Blood pressure and renal function

Associations of smoking with alterations in renal hemodynamics may depend on sex--investigations in potential kidney donors

BACKGROUND/AIMS

Cigarette smoking is a risk factor for renal damage, but little is known about subclinical effects of smoking on renal hemodynamics and parameters of renal function in humans. We examined the associations of smoking with systemic and renal hemodynamics and renal function parameters in healthy individuals.

METHODS

Data from 196 potential living kidney donors were analysed retrospectively. Mean arterial blood pressure (MAP), effective renal plasma flow (ERPF) and creatinine clearance had been measured. We additionally calculated parameters of renal hemodynamics. Data were analyzed for the effects of smoking and sex dependent on age and MAP.

RESULTS

Systemic and renal hemodynamic parameters did not differ between smokers and non-smokers. In non-smokers of both sexes MAP was negatively correlated with ERPF, and higher MAP was associated with increased renal vascular resistance and with afferent arteriolar resistance, with glomerular pressure (PG) remaining constant. However, in male, but not in female smokers, ERPF and PG increased with MAP. A correlation of age with a steeper decline in ERPF in male smokers was lost in multiple regression analysis.

CONCLUSIONS

As compared to women, smoking men may exhibit an increased glomerular hydrostatic pressure, which is a known promoter of kidney damage.

Effect of amlodipine and lisinopril on microalbuminuria in patients with essential hypertension: A prospective study

Microalbuminuria can be present in 25-100% of patients with essential hypertension and is associated with increased incidence of cardiovascular events. Our goal was to evaluate the effect of a commonly used calcium channel blocker, amlodipine, and an angiotensin converting enzyme inhibitor, lisinopril on urinary albumin excretion in patients with mild to moderate essential hypertension. We screened 324 patients with essential hypertension for microalbuminuria and documented it in 120 patients. These 120 patients with microalbuminuria were randomly divided into two groups of 60 each, matched for age, sex, arterial pressure, creatinine clearance, and urinary albumin excretion so as to receive amlodipine or lisinopril. We prospectively measured their urinary albumin excretion and creatinine clearance prior to treatment and, four and eight weeks after treatment with amlodipine or lisinopril. Mean arterial pressure (mean +/- SD) at baseline, after four weeks, and after eight weeks was 113.01 +/- 4.38,104.93 +/- 3.12, and 98.89 +/- 1.75 mmHg (P < 0.0000); and 114.13 +/- 7.11, 106.52 +/- 3.50, and 100.89 +/- 2.80 mmHg (P < 0.0000) in amlodipine and lisinopril groups, respectively. Urinary albumin excretion (mean +/- SEM) at baseline, after four, and after eight weeks was 79.30 +/- 3.74, 62.03 +/- 3.61, and 52.02 +/- 3.05 (P < 0.0000); and 73.96 +/- 4.10, 72.39 +/- 3.74, 66.12 +/- 3.94 (P = 0.1742) in lisinopril and amlodipine groups, respectively. Lisinopril but not amlodipine, reduced the urinary albumin excretion significantly despite their similar antihypertensive efficacy. The clinical and prognostic significance of these observations need to be established.

Blood pressure in relation to the renin-angiotensin-aldosterone system

The relationship between blood pressure (BP) and the renin-angiotensin-aldosterone system was studied in a stratified random sample (n=120) of 49-year-old men selected from a BP screening and covering a wide range of BPs. Only subjects not on antihypertensive treatment were included. None had malignant or secondary hypertension. Plasma renin activity, plasma concentrations of angiotensin II, aldosterone, sodium, potassium and noradrenaline and the 24-hour urinary excretions of sodium, cortisol and noradrenaline were determined. Of these variables, only p-aldosterone was significantly correlated wtih BP, both in the whole study group (R=0.22, p less than 0.02, n=119) and in the subjects with the highest BP range (R=0.36, p less than 0.02, n=30). Of the clinical groups compared, the hypertensive subjects had significantly higher mean p-aldosterone than the borderline and normotensive subjects. Multiple regression analysis showed that the 24-hour urinary excretion of noradrenaline was the factor most strongly correlated to p-aldosterone, suggesting that the sympathetic nervous system might stimulate aldosterone secretion. Our findings indicate that aldosterone may be of importance for the development and maintenance of essential hypertension.

Revisiting normal 51Cr-ethylenediaminetetraacetic acid clearance values in children

PURPOSE

Normal (51)Cr-ethylenediaminetetraacetic acid (EDTA) clearance values as a function of age were published a number of years ago. These values were based on data from children with a normal left to right ratio and a normal appearance on DMSA scintigraphy, despite the presence of an acute renal infection. At that time, the authors were unaware that hyperfiltration is a common phenomenon in patients with acute renal infection and that their normal values could have been significantly overestimated. The present work therefore aimed to re-appraise these normal values.

METHODS

In a first step, in order to verify the previous results, the same type of population was selected, namely patients with present or past urinary tract infection but normal images and a normal left to right ratio on DMSA scintigraphy. In a second step, the selection was based on patients who had had no recent urinary tract infection. In both series, a single blood sample method was used for the evaluation of (51)Cr-EDTA clearance.

RESULTS

In the first group of patients, the results obtained were almost identical to those previously published. In the second group of patients, the results were significantly lower: after 2 years of age, the mean GFR value was 104 ml/min/1.73 m(2) (10th and 90th percentiles 81 and 135 ml/min/1.73 m(2), respectively), compared with 117 ml/min/1.73 m(2) in the first group.

CONCLUSION

The data of the second group are probably more representative of the true normal GFR values and can be applied to the entire paediatric population.

Urinary albumin excretion is related to cardiovascular risk indicators, not to flow-mediated vasodilation, in apparently healthy subjects

Based on studies in diabetic and hypertensive populations it has been postulated that early endothelial dysfunction is the mechanism responsible for the increased cardiovascular risk in microalbuminuric subjects. We evaluated the relation between microalbuminuria and endothelial dysfunction, assessed as flow-mediated dilation of the brachial artery, in an apparently healthy population. Within the framework of the PREVEND Intervention Trial non-hypertensive and non-hypercholesterolemic subjects were recruited on the basis of reproducible microalbuminuria. Using high-resolution ultrasound, flow-mediated dilation and nitroglycerin-mediated dilation of the brachial artery was assessed to measure endothelium-dependent and endothelium-independent responses, respectively. For the current study subjects with diabetes mellitus, clinical atherosclerosis, and macroalbuminuria were excluded from the analyses. We studied 421 men and 233 women (mean age (SD) 50 (12)). Increasing levels of urinary albumin excretion were accompanied by a significant increase in age, percentage men, systolic and diastolic blood pressure, body mass index, and serum triglycerides, whereas there was no decrease of flow-mediated vasodilation or nitroglycerin-mediated vasodilation. Adjusted for age and sex, urinary albumin excretion was significantly related to systolic (r=0.19, P<0.001) and diastolic (r=0.16, P<0.001) blood pressure, body mass index (r=0.18, P<0.001), and triglycerides (r=0.13, P=0.001), but not to flow-mediated vasodilation (r=-0.01, P=0.8). In contrast to blood pressure, body mass index, and triglycerides, there was no relation between urinary albumin excretion and flow-mediated vasodilation in apparently healthy subjects. These data suggest that the presence of atherogenic risk factors precedes the development of endothelial dysfunction in microalbuminuric, but otherwise healthy subjects.

Microalbuminuria as a predictive factor for cardiovascular events

We tested the hypothesis that microalbuminuria screening in a general practice setting would identify high-risk nondiabetic hypertensive patients, and we measured microalbuminuria response to drug treatment. General practitioners were enrolled who had collected medical histories and performed physical examinations and routine laboratory tests in more than 11,000 untreated hypertensive, nondiabetic patients. Microalbuminuria was measured with an albumin-sensitive immunoassay test strip. The patients' mean age was 57 years, 51% were men, and mean duration of hypertension was 69 months. Twenty-five percent of patients had coronary artery disease (CAD), 17% had left ventricular hypertrophy (LVH), 5% had had a stroke, and 6% had peripheral vascular disease (PVD). Microalbuminuria was present in 32% of men and 28% of women. In patients with microalbuminuria, 31% had CAD, 24% had LVH, 6% had had a stroke, and 7% had PVD. In patients without microalbuminuria, all of these rates were significantly lower: 22%, 14%, 4%, and 5%, respectively (p < 0.001). Furthermore, in patients with CAD, LVH, stroke, or PVD, microalbuminuria was significantly greater than in patients who did not have these complications (p < 0.001). A multiple stepwise regression analysis with microalbuminuria as the dependent variable showed microalbuminuria depended on the following factors, in order of importance: systolic blood pressure, retinopathy, CAD, diastolic blood pressure, and LVH (all p < 0.0001). A multiple stepwise regression analysis with each of the concomitant diseases as the dependent variable showed that microalbuminuria was an independent and significant variable for each of the conditions. The patients were assigned to monotherapy with either angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, calcium antagonists, or diuretics. All of the drugs reduced microalbuminuria, although the beta-blocker carvedilol was superior (p < 0.05). We concluded microalbuminuria is an important risk factor that can be influenced by treatment.

Circadian variation of urinary microalbumin excretion and ambulatory blood pressure in patients with essential hypertension

OBJECTIVE

To investigate the relationship between circadian changes in urinary microalbumin excretion (UAE), blood pressure (BP) and physical activity in patients with essential hypertension.

DESIGN AND METHODS

The subjects were 45 patients with essential hypertension (EH group: 26 male and 19 female, age 56+/-12 years (mean +/- SD)) and 25 patients with diabetes mellitus (DM group: 14 male and 11 female, age 61+/-10 years). Their BP and physical activity (acceleration) were measured at 30-min intervals for 24 h by means of a multi-biomedical recorder (TM2425). Urine samples were collected during each of four 4-h daytime periods and one 8-h night-time period. From these samples, per-h UAE (UAE/h) was measured. Mean values for mean blood pressure (MBP) and acceleration were calculated for corresponding time periods. Plasma hormones were measured during an early morning rest period.

RESULTS

In the EH group, a significant positive correlation was observed between circadian variation of UAE/h and MBP in 35 (78%) subjects, and the mean coefficient of correlation (r) was 0.86+/-0.12. A significant positive correlation was observed between circadian variation of UAE/h and mean acceleration value (Gh) in 25 (56%) subjects, and the mean r value was 0.70+/-0.26. Multivariate linear regression analysis showed that MBP exerted a greater influence on UAE/h than Gh. Significant positive correlations were observed between UAE/day and plasma human atrial natriuretic peptide and plasma aldosterone concentration (r = 0.50, P < 0.01; r = 0.36, P< 0.05). None of these relations, however, was observed in the DM group.

CONCLUSIONS

In patients with essential hypertension, circadian changes in activity and variation of BP influence UAE/h, but no definite relationship of this kind was observed in patients with diabetes mellitus. Measurement of circadian changes in UAE or UAE/day may be useful in estimating the degree of daily stress in non-diabetic patients with essential hypertension.

Ambulatory blood pressure and urinary albumin excretion in clinically healthy subjects

A slightly elevated urinary albumin excretion rate (UAER) is a predictor of atherosclerotic cardiovascular disease. The mechanism is unknown, but moderate office blood pressure elevation has been demonstrated as part of a clustering of known atherosclerotic risk factors in subjects with elevated UAER. Because 24-hour ambulatory blood pressure is a superior predictor of hypertensive target organ involvement, we aimed to investigate blood pressure profile in clinically healthy subjects with elevated UAER. Ambulatory blood pressure monitoring was performed with a portable recorder in 27 subjects with an elevated UAER (>6.6 microg/min, overnight urine collection) and 46 normoalbuminuric control subjects. Mean+/-SD systolic and diastolic ambulatory blood pressures (24-hour) were significantly higher in subjects with elevated UAER than in normoalbuminuric controls (134+/-12 versus 128+/-11 mm Hg and 78+/-7 versus 75+/-6 mm Hg, P<0.05), as were systolic and diastolic blood pressure loads [median (range): 42% (6 to 94%) versus 23% (1 to 89%) and 20% (0 to 68%) versus 6% (0 to 62%), P<0.05]. The circadian variation of blood pressure was normal in subjects with elevated UAER. However, the increased urinary loss of albumin could not be solely related to the higher blood pressure. In conclusion, apparently healthy subjects with elevated UAER had slightly but significantly higher 24-hour systolic and diastolic blood pressure levels in addition to increased blood pressure loads but normal circadian variation. The demonstrated differences in blood pressure may offer a partial explanation for the association between elevated urinary albumin excretion and atherosclerotic cardiovascular risk.

Relationship between renal plasma flow response to angiotensin II and blood pressure in a population-based sample

OBJECTIVE

To assess whether interindividual variation in renal plasma flow or in its response to angiotensin II infusion is associated with interindividual differences in blood pressure in a population-based sample of 287 non-Hispanic whites (143 women and 144 men), aged 20-49.9 years.

METHODS

After seven days of eating a high-sodium diet (260 mmol/day), the renal plasma flow was determined by measuring the clearance of p-aminohippurate before and after infusion of 3 ng/kg per min angiotensin II. Multiple linear regression methods were used to assess whether measures of the renal plasma flow and of its response to angiotensin II infusion were predictive of systolic or diastolic blood pressures measured prior to administration of the high-sodium diet, on day 6 of the high-sodium diet, or during the renal clearance procedure on day 7 prior to angiotensin II infusion.

RESULTS

There was some evidence that measures of the renal plasma flow and of its response to angiotensin II infusion during the high-sodium diet were statistically significant predictors of measures of blood pressure in women; there was less evidence for this for blood pressures in men. Interindividual variation in measures of the renal plasma flow and of its response to angiotensin II infusion explained less than 10% of the interindividual variation in any measure of the blood pressure in both sexes.

CONCLUSION

These results suggest that interindividual variation in renal plasma flow ad in its response to angiotensin II infusion during a high-sodium diet will be of limited utility in elucidating the basis for interindividual differences in blood pressure.

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.

Bisoprolol, a once-a-day beta-blocking agent for patients with mild to moderate hypertension

The 24-h blood pressure control of bisoprolol, a new beta-selective, beta-blocking agent, was studied in 240 mild to moderate hypertensive patients in this 4-week, randomized, double-blind, placebo-controlled trial. A once-daily dosing schedule was evaluated by comparing bisoprolol's antihypertensive effectivness and safety at 24 h postdose and 3 h postdose, the latter time intended to correspond to peak effectiveness. Results from this trial demonstrated the antihypertensive effectiveness of once-daily bisprolol at doses ranging from 5-20 mg. Mean reductions from baseline diastolic blood pressure, measured 24 h postdose, were 6.3, 8.8, and 10.1 mmHg for patients receiving bisoprolol 5, 10, and 20 mg, respectively, compared with 1.6 mmHg for placebo-treated patients (p < 0.01); mean reductions from baseline systolic blood pressure for the bisoprolol groups were 8.6, 8.6, and 10.9 mmHg, respectively, versus 3.3 mmHg for placebo (p < or = 0.01); and mean reductions from baseline heart rate for the bisoprolol groups were 5.1, 7.1, and 10.2 beats/min, respectively, compared with a 0.9 beats/min increase in heart rate for the placebo group (p < 0.01). The response rates for bisoprolol-treated patients ranged from 47 to 70% compared with 18% for patients on placebo (p < 0.01). Antihypertensive effects were dose-related and sustained over the 24-h dosing interval. Near maximal antihypertensive effects were achieved within 1 week of initiation of therapy with bisoprolol and were sustained over the course of the trial.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of captopril and nadolol on renal hemodynamics in patients with essential hypertension

The randomized single-blind study was designed to compare the effects of captopril (Cap) and nadolol (Nad) on renal hemodynamics in 60 patients with essential hypertension. They were divided into two groups at random. Cap was given in dosage of 37.5-75 mg/d per os and Nad 40-80 mg/d. The results show that both drugs increase the blood volume distributed to the kidneys from cardiac output (renal blood flow/cardiac output), Cap increasing 10% (P < 0.05) and Nad 8% (P < 0.05). Renal vascular resistance (RVR) is lowered by the two drugs, 13% (P < 0.05) by Cap and 11% (P < 0.05) by Nad. These suggest that both drugs facilitate the maintenance of renal blood circulation in patients with essential hypertension, being beneficial for long-term treatment of hypertension.

Accelerated decline in renal perfusion with aging in essential hypertension

The present cross-sectional study was designed to assess the effect of the severity of hypertensive cardiovascular disease and age on renal hemodynamics. In a homogeneous population of 157 white men (aged 15 to 87 years), we assessed renal and systemic hemodynamics by measuring mean arterial pressure invasively, renal blood flow by 131I-para-aminohippuric acid clearance, and cardiac output by the indocyanine dye dilution technique. Stepwise multiple regression analysis revealed the following independent determinants of renal blood flow: age (beta = -.42, P < .001), height (beta = +.14, P < .03), mean arterial pressure (beta = -.15, P < .02), and cardiac output (beta = +.19, P < .008). Renal blood flow corrected for height correlated inversely with age in all three groups. However, the renal fraction of cardiac output did not correlate with age in borderline hypertension (r = .17, P = NS) and in normotension (r = .12, P = NS), suggesting a parallel decline in renal blood flow and cardiac output with aging. In contrast, in established hypertension, the renal fraction of cardiac output was closely linked to age (r = .52, P < .001) and significantly steeper (P < .01) than in normotension or borderline hypertension. We conclude that unlike in normotensive subjects or patients with borderline hypertension, patients with established hypertension have an accelerated decline in renal perfusion with aging, reflecting selective functional or structural changes or both in the renal vascular bed.

Renal hemodynamics and cardiovascular reactivity in the prehypertensive stage

To examine whether sympathetic nervous activation has an impact on renal circulation in subjects at risk for high blood pressure, we assessed renal hemodynamics and cardiovascular response to mental stress in 40 healthy young white males, 12 normotensive subjects without and 14 with familial hypertension, and 14 with borderline hypertension. The response of systolic and diastolic blood pressure to mental stress was assessed while each patient performed a mental arithmetic task; this was taken as the parameter for the activation of the sympathetic nervous system. Renal plasma flow was measured by para-aminohippuric acid clearance under steady-state conditions. In parallel, glomerular filtration rate as a parameter for functional impairment of the kidneys was determined by creatinine clearance, and filtration fraction was also calculated. Patients with borderline hypertension were characterized by a reduced renal blood flow and increased filtration fraction in comparison with both normotensive groups. The increase in systolic blood pressure during mental stress was more pronounced in borderline hypertensives. We observed no significant difference in renal hemodynamics and cardiovascular response to mental stress between normotensives with and without a family history of hypertension. In the total population, cardiovascular response to mental stress was correlated with renal hemodynamics: The greater the increase in systolic blood pressure during mental stress, the lower was the renal plasma flow and the greater the filtration fraction. Thus, renal plasma flow was found to be already reduced and filtration fraction increased before sustained hypertension developed. Because this pattern in renal hemodynamics was related to cardiovascular response to mental stress, our data suggest that sympathetic activation already appeared to affect renal hemodynamics at the onset of essential hypertension.

A comparative study of lisinopril and atenolol on low degree urinary albumin excretion, renal function and haemodynamics in uncomplicated, primary hypertension

The presence of slightly increased urinary albumin excretion (UAE), even at levels well below levels detectable by an ordinary dipstick, has been suggested as a predictor of cardiovascular morbidity and as a reflection of the degree of overall vascular permeability. The aim of the present investigation was to study the effects of two different antihypertensive drug regimens, an ACE inhibitor and a beta-adrenoceptor antagonist, on the low UAE rate observed in subjects with uncomplicated, mild to moderate primary hypertension. After a 4-week placebo run-in period, 49 patients (mean age 54 y) were randomly assigned in a double blind manner either to further 4 weeks on placebo (P, n = 15), 8 weeks on lisinopril (L, n = 17; 20 mg/40 mg o.d.) or 8 weeks on atenolol (A, n = 17; 50 mg/100 mg o.d.). The 24-h UAE was measured every second week. At entry and after 4 weeks the glomerular filtration rate and the renal plasma flow were measured. Both drugs lowered blood pressure (BP) to a similar extent after 4 and 8 weeks of treatment; the blood pressures were 160/106 (P), 159/104 (L) and 154/103 (A) at entry, and 133/83 (L) and 134/87 (A) at the end of the study after 8 weeks. On entry the 24-h UAE in all patients ranged from 4 to 49 mg (mean 14.1 mg), and it did not differ significantly between groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Microalbuminuria in patients with essential hypertension: effects of several antihypertensive drugs

PURPOSE

Microalbuminuria can be present in 10% to 40% of patients with essential hypertension and is associated with an increased incidence of cardiovascular events. The effect of commonly used antihypertensive agents on urinary albumin excretion (UAE) has not been well established. The aim of this study was to evaluate the effects of a converting enzyme inhibitor, a calcium channel blocker, a beta blocker, and a diuretic on UAE and on creatinine clearance in patients with mild to moderate hypertension.

PATIENTS AND METHODS

We prospectively measured UAE prior to and 4 and 8 weeks after treatment with enalapril, nitrendipine, atenolol, or a diuretic in 48 patients with essential hypertension and microalbuminuria.

RESULTS

All these agents were equally effective in reducing arterial pressure. However, enalapril but not the other agents significantly decreased UAE.

CONCLUSION

Eight weeks of therapy with enalapril may reduce UAE in patients with mild to moderate essential hypertension, whereas other agents, such as nitrendipine, atenolol, or diuretics, had no measurable effect on UAE. The clinical and prognostic significance of these observations remains to be established.

Renal function in severe congestive heart failure during treatment with enalapril (the Cooperative North Scandinavian Enalapril Survival Study [CONSENSUS] Trial)

The effect on renal function of long-term treatment with either enalapril (n = 123) or placebo (n = 120) in addition to conventional therapy was studied in a randomized trial in patients with severe congestive heart failure (New York Heart Association functional class IV; the Cooperative North Scandinavian Enalapril Survival Study). Enalapril was administered in a dose of 2.5 to 40 mg/day. The analysis was restricted to the first 6 months of treatment. There was an average initial increase of 10 to 15% (10 to 20 mumol/liter) irrespective of baseline serum creatinine within the first 3 weeks of enalapril treatment, whereafter mean serum creatinine remained on a similar level during the first 6 months. Enalapril was well-tolerated by most patients, and serum creatinine was reduced in 24%. Serum creatinine increased by greater than 100% in 13 patients (11%) in the enalapril group (mainly as a consequence of intercurrent disease or severe hypotension, and usually transiently) and in 4 (3%) in the placebo group. The maximal increase in serum creatinine in the enalapril group was inversely correlated to the diastolic blood pressure (p = 0.008) at baseline and to the mean diastolic and systolic blood pressures measured at the time of the maximal increase in serum creatinine (p = 0.0001). According to multivariate regression analysis, the maximal increase in serum creatinine was also slightly influenced by the dose of furosemide taken. The development of hypotension emerged as the strongest factor explaining an abnormal increase in serum creatinine.(ABSTRACT TRUNCATED AT 250 WORDS)

ACE inhibitors in renal disease

Recent experimental studies suggest that the resistance state of the preglomerular and postglomerular capillary arterioles may determine if a particular class of antihypertensive agents will protect the kidney from hemodynamically mediated glomerular injury. This review discusses (1) the effects of angiotensin II on the renal microcirculation, (2) the pathophysiology of essential hypertensive renal disease, (3) the renal pharmacology of angiotensin-converting enzyme (ACE) inhibitors, and (4) the hypothesis that renal protection is dependent on control of systemic and glomerular hypertension.

The aging hypertensive kidney: pathophysiology and therapeutic options

The aging kidney undergoes hemodynamic changes characterized by reductions in glomerular filtration rate and effective renal plasma flow. These functional changes are associated with loss of renal mass related to changes in the intrarenal vasculature. The reduced glomerular filtration surface area and subsequent microcirculatory adaptations enhance the risk for development of renal diseases associated with systemic diseases. Hypertensive nephrosclerosis accounts for 26% of all end-stage renal disease in the United States; the median age of those affected is 67 years. Hemodynamic and structural changes observed in the essential hypertensive kidney suggest an accentuation of the physiologic aging process. Initially observed hemodynamic changes, which may be reversible with specific drug therapy, suggest that excessive production of angiotensin II plays a role. Progressive renal impairment may occur despite control of systemic hypertension. Renal protection appears to require therapeutic normalization of both systemic and glomerular capillary pressures. The latter may depend on a drug's ability to attenuate the intrarenal effects of angiotensin II on the renal microcirculation. Drug classes with renal protective potential include angiotensin-converting enzyme inhibitors and calcium antagonists. However, long-term clinical trials are required to assess the potential advantages of specific drug therapies in preventing the development and/or progression of hypertensive arteriolar nephrosclerosis.

Nutritional causes of renal impairment in old age

The occurrence of renal insufficiency tends to increase in late adulthood. This common complication of old age is associated with increased physical dependency, morbidity, and mortality, and a lowered quality of life. In this review, the authors will develop the thesis that dietary practices during early and middle adulthood importantly influence the risk of renal insufficiency in the elderly.

Acute and chronic effects of angiotensin converting enzyme inhibitors on the essential hypertensive kidney

The natural course of essential hypertensive renal disease is characterized by a slowly progressive impairment of renal function. Initially, the changes are functional and reversible; however, structural changes gradually occur, leading to hypertensive nephrosclerosis. Similarities exist between the early functional hemodynamic changes observed in the essential hypertensive kidney and the physiologic renal effects of angiotensin II. To the degree that the initial functional changes are the result of excessive endogenous production of angiotensin II, interruption of the integrity of this humoral system could be expected to reverse the pathophysiologic sequence of events leading to hypertensive nephrosclerosis. This review focuses on the pathophysiology of the essential hypertensive kidney, the intrarenal effects of angiotensin II, and the acute and chronic effects of angiotensin converting enzyme (ACE) inhibition therapy on the essential hypertensive kidney. The data reviewed suggest that ACE inhibition therapy does reverse the initial functional hemodynamic changes observed in the essential hypertensive kidney and may protect the glomerulus from hemodynamically mediated injury.

Renal function in an elderly population. A study of S-creatinine, 51Cr-EDTA clearance, endogenous creatinine clearance and maximal tubular water reabsorption

There has been reported a decline in renal function with age, a decline that seems to accelerate after the age of 50. A systemically chosen sample of 70- and 75-year-old probands from the study '70-year-olds in Göteborg' have previously been examined with respect to GFR. The present study is a longitudinal follow-up of GFR in the previously examined 75-year-old probands at age 79. Renal tubular water absorption was also determined. In order to make a longitudinal comparison, S-creatinine was determined in a subsample of 166 probands, who had attended the study at 70, 75 and 79 years of age, by using frozen sera from these three examinations. S-creatinine increased slightly but statistically significant in both sexes between 70 years and 79 years of age. The reference values for EDTA clearance at age 79 calculated as M +/- 2 SD were 46-94 ml/min X 1.73 m2 BSA without any difference between the sexes. There was no change in GFR between 75 years and 79 years of age. We did not find any correlation between EDTA clearance and creatinine clearance. The tubular water reabsorption for probands without disorders was 843 +/- 92.6 (range 709-982). The results suggest that the renal filtration rate at age 79 is still good and that the ageing of the tubular function is not as pronounced as that of the GFR.

Diastolic function of the heart in untreated primary hypertension

To study left ventricular (LV) diastolic function of the heart in relation to blood pressure (BP) and other signs of hypertensive cardiac and peripheral vascular changes, isovolumic relaxation time and early diastolic filling were determined in four BP groups of untreated 49-year-old men: normotensive subjects (n = 20), men with borderline hypertension (n = 30), mild hypertension (n = 45), and moderate to severe hypertension (n = 24). Isovolumic relaxation time, measured as the distance between aortic closure (A2, phonocardiography) and mitral valve opening (echocardiography), and early diastolic filling, measured as the distance between mitral valve opening and the O point of the apexcardiogram, tended to increase with BP level, and the total interval from aortic closure to the O point (A2O interval) was significantly prolonged in the two groups with mild and moderate to severe hypertension. A prolonged A2O interval (greater than or equal to 117% of expected value at observed heart rate) was seen in several hypertensives, who had no obvious increase in LV wall thickness on M mode echocardiography. This suggests that a prolonged LV relaxation time may be an early sign of cardiac involvement in primary hypertension. In the group with moderate to severe hypertension, an increase in LV wall thickness was seen together with an increase in resistance at maximal dilation in the calf. This supports the theory that when changes in cardiac structure develop they occur in parallel with structural changes also in the periphery.

Effects of subpressor doses of angiotensin II on renal hemodynamics in relation to blood pressure

The renal hemodynamic response to subpressor doses of angiotensin II (AII; 0.1 and 0.5 ng/min/kg) was investigated in untreated 49-year-old men (n = 50) representing a wide blood pressure range. Renal blood flow, renal vascular resistance (RVR), glomerular filtration rate (GFR), filtration fraction (FF), plasma renin activity (PRA), plasma AII, plasma aldosterone, and the urinary excretion of sodium and norepinephrine were studied. The higher the initial blood pressure the greater was the increase in RVR in response to AII infusion (p less than 0.002), indicating an increased renal vascular reactivity with increase in initial blood pressure. The AII infusion gave a significant rise in RVR in both the borderline and hypertensive group, but gave no increase in RVR in the normotensive group, implying an enhanced sensitivity of the renal vasculature in the borderline and hypertensive group. The increase in RVR was greater in the hypertensive than in the borderline group, i.e., the hypertensives had a steeper dose-response curve than the borderline group, which points to the presence of structural vascular changes in the renal vessels in the hypertensives. The increase in RVR in response to AII was positively correlated to sodium intake and plasma aldosterone concentration, indicating that these two factors might modulate the renal vascular reactivity. These factors could, however, only partly explain that RVR increased more the higher the initial blood pressure. Thus, the results indicate that there is an increased reactivity of the renal vascular bed to AII in essential hypertension. The increased reactivity seems to be mediated through an increased sensitivity of the renal vasculature to AII in mild essential hypertension and also through the presence of structural vascular changes in established hypertension. These factors may lead to a reduced excretion of sodium and water and may therefore be of importance in the development and progression of essential hypertension.

Age-dependent alterations in the structurally determined vascular resistance, pre- to postglomerular resistance ratio and glomerular filtration capacity in kidneys, as studied in aging normotensive rats and spontaneously hypertensive rats

Maximally dilated renal vascular beds of 13-month-old NCR and SHR were compared to explore how aging respectively longstanding primary hypertension structurally alters total renal resistance, pre/postglomerular resistance ratio and maximal glomerular filtration capacity, as measured per unit kidney weight. According to comparisons of 1.5- and 3.5-month-old NCR and SHR (Folkow et al. 1977), a structurally increased pre/postglomerular resistance ratio rapidly resets the renal "longterm barostat function" in SHR to match the 30-40% pressure rise, thereby increasing total renal resistance 15-20%, while filtration capacity is unaltered so far. In NCR aging to 13 months hardly alters arterial pressure, but increases total renal resistance 10-15%, mainly affecting postglomerular vessels, while filtration capacity is reduced 25%. 13-month-old SHR show an additional 15% pressure rise and--relative to agematched NCR--a further 35% reduction of filtration capacity with a 30-35% increase of total renal resistance, which mainly affects the postglomerular vessels as the resistance ratio is now barely above that in NCR. Thus, advancing SHR hypertension seems to start a renal vicious circle, because accentuated reductions of filtration capacity are parallelled by structural postglomerular resistance increases apparently to maintain GFR by raised filtration pressure which, however, accelerates glomerular deterioration.

Type of obesity and blood pressure

To explore the relationship between blood pressure on the one hand and body composition variables and fat cell size and number on the other, these factors were determined in a population sample (n = 120) of 49-year-old men with blood pressure (BP) ranging from very low to very high. BP increased linearly with body weight throughout the entire BP range, while body fat and fat cell size increased with increasing BP in the nonhypertensive but not in the hypertensive BP range. Body cell mass and fat cell number were unrelated to BP. Fat cell size (but not fat cell number) was positively correlated with most variables of glucose metabolism. It can be concluded that in normal men: the previously well-established relationship between body weight and BP is explained by an association between body fat and BP; BP is positively correlated with increased fat cell size, indicating hypertrophic obesity, while BP is unrelated to fat cell number; and increased fat cell size is associated with impaired glucose tolerance and hyperinsulinemia. The results point to the possibility that hypertrophic obesity and essential hypertension may be related to each other via common pathogenetic mechanisms.

Reference values for 51Cr-EDTA clearance as a measure of glomerular filtration rate

Reference values for glomerular filtration rate (GFR) were defined using eight reports including epidemiological studies and studies in kidney donors. Studies using both inulin and 51Cr-EDTA were included. GFR decreased with age, by 4 ml/min decade below the age of 50, and 10 ml/min decade above 50 years of age. No sex difference was found. +/- 2 SD was equal to 25 ml/min at all ages. Based on these findings a nomogram for GFR is presented. Emphasis is given to the use of plasma clearance of 51Cr-EDTA estimated with single injection technique as the new reference method for GFR measurement.