microalbuminuria decreased more than that from those with normal UAE. In conclusion, these studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which results in hypertensive patients having a greater incidence of cardiovascular events and a greater decline in renal function than patients with normal UAE.

Induction of microalbuminuria by l-arginine infusion in healthy individuals: an insight into the mechanisms of proteinuria

Despite evidence from individuals with diabetes mellitus or reduced renal mass, the actual relationship between protein- or amino acid-induced changes in renal function and urinary albumin excretion (UAE) is largely unknown in subjects without renal disease. In humans, infusions of l-arginine have been used recently in vascular and renal pathophysiological studies. The present study was undertaken to analyze the mechanisms involved in a particular effect; namely, the behavior of UAE during amino acid loading. A prospective interventional protocol was performed on 10 healthy adults by means of an intravenous infusion of l-arginine. The main results show that l-arginine induced a significant increase in UAE from 13.1 +/- 3.8 before to 53.3 +/- 11.1 microgram/min after the infusion (P < 0.005). This increment was simultaneous to an increase in glomerular filtration rate (GFR) and renal plasma flow (RPF). Furthermore, l-arginine markedly increased the urinary excretion of beta2-microglobulin. UAE correlated significantly with GFR (r = 0. 738; P = 0.014) and RPF (r = 0.942; P < 0.0001), but not with urinary beta2-microglobulin (r = 0.05; P = not significant). Furthermore, marked differences (P = 0.001) were found between the percentage of increase in UAE (306.8% +/- 163.2%) with respect to either albumin filtered load (FLAlb; 57.9% +/- 16.3%) and beta2-microglobulin excretion (1,088.5% +/- 424.6%). No changes were found in vehicle-infused individuals. In conclusion, the present study shows, in controlled conditions, that l-arginine infusion induces a relevant increase in UAE in healthy individuals that significantly exceeds that expected from the increase in GFR alone. The intense and simultaneous increment in beta2-microglobulin excretion strongly suggests that the effect of l-arginine on UAE is, in a relevant part, mediated through a blockade in the tubular protein reabsorption pathways. However, the profound differences observed in the changes induced by l-arginine on UAE and beta2-microglobulin excretion and the differences in the correlation of UAE and beta2-microglobulin with respect to GFR suggest that substantial diversity exists in the mechanisms by which l-arginine affects the renal management of albumin and beta2-microglobulin. These findings are relevant for understanding the renal response to l-arginine and protein/amino acid loads.

Renal functional reserve in insulin dependent diabetic children

BACKGROUND

Microalbuminuria has been shown to be predictive for clinical diabetic nephropathy. Renal functional reserve (RFR), as a response to protein loading in a short period of time, is a parameter to assess the ability of kidneys to increase the glomerular filtration rate (GFR). The aim of this study was to predict the early phase of diabetic nephropathy by measuring urinary albumin level and RFR capacity in patients with insulin-dependent diabetes mellitus (IDDM).

METHODS

Twenty-two patients with IDDM were studied: 11 with a disease duration of less than 5 years (group 1) and 11 with a disease duration of more than 5 years (group 2). As the control group, 15 healthy children (group 3) were included in the study. At the beginning of the study, glucose was measured and the urinary albumin/creatinine ratio was calculated. Average glycosylated hemoglobin (HbA1c) over 1 year was determined. After protein loading (red meat containing 2 g/kg of protein), the creatinine clearance was calculated at each hour for a duration of 4 h. The RFR was accepted as the peak percentage increase in GFR over the baseline value.

RESULTS

Although metabolic control in group 2 was better, the RFR in group 2 was significantly lower than in group 1 (P < 0.05). Urinary microalbumin levels between the groups did not differ (P > 0.05). In two patients in whom microalbuminuria was detected, the RFR was much lower.

CONCLUSIONS

Detecting lower RFR levels in patients with normal urinary albumin excretion, as well as in patients with microalbuminuria, may support the idea that the RFR capacity is more sensitive than microalbuminuria in assessing the early phase of diabetic nephropathy.

Nephropathy of type II diabetes: evidence for hereditary factors?

Family studies point to an important genetic element in the genesis of diabetic nephropathy, but it is not known whether renal abnormalities are present prior to the onset of diabetes. To address this issue we examined all consecutive patients suffering from type II diabetes with a duration of more than 10 years who attended a diabetes outpatient clinic. Ninety-four patients had nephropathy, 307 did not. All offspring who were phenotypically normal (no hypertension, normal oral glucose tolerance, non-smoking) and agreed to participate were examined, 26 from nephropathic and 30 from non-nephropathic diabetic parents. They were compared with 30 offspring matched for age, gender and BMI from non-diabetic parents as controls. We measured urinary albumin excretion under baseline conditions and at several time points after ingestion of 300 g cooked beef and submaximal treadmill exercise, respectively. In addition, casual blood pressure, ambulatory blood pressure, urinary albumin and urinary alpha-1-microglobulin were measured. Primary renal disease was excluded by clinical examination. Under baseline conditions, median urinary albumin excretion rate (AER; microgram/min) was significantly (P < 0.005) higher in offspring of nephropathic type II diabetic patients (7.8; range 1.04 to 19.5) than in the offspring of non-nephropathic type II diabetic patients (4.8; 0.36 to 17.5) and controls (4.4; 0.16 to 18.4). Submaximal treadmill exercise caused a greater proportional increase of AER in offspring of nephropathic type II diabetics (median 16-fold) than in offspring of non-nephropathic diabetic patients (6.3-fold) or controls (4.8-fold). In offspring of nephropathic diabetic patients casual and particularly ambulatory systolic blood pressures were significantly higher, but AER was not correlated with blood pressure. In summary, higher values, albeit within the normal range, for baseline and postexercise albuminuria were noted in phenotypically normal offspring of parents with type II diabetes and nephropathy. The observation suggests that changes in transglomerular albumin traffic are demonstrable prior to the onset of diabetes and diabetic nephropathy in subjects with a potential genetic predisposition to these conditions.

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 or absence of renal function reserve, in response to a chronic protein load, is thought to be useful in predicting the existence of glomerular hypertension. Intrarenal hemodynamic parameters in the sodium-sensitive type of essential hypertension were therefore calculated by analyzing the pressure-natriuresis curve, and the preservation of renal function reserve was evaluated. Fifteen patients with essential hypertension 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 restriction were considered sodium sensitive (n = 7), with the remaining patients classified as non-sodium sensitive (n = 8). There were no significant differences in mean arterial pressure (125 +/- 2 mm Hg), glomerular 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 elevated in sodium-sensitive patients relative to that in non-sodium-sensitive patients, whereas the whole kidney ultrafiltration coefficient of glomerular 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 loading increased both glomerular filtration and renal plasma flow rates in study 2. Although the sodium sensitivity of blood pressure showed no significant correlation with the increase in either glomerular filtration or renal plasma flow rate, it showed a weak negative correlation with the increase in filtration fraction (r = -0.69, p < 0.06), which is the ratio of the two rates. Taken together, these results suggest that glomerular capillary pressure is elevated and renal function reserve is impaired in patients with sodium-sensitive essential hypertension.

Dyslipoproteinemia and other risk factors for atherosclerosis in children and adolescents

The early lesions of atherosclerosis in youth are strongly related to antemortem levels of total and low density lipoprotein (LDL) cholesterol, very low density lipoprotein (VLDL) cholesterol, and triglyceride, to ponderal index and to systolic and diastolic blood pressure. The major apolipoproteins of LDL and high density lipoprotein (HDL), apo B and apo A1, respectively, as well as levels of Lp(a) lipoprotein are often abnormal in children born to a parent with coronary artery disease (CAD). Other risk factors for CAD include obesity, high blood pressure, cigarette smoking, diabetes mellitus, positive family history of CAD and physical inactivity. Children from families with premature CAD, familial dyslipidemia or hypertension, and/or two other risk factors should have a lipoprotein profile determined. The first form of treatment is a diet low in total fat, saturated fat and cholesterol, combined with treatment of overnutrition and obesity, if necessary, and regular habits of aerobic physical activity. Children with inherited disorders of LDL metabolism may require the addition of lipid lowering therapy. The early detection and treatment of youth at risk for premature CAD offers the greatest promise to decrease morbidity and mortality.

Microalbuminuria: pathogenesis, prognosis and management

The development in recent years of sensitive assays specific for albumin has facilitated extensive investigation of the pathophysiology and clinical significance of microalbuminuria. It is now clear that the appearance of microalbuminuria represents a crucial event in the natural histories of diabetes mellitus and essential hypertension. It reflects the presence of generalized vascular damage and is strongly predictive of subsequent renal failure, cardiovascular morbidity, and death. Therapeutic interventions, including strict diabetic and blood-pressure control, can reduce microalbuminuria and improve the overall prognosis. The detection and treatment of microalbuminuria in these high-risk groups should now form an integral part of their management. Large-scale screening programmes are also recommended for insulin-dependent diabetics.

Albuminuria in normals and essential hypertension

The prevalence and determinants of urinary albumin excretion rate (AER) were assessed in lean and overweight normotensive subjects (NT) and patients with essential hypertension (EH). In NT and EH, the presence of overweight was associated with a significant exacerbation of AER. In the normotensive population, AER was higher in subjects with a positive family history of hypertension. An important role for smoking was observed in the hypertensive population; in fact, the prevalence of microalbuminuria (MA) was almost twofold in lean hypertensive smokers when compared to nonsmokers. Among other determinants of AER, a major influence of systolic arterial pressure, urinary excretion of urea (an estimate of protein intake), and high-density lipoprotein (HDL) cholesterol (inversely correlated with AER) was observed mainly in lean EH patients. The significance of microalbuminuria is unclear. Is it a marker of cardiovascular risk and/or a predictor of the future development of renal disease in EH?

Elevated serum insulin levels in patients with essential hypertension and microalbuminuria

Hyperinsulinemia, insulin resistance, or both have been described in patients with essential hypertension. Previous work from our laboratory has shown that in hypertensive patients with microalbuminuria, dyslipidemia and abnormal patterns in the diurnal variations of blood pressure are frequently associated. Whether hyperinsulinemia and microalbuminuria are directly related has not been determined. To test this possibility, we measured the plasma insulin response to an oral glucose load in 25 patients with or without microalbuminuria and 20 normotensive control subjects. Serum lipid profile and 24-hour ambulatory blood pressure were obtained. In the hypertensive patients as a group, the plasma insulin response to glucose (evaluated as the insulin area under the curve) was significantly enhanced compared with a group of 20 normotensive healthy control subjects (46,311 +/- 3745 and 27,557 +/- 2563 pmol/L x 2 hours, P < .01). When the hypertensive patients were subdivided according to their albumin excretion rate, the microalbuminuric patients had significantly higher plasma glucose (969 +/- 45.2 versus 762 +/- 28.7 mmol/L x 2 hours, P < .01) and insulin (59,172 +/- 5964 versus 37,737 +/- 3422 pmol/L x 2 hours, P < .01) area under the curve values. In addition, a significant direct correlation was found to exist between insulin area under the curve and the urinary albumin excretion rate (r = .63, P < .001). Serum levels of lipoprotein(a) were significantly greater (P < .01) in patients with than in those without microalbuminuria and in control subjects. Furthermore, daytime diastolic blood pressure and nighttime systolic and diastolic blood pressure values were greater in patients with than in those without microalbuminuria.(ABSTRACT TRUNCATED AT 250 WORDS)

Microalbuminuria in salt-sensitive patients. A marker for renal and cardiovascular risk factors

We previously showed that a high salt diet increases glomerular capillary pressure in salt-sensitive hypertensive patients and suggested that this may underlie the greater propensity of these patients to develop renal failure. Because microalbuminuria is considered an initial sign of renal damage, we have tested whether salt-sensitive patients display greater urinary albumin excretion than salt-resistant hypertensive patients. Twenty-two patients were placed on a low sodium intake (20 mEq/d) for 7 days followed by a high sodium diet (250 mEq/d) for 7 more days. Twelve patients were classified as salt sensitive and 10 as salt resistant. Urinary albumin excretion was greater in salt-sensitive than salt-resistant patients (54 +/- 11 versus 22 +/- 5 mg/24 h, P < .01). During the low sodium diet, glomerular filtration rate, renal plasma flow, and filtration fraction were similar between the two groups. During the high sodium intake, glomerular filtration, renal plasma flow, filtration fraction, and calculated intraglomerular pressure did not change in salt-resistant patients; in salt-sensitive patients, however, renal plasma flow decreased, and filtration fraction and intraglomerular pressure increased, whereas glomerular filtration rate did not change. Urinary albumin excretion was significantly correlated with glomerular capillary pressure. Salt-sensitive patients displayed higher serum levels of low-density lipoprotein cholesterol and lipoprotein(a) and lower levels of high-density lipoprotein cholesterol than salt-resistant patients. These studies have shown greater urinary albumin excretion and serum concentrations of atherogenic lipoproteins in salt-sensitive than in salt-resistant hypertensive patients, suggesting that salt sensitivity may be a marker for greater risk of renal and cardiovascular complications.

Hypertensive end-stage renal disease in blacks: the role of end-stage renal disease surveillance

The end-stage renal disease (ESRD) networks and the United States Renal Data System recently have described the epidemiology of ESRD and broadened our appreciation of the impact of ESRD in the United States. This surveillance system also can be used to study the occurrence and control of ESRD. Among the epidemiologic study designs available to conduct research on the etiology of renal failure, case-control studies are uniquely suited for this purpose. The case of hypertensive ESRD illustrates this concept; risk factors for hypertensive ESRD, as a hypothetical exposure in case-control studies, are briefly described. Case-control studies are an efficient and readily used means to study causes of renal failure.

The relationship of arterial compliance with endothelial-derived proteins of the hemostatic system

Cardiovascular risk factors associated with hypertension include alterations in arterial compliance and an increased tendency to thrombosis. In this study we examined the relationship between arterial compliance and endothelial derived components of the hemostatic system: von Willebrand factor (vWF) and tissue plasminogen activator (t-PA). Ten males (4 normal and 6 untreated hypertensives, 41 +/- 12 years) were studied. Compliance of proximal (large vessel) and distal (small vessel) arteries was measured by intraarterial pulse wave analysis; left ventricular wall thickness by echocardiography; and vWF and t-PA by immunoassay of plasma obtained before and immediately after maximum treadmill exercise. Baseline t-PA and vWF correlated inversely with distal compliance (r = -0.74, p = 0.01; r = -0.56, p = 0.09). Exercise strengthened the relationship between vWF and both distal compliance (r = -0.56 to r = -0.86) and proximal compliance (r = -0.44 to r = -0.70). Moreover, post-exercise levels of vWF and t-PA were each significantly related to left ventricular posterior wall and septal thickness. Of note, these protein concentrations correlated more strongly with arterial compliance and left ventricular wall thickness than with blood pressure. Thus, arterial compliance and left ventricular wall thickness appear to be more powerful than blood pressure as predictors of the endothelial release of vWF and t-PA in response to exercise. These findings indicate that some of the key cardiac and arterial characteristics of hypertension might be linked to increased endothelial reactivity to hemodynamic stress.

Heredity and hypertension: impact on metabolic characteristics

This study was performed to evaluate the possible role of heredity in the clinical characteristics of hypertension. Metabolic, endocrine, and renal measurements were compared in subjects with normal blood pressure who had a family history of hypertension (n = 60) with those of subjects with normal blood pressure who did not have a family history of hypertension (n = 48). The groups were matched for age (mean, 44 +/- 2 years and 45 +/- 2 years) and blood pressure (127 +/- 1/77 +/- 1 mm Hg and 127 +/- 2/77 +/- 1 mm Hg). The following parameters were higher in the patients with a family history of hypertension than in those without. Plasma insulin concentrations (14.1 +/- 1.1 vs 10.8 +/- 1.0 microU/ml; p less than 0.05), insulin-glucose ratio (0.15 +/- 0.01 vs 0.11 +/- 0.010; p less than 0.05), norepinephrine concentrations (315 +/- 24 pg/ml vs 208 +/- 20 pg/ml; p less than 0.01), plasma renin activity (2.1 +/- 0.2 ng Angl/ml/hr vs 1.6 +/- 0.2 ng Angl/ml/hr; p less than 0.02), total cholesterol levels (217 +/- 8 mg/dl vs 197 +/- 0.3 mg/dl; p less than 0.05), creatinine clearance (125 +/- 9 ml/min vs 96 +/- 8 ml/min; p less than 0.01), and albumin excretion rate (3.2 +/- 0.3 micrograms/min vs 2.6 +/- 0.3 micrograms/min; p = 0.1). Moreover, patients with a family history of hypertension had smaller increases in systolic blood pressure during treadmill exercise (55 +/- 3 mm Hg vs 64 +/- 3 mm Hg; p less than 0.03). There were no differences in echocardiographic left ventricular mass index between the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular and metabolic characteristics of hypertension

Hypertension is now seen as a broader condition than high blood pressure alone. Large-scale epidemiologic studies have established that high blood pressure is associated with an increased risk of cardiovascular events, but clinical trials of antihypertensive therapy have shown an inconsistent reduction in major cardiovascular endpoints. Importantly, the incidence of coronary disease has been reduced to only a small extent, suggesting that factors beyond high blood pressure are important in the genesis of atherosclerotic disease in hypertensive patients. It is evident, for example, that patients with hypertension have an exaggerated vulnerability to the consequences of lipid abnormalities. Moreover, it has recently been established that hypertension is characterized by insulin resistance and altered glucose tolerance. As a result, high plasma concentrations of insulin produce proliferative effects on vascular smooth muscle and connective tissue, and they may adversely affect the lipid profile. The left ventricle is also involved in hypertension--independent of blood pressure. There is growing evidence that there are increases in the muscle mass of the left ventricle and changes in its diastolic filling characteristics at the very early stages of hypertension. The arterial circulation is similarly involved, for alterations in structure or function, reflected by diminished arterial compliance, can be demonstrated prior to the appearance of clinical hypertension. Treatment designed to protect hypertensive patients from cardiovascular events must not only be based on blood pressure, but must take into account all the components of the hypertension syndrome.

Pathogenesis of the essential hypertensions

The pathogenesis of essential hypertension (EH) is reviewed with a special focus on the development phase or the pre-hypertensive period. Three animal models are presented: the spontaneously hypertensive rat, the Dahl's salt-sensitive rat, and the Milan hypertensive rat. Some of the findings in animal models have inspired new fields and technical approaches for studying EH in man. From the original idea of Page, a new mosaic of various etiological parameters serves as a basis for reviewing the multiple facets of EH in man. One must conclude that EH is heterogeneous disease and most likely every single hypertensive patient belongs to a subgroup of the whole population of hypertensives.