HMG-CoA reductase inhibitors and the kidney

During the last two decades, numerous studies have demonstrated that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) diminish the risk of cardiovascular morbidity and mortality. Although these studies have focused primarily on the ability of statins to lower circulating levels of low-density lipoprotein cholesterol, more recent research has shown that statins may protect the vasculature via pleiotropic effects not directly related to lipid lowering. These include adjustments in cell-signaling pathways that play a role in atherogenesis and that affect the expression of inflammatory elements, curtail oxidative stress, and enhance endothelial function. More recently, researchers have begun to explore whether these agents exert similar beneficial effects in renal parenchymal and renovascular disease. This review examines the available evidence that dyslipidemia may augment the inflammatory reaction of cytokines in patients with renal disease and that statins may improve renal dysfunction by altering the response of the kidney to dyslipidemia, even in persons with end-stage renal disease on dialysis or with renal transplantation. In this context, some data suggest that statin-mediated alterations in inflammatory responses and endothelial function may reduce proteinuria and the rate of progression of kidney disease.

Long-term effects of spironolactone on proteinuria and kidney function in patients with chronic kidney disease

Experimental evidence suggests that aldosterone contributes to progressive kidney disease. Angiotensin-converting enzyme inhibitors and angiotensin type 1 receptor antagonists suppress the renin-angiotensin system but they do not effectively reduce plasma aldosterone. Hence, administration of aldosterone receptor antagonists may provide additional renal protection. In the present prospective randomized open-label study, we evaluated the effects of spironolactone (25 mg/day for 1 year) on proteinuria and estimated glomerular filtration rate in 83 patients with chronic kidney disease already treated with angiotensin-converting enzyme inhibitors and/or angiotensin type 1 receptor antagonists. Eighty-two patients were treated with angiotensin-converting enzyme inhibitors and/or angiotensin type 1 receptor antagonists alone and served as controls. After 1 year of therapy, proteinuria decreased from 2.1+/-0.08 to 0.89+/-0.06 g/g creatinine (P<0.001) in patients treated with spironolactone, but it did not change in control patients. Baseline aldosterone levels were significantly correlated with proteinuria (r=0.76, P<0.0001), and predicted the degree of reduction in proteinuria with spironolactone (r=0.42, P<0.0002). Baseline estimated glomerular filtration rate was similar in patients treated with spironolactone and controls (62.4+/-2.4 and 62.2+/-2.1 ml/min/1.73 m(2), respectively). After 1 month of therapy with spironolactone, estimated glomerular filtration rate decreased more in patients treated with spironolactone than in controls. However, by the end of 1 year the monthly rate of decrease in estimated glomerular filtration rate from baseline was lower in patients treated with spironolactone than in controls (0.323+/-0.044 vs 0.474+/-0.037 ml/min/1.73 m(2), P<0.01). Spironolactone caused a significant rise in serum potassium levels (from 4.2+/-0.04 at baseline to 5.0+/-0.05 mEq/l after 12 months of treatment, P<0.001). In conclusion, this study has shown that spironolactone may reduce proteinuria and retard renal progression in chronic kidney disease patients.

Hypertension in renal parenchymal disease: why is it so resistant to treatment?

The association between hypertension and chronic renal disease is well known. The pathogenesis of hypertension in patients with chronic kidney disease (CKD) is complex and multifactorial, which may explain why it is resistant to treatment. The traditional paradigm is that hypertension in CKD is due either to an excess of intravascular volume (volume dependent) or to excessive activation of the renin-angiotensin system in relation to the state of sodium/volume balance (renin-dependent hypertension). This review focuses on the importance of less established mechanisms, such as increased activity of the sympathetic nervous system, increased endothelin production, decreased availability of endothelium-derived vasodilators and structural changes of the arteries, renal ischemia, and sleep apnea.

Silent ischemia is more prevalent among hypertensive patients with microalbuminuria and salt sensitivity

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). Salt-sensitive hypertensives also manifest greater UAE compared to salt-resistant individuals. Although the significance of these associations is not well established, several lines of evidence suggest that microalbuminuria and/or salt sensitivity may be associated with greater prevalence of cardiovascular risks and events. In this study, we have evaluated by ergometric exercise 42 subjects with microalbuminuria and 42 matched individuals with normal UAE. All these subjects also underwent a standardized protocol to determine blood pressure sensitivity to a high salt intake. Patients with microalbuminuria displayed greater levels of ambulatory blood pressure and a greater rise in systolic blood pressure during exercise compared to patients with normal UAE (33.1 +/- 1.56 vs 26.4 +/- 1.7 mmHg, P < 0.001). Seven hypertensive patients with microalbuminuria developed ST segment depression during exercise compared to only one subject with normal UAE. Salt-sensitive patients manifested greater UAE than salt-resistant subjects (58 and 14 mg, 24 h, P < 0.001) and greater prevalence of silent ischemia (6 vs 2) than salt-resistant individuals. In conclusion, these studies have shown that hypertensive individuals with microalbuminuria and/or salt sensitivity manifest an increased prevalence of silent ischemia.

Omapatrilat versus lisinopril: efficacy and neurohormonal profile in salt-sensitive hypertensive patients

Omapatrilat, a vasopeptidase inhibitor, simultaneously inhibits neutral endopeptidase and ACE. The efficacy and hormonal profile of omapatrilat and lisinopril were compared in salt-sensitive hypertensive patients. On enrollment, antihypertensive medications were withdrawn, and patients received a single-blind placebo. On day 15, salt-sensitivity determinations were made. Salt-sensitive hypertensive patients returned within 5 to 10 days for baseline evaluations of ambulatory diastolic blood pressure, ambulatory systolic blood pressure, and atrial natriuretic peptide. Salt-sensitive hypertensive patients were randomized to receive double-blind omapatrilat (n=28) or lisinopril (n=33) at initial doses of 10 mg for 1 week, increasing to 40 and 20 mg, respectively, for an additional 3 weeks. Ambulatory blood pressure and urinary atrial natriuretic peptide were assessed at study termination. Both omapatrilat and lisinopril significantly reduced mean 24-hour ambulatory diastolic and systolic blood pressures; however, omapatrilat produced significantly greater reductions in mean 24-hour ambulatory diastolic blood pressure (P=0.008), ambulatory systolic blood pressure (P=0.004), and ambulatory mean arterial pressure (P=0.005) compared with values from lisinopril. Both drugs potently inhibited ACE over 24 hours. Omapatrilat significantly (P<0.001) increased urinary excretion of atrial natriuretic peptide over 0- to 24-hour (3.8-fold) and 12- to 24-hour (2-fold) intervals; lisinopril produced no change. Omapatrilat significantly (P<0.001) increased urinary excretion of cGMP over the 0- to 24- and 4- to 8-hour intervals compared with that from lisinopril. Neither drug had a diuretic, natriuretic, or kaliuretic effect. In conclusion, in salt-sensitive hypertensive patients, omapatrilat demonstrated the hormonal profile of a vasopeptidase inhibitor and lowered ambulatory diastolic and systolic blood pressures more than lisinopril.

Interleukin-1beta and neurogenic control of blood pressure in normal rats and rats with chronic renal failure

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). The rise in central SNS activity is mitigated by increased local expression of neuronal nitric oxide synthase (NOS) mRNA and NO(2)/NO(3) production. Because interleukin (IL)-1beta may activate nitric oxide in the brain, we have tested the hypothesis that IL-1beta may modulate the activity of the SNS via regulation of the local expression of neuronal NOS (nNOS) in the brain of CRF and control rats. To this end, we first found that administration of IL-1beta in the lateral ventricle of control and CRF rats decreased blood pressure and norepinephrine (NE) secretion from the posterior hypothalamus (PH) and increased NOS mRNA expression. Second, we observed that an acute or chronic injection of an IL-1beta-specific antibody in the lateral ventricle raised blood pressure and NE secretion from the PH and decreased NOS mRNA abundance in the PH of control and CRF rats. Finally, we measured the IL-1beta mRNA abundance in the PH, locus coeruleus, and paraventricular nuclei of CRF and control rats by RT-PCR and found it to be greater in CRF rats than in control rats. In conclusion, these studies have shown that IL-1beta modulates the activity of the SNS in the central nervous system and that this modulation is mediated by increased local expression of nNOS mRNA.

Neurogenic factors and hypertension in renal disease

Hypertension in chronic renal failure (CRF) is very common and contributes to morbidity and mortality and to the progression of renal disease. The pathogenesis of hypertension in CRF has been attributed mostly to sodium retention and to activation of the renin-angiotensin-aldosterone system. More recently an abundance of evidence has accumulated to support a role for increased sympathetic nervous system (SNS) activity in the genesis of hypertension associated with CRF. Evidence from our laboratory has also demonstrated that the rise in central SNS activity is mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NO) production, and that the upregulation of NO production in the brain is mediated by IL-1beta.

Losartan reduces sympathetic nerve outflow from the brain of rats with chronic renal failure

Sympathetic nervous system (SNS) activity, measured by norepinephrine (NE) turnover rate, was greater in the posterior hypothalamic (PH) nuclei, the paraventricular nuclei (PVN), and the locus coeruleus (LC) of 5/6 nephrectomised (CRF) rats than of control rats. NE secretion from the PH was also greater in CRF than in control rats. These findings demonstrate that SNS activity plays an important role in the genesis of hypertension associated with CRF. The increase in central SNS activity was mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NOx) production. Because angiotensin II may stimulate the central SNS, we tested the hypothesis that losartan, a specific angiotensin II AT(1)-receptor antagonist, may lower blood pressure (BP), at least in part, by central noradrenergic inhibition. To this end, we studied two groups of CRF rats. One group received losartan (10 mg/kg body weight) in drinking water between the 3rd and 4th week after nephrectomy, the second group received drinking water without losartan. SNS activity was measured by NE secretion from the PH using the microdialysis technique. NOS-mRNA gene expression was also measured by RT-PCR in the PH, PVN, and LC of CRF and control rats. Losartan reduced systolic BP from 184+/-3.7 to 152+/-3.1 mmHg and NE secretion from the PH from 340+/-9.7 to 247+/-4.8 pg/ml. CRF rats treated with losartan manifested a significant (p<0.01) increase in the expression of nNOS-mRNA in the PH (from 84+/-1.2 to 99+/-2.6), the PVN (from 44+/-1.5 to 63+/-2.1), and the LC (from 59+/-6.7 to 76+/-2.1). CRF rats also manifested a significant increase (p<0.01) in the expression of IL-1beta the PH (from 41.6+/-2.8 to 54.3+/-1.4), PVN (from 44+/-1.9 to 54+/-1.5), and LC (from 35.5+/-1.6 to 53.5+/-1.9). In conclusion, these studies suggest that the antihypertensive action of losartan in CRF rats may be mediated, at least in part, by inhibition of central SNS outflow. The studies also suggest that the inhibitory action of losartan on the SNS may be mediated by activation of IL-1beta, which, in turn, stimulates nNOS, an important modulator of central SNS activity.

The kidney and the neurogenic control of blood pressure in renal disease

Hypertension is very common in patients with chronic renal failure (CRF) and it contributes to morbidity and mortality as well as to the progression of renal disease. Several mechanisms may play a role in the pathogenesis of hypertension in CRF, but the best known are sodium retention and activation of the renin-angiotensin-aldosterone system. More recently, evidence has accumulated to support a role for increased sympathetic nervous system (SNS) activity in the genesis of hypertension associated with CRF. Our laboratory findings indicate that specific renal injuries, caused by 5/6 nephrectomy and/or phenol injection in the kidney, activate renal afferent pathways that connect with integrative structures in the brain involved in the regulation of SNS activity and blood pressure. This results in a rise in blood pressure sustained by noradrenergic mechanisms. Our laboratory has also shown that the rise in central SNS activity is mitigated by increased local expression of nitric oxide synthase (NOS)-mRNA and nitric oxide (NO) production, and by upregulation of interleukin-1beta.

Diagnosis and evaluation of secondary hypertension

Although patients with secondary hypertension comprise only a small percentage of those with elevated blood pressure, this subgroup should not be ignored. In many cases, correcting the cause of secondary hypertension can lead to a cure, thus avoiding the need for long-term medical therapy, with its attendant risks and economic toll. Moreover, effective treatment of secondary hypertension can prevent chronic complications, such as left ventricular hypertrophy and coronary artery disease, which markedly increase morbidity and mortality. Nearly all forms of secondary hypertension are related to decreased renal function and/or derangement of hormonal balance or secretion. If hypertension is secondary to chronic renal failure of any etiology, it can be recognized from biochemical assays for blood urea nitrogen and creatinine.

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.

Association between hyperlipidemia and microalbuminuria in essential hypertension

BACKGROUND

Some patients with essential hypertension manifest greater than normal urinary albumin excretion (UAE). A few retrospective studies have suggested that there is an association between microalbuminuria and cardiovascular risk. The reasons for this association are not well established, and they are the object of this review.

RESULTS

We found that hypertensive patients with microalbuminuria manifest greater levels of blood pressure, particularly at night. Serum levels of cholesterol, triglycerides, and uric acid in patients with microalbuminuria were higher than levels in those with normal UAE, whereas levels of high-density lipoprotein cholesterol in patients with microalbuminuria were lower than levels in patients with normal UAE. Patients with microalbuminuria manifest a greater incidence of insulin resistance, and thicker carotid arteries. After a follow-up of seven 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 logistical regression analysis showed that UAE, cholesterol level and diastolic blood pressure were independent predictors of the cardiovascular outcome. The rate of clearance of creatinine from patients with microalbuminuria decreased more than did that from those with normal urinary albumin excretion.

CONCLUSIONS

These studies suggest that hypertensive individuals with microalbuminuria manifest a variety of biochemical and hormonal derangements with pathogenic potential, which result in greater incidence of cardiovascular events and a greater decline in renal function than do patients with normal UAE.

Dietary salt intake, blood pressure and the kidney in hypertensive patients with non-insulin dependent diabetes mellitus

The mechanisms responsible for hypertension in NIDDM patients are only partially understood. Increased sensitivity to dietary salt intake and to vasoconstrictor hormones are among the mechanisms proposed. We have studied 19 hypertensive NIDDM patients 7 salt-sensitive and 12 salt-resistant while they were ingesting a diet with 20 mEq/day of Na+ for 9 days and while they were ingesting a diet containing 250 mEq/day of Na+ for 14 days. During the last 4 days of each dietary regimen, they received 60 mg/day of slow-release nifedipine. Blood pressure response to increasing doses of norepinephrine and angiotensin II was studied at the end of each of the four phases of the study. High salt intake increased blood pressure and decreased heart rate in these patients. High salt intake also increased the vascular response to norepinephrine but not to angiotensin II in NIDDM hypertensive subjects. Glomerular filtration rate and renal blood flow were not different during the low and high salt diets. There were no differences in the blood pressure response to norepinephrine or angiotensin II, nor in renal hemodynamic changes among salt-sensitive and salt-resistant NIDDM patients. Nifedipine decreased blood pressure equally in salt-sensitive and salt-resistant hypertensive patients and during the high and the low salt intake. Nifedipine increased renal blood flow, both in salt-sensitive and in salt-resistant individuals, but the differences did not reach statistical significance. Nifedipine decreased the blood pressure response to both norepinephrine and angiotensin II. The studies indicate that an increased reactivity to the pressor action of norepinephrine may contribute to the maintenance of hypertension in NIDDM hypertensive subjects and high salt intake may aggravate the pressor responsiveness to norepinephrine in these patients. Nifedipine is an effective antihypertensive drug in NIDDM patients and its action may be in part related to a decrease in pressor response to norepinephrine and angiotensin II.

Microalbuminuria predicts cardiovascular events and renal insufficiency in patients with essential hypertension

BACKGROUND

Some patients with essential hypertension manifest greater than normal urinary excretion of albumin (UAE). Authors of a few retrospective studies have suggested that there is an association between microalbuminuria and cardiovascular risk.

OBJECTIVE

To evaluate whether microalbuminuria is associated with a greater than normal risk of cardiovascular and renal events.

METHODS

We performed a retrospective cohort analysis of 141 hypertensive individuals followed up for approximately 7 years. Hypertensive patients were defined as having microalbuminuria if the baseline average UAE of three urine collections was in the range 30-300 mg/24 h.

RESULTS

Fifty-four patients had microalbuminuria and 87 had normal UAE. At baseline, the two groups were similar for age, weight, blood pressure, and rate of clearance of creatinine. Serum levels of cholesterol, triglycerides, and uric acid in patients with microalbuminuria were higher than levels in those with normal UAE, whereas levels of high-density lipoprotein cholesterol in patients with microalbuminuria were lower than levels in patient with normal UAE. During follow-up, 12 cardiovascular events occurred among the 54 (21.3%) patients with microalbuminuria and only two such events among the 87 patients with normal UAE (P < 0.0002). Stepwise logistic regression analysis showed that UAE (P = 0.003), cholesterol level (P = 0.047) and diastolic blood pressure (P = 0.03) were independent predictors of the cardiovascular outcome. Rate of clearance of creatinine from patients with microalbuminuria decreased more than did that from those with normal UAE (decrease of 12.1 +/- 2.77 versus 7.1 +/- 0.88 ml/min, P < 0.03).

CONCLUSIONS

This study suggests that hypertensive individuals with microalbuminuria manifest a greater incidence of cardiovascular events and a greater decline in renal function than do patients with normal UAE.

A limited renal injury may cause a permanent form of neurogenic hypertension

Previously, we have shown that an acute injury to the kidney produced by an intrarenal injection of phenol causes an immediate increase in blood pressure and in norepinephrine (NE) secretion from the posterior hypothalamus. The studies suggest that in this model afferent impulses from the kidney to central integrative structures in the brain may be responsible for the increase in blood pressure. To further evaluate whether a renal injury caused by the intrarenal injection of phenol leads to a permanent elevation of blood pressure and whether this is mediated by increased sympathetic nervous system activity, we examined the chronic effects (4 weeks) of an intrarenal injection of 50 microL of 10% phenol on blood pressure and NE secretion from the posterior hypothalamus. Systolic blood pressure increased from 128 +/- 2.1 to 176 +/- 1.5 mm Hg (P < .01) 4 weeks after receiving the intrarenal injection of phenol, but it did not change in rats that received the vehicle (128 +/- 2.4 and 135 +/- 1.7 mm Hg) and in rats that were subjected to renal denervation (127 +/- 3.4 and 124 +/- 1.0 mm Hg). The secretion of NE from the posterior hypothalamic nuclei was greater (P < .01) in rats that received phenol (253 +/- 9.6 pg/mL) than in controls (158 +/- 8.6 pg/mL) and denervated rats (170 +/- 2.1 pg/mL). These studies have shown that a limited injury to one kidney may cause a permanent elevation of blood pressure and this is associated with increased sympathetic nervous system activity.

Hyperinsulinemia, circadian variation of blood pressure and end-organ damage in hypertension

BACKGROUND

Some patients with essential hypertension display hyperinsulinemia and/or insulin resistance. A relationship between hyperinsulinemia and blood pressure has not been conclusively established. Some evidence points to a relationship between hyperinsulinemia and evidence of cardiovascular damage.

OBJECTIVES

In this study, we examined the relationship between insulin secretion in response to an oral glucose load, circadian variation of blood pressure, and evidence of vascular damage, measured by the thickness of the carotid artery and urinary albumin excretion.

DESIGN

Seventy patients with essential hypertension and 35 healthy volunteers were included in the study.

RESULTS

Twenty patients were hyperinsulinemic. Office blood pressure was not different between hypertensive patients with high and those with normal insulin AUC. However, night-time diastolic blood pressure was greater in hypertensive patients with high insulin AUC (93 +/- 2.9 mm Hg) than in those with normal insulin AUC (83.5 +/- 1.7 mm Hg, P < 0.005). The thickness of the carotid artery and urinary albumin excretion were greater (P < 0.05) in patients with high insulin AUC than in patients with normal insulin AUC and normotensive subjects. Insulin AUC was significantly correlated with ambulatory blood pressure, carotid artery thickness, and urine albumin excretion. Multiple regression analysis using insulin AUC as the dependent variable and UAE, triglycerides, body-mass index and office or ambulatory blood pressure as independent variables showed the strongest correlation with urine albumin excretion (P < 0.0001), triglycerides (P < 0.02) and body-mass index (P < 0.07).

CONCLUSIONS

These data suggest that in patients with essential hypertension hyperinsulinemia is associated with higher levels of nocturnal blood pressure, and greater evidence of vascular damage.

Effect of L-arginine on systemic and renal haemodynamics in salt-sensitive patients with essential hypertension

In response to a high sodium (Na+) intake, salt-sensitive patients with hypertension retain more Na+ and manifest a greater rise in arterial pressure than salt-resistant patients. Because there is limited information regarding the role of nitric oxide (NO) in salt-sensitivity we examined the effects of L-arginine (500 mg/kg, i.v. for 30 min) on mean arterial pressure and renal haemodynamics in 21 hypertensive and five normotensive African-Americans. At the end of L-arginine infusion mean arterial pressure fell more in salt-sensitive (-11.5 +/- 2.5) than in salt-resistant (-3.7 +/- 1.5 mm Hg) and control subjects (-3.2 +/- 3.8 mm Hg). At the end of L-arginine infusion effective renal plasma flow (ERPF) increased more (P < 0.05) in controls (+108 +/- 13.9 ml/min/1.73 m2) than in salt-resistant (+55 +/- 16.0 ml/min/1.73 m2) and salt-sensitive patients (+22 +/- 21.5 ml/min/1.73 m2). This study has shown that salt-sensitive African-Americans manifest different systemic and renal haemodynamic responses to L-arginine than salt-resistant patients and controls. The fall in mean blood pressure following L-arginine was greater in salt-sensitive than in salt-resistant patients and controls, whereas the increase in ERPF was reduced in salt-sensitive compared to salt-resistant and normal subjects. The data are in keeping with the notion that a defect in NO production may participate to the genesis of blood pressure sensitivity to salt.

Microalbuminuria in essential hypertension

Some patients with essential hypertension manifest increased urinary albumin excretion (UAE). Hypertensive patients with microalbuminuria manifest abnormal circadian variation of blood pressure, increased serum levels of LDL-cholesterol and lipoprotein(a), a greater rise of serum insulin in response to an oral glucose tolerance test, and greater thickness of the carotid artery than patients without microalbuminuria. A 7 year follow-up of 141 hypertensive patients, 54 with microalbuminuria and 87 without microalbuminuria, we observed 12 cardiovascular events in patients with microalbuminuria and only 2 events in the patients with normal urine albumin excretion (P < 0.0002). Creatinine clearance decreased more in patients with microalbuminuria than in those with normal UAE. In conclusion, hypertensive individuals with microalbuminuria manifest a greater incidence of cardiovascular events and more decline in renal function than patients with normal UAE. We propose that measurements of UAE may be a useful marker for cardiovascular risk in patients with essential hypertension.

Neurogenic factors and hypertension in chronic renal failure

The association between hypertension and chronic renal disease is well recognized. Various factors may play a role in the pathogenesis of hypertension in chronic renal failure. Those include sodium retention and volume expansion, and increased activity of vasoconstrictors, such as the renin-angiotensin system. More recently, increased activity of the sympathetic nervous system has emerged as a leading factor in the pathogenesis of hypertension in these patients. We have used the model of 5/6 nephrectomized rats to study the role of the sympathetic nervous system in the pathogenesis of this form of hypertension. We have shown greater norepinephrine turnover rate in the posterior hypothalamic nuclei and locus coeruleus of CRF than control rats. Dorsal rhizotomy prevented the rise in blood pressure and the increase in NE turnover rate in the posterior hypothalamus and the locus coeruleus. An acute injury to the kidney produced by intrarenal injection of phenol, causes an immediate rise in blood pressure and in NE secretion from the posterior hypothalamus, that can be prevented by renal denervation. Dorsal rhizotomy prevented the development of hypertension in rats with chronic renal failure. The studies suggest that afferent impulses from the kidney to central integrative structures in the brain may be responsible for the rise in blood pressure in chronic renal failure.

Renal afferent impulses, the posterior hypothalamus, and hypertension in rats with chronic renal failure

Hypertension in 5/6 nephrectomized (CRF) rats is partly related to increased activity of the sympathetic nervous system. We have previously shown a greater norepinephrine turnover rate in the posterior hypothalamic nuclei and locus coeruleus of CRF than control rats. Dorsal rhizotomy prevented the rise in blood pressure and the increase in NE turnover rate in the posterior hypothalamus and the locus coeruleus. The studies suggest that afferent impulses from the kidney to central integrative structures in the brain may be responsible for hypertension in CRF rats. To further evaluate the role of renal afferent nerves in the regulation of blood pressure, and whether renal afferent pathways integrate with the posterior hypothalamus, we studied the effects of an intrarenal injection of 50 microliters of 10% phenol on blood pressure and NE secretion from the posterior hypothalamus of Sprague-Dawley rats. Mean arterial pressure increased from 89 +/- 4.0 to 114 +/- 4.3 mm Hg in rats which received intrarenal injection of phenol, but it did not change in rats that received vehicle (95 +/- 4.3 and 89 +/- 3.6 mm Hg, respectively). Renal denervation totally prevented the increase in blood pressure caused by intrarenal injection of phenol. The secretion of NE from the posterior hypothalamus increased from 139 +/- 4.8 to 250 +/- 9.9 pg/ml (P < 0.01) in rats that received intrarenal phenol, but it did not change in rats which received vehicle or in those with renal denervation. In CRF rats NE secretion from the posterior hypothalamus was greater than in control and CRF rats subjected to dorsal rhizotomy. These studies show that afferent impulses from an injured kidney increase NE secretion from the posterior hypothalamus and raise blood pressure. NE secretion is higher in the posterior hypothalamus of CRF than control rats. The posterior hypothalamus appears to be an important integrative structure of the sympathetic regulation of blood pressure.

Nitric oxide (NO) modulates the neurogenic control of blood pressure in rats with chronic renal failure (CRF)

Increased sympathetic nervous system (SNS) activity plays a role in the genesis of hypertension in rats with chronic renal failure (CRF). Because nitric oxide (NO) modulates the activity of the SNS, a deficit of NO synthesis could be responsible for the increased SNS activity in these animals. In the present study, we evaluated the effects of L-arginine and L-NAME on blood pressure and SNS activity-in Sprague Dawley 5/6 nephrectomized or sham-operated rats. SNS activity was determined by measuring norepinephrine turnover rate in several brain nuclei involved in the regulation of blood pressure. In the same brain nuclei, we measured NO content and nitric oxide synthase (NOS) gene expression by semiquantitative measurements of NOS mRNA reverse transcription polymerase chain reaction. In CRF rats, norepinephrine turnover rate was increased in the posterior hypothalamic nuclei, locus coeruleus, paraventricular nuclei, and the rostral ventral medulla, whereas NOS mRNA gene expression and NO2/NO3 content were increased in all brain nuclei tested. L-NAME increased blood pressure and NE turnover rate in several brain nuclei of both control and 5/6 nephrectomized rats. In CRF rats, a significant relationship was present between the percent increment in NOS mRNA gene expression related to the renal failure, and the percent increase in norepinephrine turnover rate caused by L-NAME. This suggests that endogenous NO may partially inhibit the activity of the SNS in brain nuclei involved in the neurogenic regulation of blood pressure, and this inhibition is enhanced in CRF rats. In summary, the increase in SNS activity in the posterior hypothalamic nuclei and in the locus coeruleus of CRF rats is partially mitigated by increased local expression of NOS m-RNA.

Salt intake and plasma atrial natriuretic peptide and nitric oxide in hypertension

In response to a high salt intake, salt-sensitive hypertensive individuals retain more sodium and manifest a rise in blood pressure greater than that in salt-resistant individuals. In this study, we tested whether salt sensitivity might be related at least in part to reduced secretion of atrial natriuretic peptide (ANP) or to abnormal nitric oxide production. We measured plasma ANP and NO2+NO3 in 7 normotensive individuals and 13 salt-sensitive and 14 salt-resistant blacks with essential hypertension under conditions of low (10 mEq/d) and high (250 mEq/d) salt intake. To evaluate possible racial differences in ANP secretion, we also measured plasma ANP in 6 salt-sensitive and 8 salt-resistant hypertensive whites during low and high salt intakes. Under low salt conditions, plasma ANP levels were not different in normotensive control subjects and salt-sensitive and salt-resistant hypertensive blacks. During high salt intake, plasma ANP levels did not change in control subjects and salt-resistant patients but decreased in salt-sensitive patients. ANP levels after high salt diet were lower (P < .01) in salt-sensitive than salt-resistant blacks. In hypertensive whites, high salt intake caused no significant change in plasma ANP. Under low salt conditions, plasma NO2+NO3 levels were higher (P < .05) in salt-sensitive (189 +/- 7.9 mumol/L) and salt-resistant (195 +/- 13.5 mumol/L) black patients than in control subjects (108 +/- 9.7 mumol/L). During high salt intake, plasma NO2+NO3 decreased significantly (P < .01) in both salt-sensitive (150 +/- 7.0 mumol/L) and salt-resistant (142 +/- 9.0 mumol/L) patients. These studies show that under conditions of high salt intake, salt-sensitive hypertensive blacks manifest a paradoxical decrease in ANP secretion. This abnormality may play a role in the reduced ability of these individuals to excrete a sodium load and in the sodium-induced rise in blood pressure. This study does not support the hypothesis that salt sensitivity depends on a deficit of nitric oxide production, but it suggests that high salt intake may alter the endothelium-dependent adaptation of peripheral resistance vessels.

The kidney in the hypertensive black

Evidence suggests that the incidence of end-stage renal disease due to essential hypertension is five to six times more frequent in black than in white patients. The reason for this greater susceptibility is not clear. Several possibilities have been proposed, including socioeconomic factors, compliance with therapy, renal hemodynamic differences and anatomic differences. In this review, we propose that the greater propensity of black hypertensives to develop renal failure as a consequence of hypertension may be due to abnormal hemodynamic adaptation of the renal circulation to a rise in blood pressure caused by high dietary sodium intake. This would make the renal circulation of hypertensive blacks more susceptible to injury.

Disparate prognosis of thrombotic microangiopathy in HIV-infected patients with and without AIDS

Thrombotic microangiopathy (TMA) is more common in HIV-infected individuals than in the normal population. In idiopathic TMA, plasmapheresis with or without prednisone decreases the mortality rate from almost 100 to 10%. Patients with HIV-associated TMA, who do not have AIDS, have a similar favorable outcome when treated with plasmapheresis. However, all 12 patients previously reported with AIDS-associated TMA have died. We report another patient with AIDS-associated TMA, who had a fulminant hospital course and died despite plasmapheresis. None of the reported AIDS-associated TMA patients had evidence of opportunistic infections, sepsis or disseminated malignancies at the time of their death. Since many infections and malignancies can be associated with TMA, it is possible that TMA can be an association of the terminal illness rather than an independent cause of death in AIDS patients. To examine this possibility, we reviewed the charts of all the patients who were hospitalized and died of AIDS at our medical centers from 1987 to 1994. Of the 214 patients reviewed, 15 patients (7%) had evidence of TMA at the time of their death. Seven of the 15 patients (47%) had no direct cause of death other than TMA. The remaining 8 patients had evidence of sepsis and other overwhelming infections. In conclusion, TMA is common in AIDS patients. While HIV-associated TMA has a good prognosis similar to that of idiopathic TMA, AIDS-associated TMA has a grave prognosis. The etiology of the higher mortality in AIDS-associated TMA as compared to HIV-associated TMA remains unclear.

Clustering of cardiovascular risk factors in salt-sensitive patients with essential hypertension: role of insulin

Hyperinsulinemia, insulin resistance, or both have been described in a proportion of patients with essential hypertension, and also are considered a risk for atherosclerotic cardiovascular disease. In this study, we have examined whether salt sensitivity and hyperinsulinemia are associated in patients with essential hypertension. We have measured blood insulin and glucose response to an acute oral glucose load in a group of hypertensive patients, classified according to their salt sensitivity. To determine salt sensitivity, patients received a diet containing a low (20 mEq/day) Na+ intake for 1 week followed by a high (250 mEq/day) Na+ intake for 1 week more. Twenty-nine patients were classified as salt sensitive, and 23 as salt resistant. Baseline plasma glucose and insulin were not different between salt-sensitive and salt-resistant patients. Following an oral glucose load, the area-under-the curve of glucose was greater (P < .05) in salt-sensitive than in salt-resistant hypertensive patients (900 +/- 26.4 and 810 +/- 29.1 mmol/L x 2 h, respectively). The area-under-the curve of insulin was greater (P < .01) in salt-sensitive (52,664 +/- 3,666 pmol/L x 2 h) than in salt-resistant patients (37,977 +/- 3,300 pmol/L x 2 h). A direct correlation was present between insulin area-under-the curve and salt sensitivity (r = 0.26), but did not reach statistical significance (P < .06). Salt-sensitive patients manifested increased serum levels of total cholesterol, LDL-cholesterol and increased urinary albumin excretion when compared with salt-resistant patients. In conclusion, these studies have demonstrated that in response to an oral glucose load, salt-sensitive patients with essential hypertension manifest increased insulin secretion. The studies have confirmed the presence of increased urinary albumin excretion and serum levels of atherogenic lipoproteins in salt-sensitive compared with salt-resistant patients. In salt-sensitive hypertensive patients, hyperinsulinemia, hyperlipidemia and microalbuminuria form a cluster with possible atherogenic potential. Salt sensitivity can be a marker for increased cardiovascular risk in patients with essential hypertension.

Renal afferent denervation prevents the progression of renal disease in the renal ablation model of chronic renal failure in the rat

Rats with 5/6 nephrectomy develop hypertension and progressive deterioration in renal function. Several mechanisms may contribute to hypertension and to progressive renal disease in these rats. We have shown that increased activity of the sympathetic nervous system may contribute to hypertension in rats we chronic renal failure. However, the role of the sympathetic nervous system activity in the progression of renal disease has not been investigated. We have evaluated whether neurogenic factors contribute to the progression of renal disease in the renal ablation model of chronic renal failure in the rat. Sprague-Dawley rats underwent 5/6 nephrectomy and dorsal rhizotomy or sham rhizotomy (CRF). Age-matched normal rats were used as controls. Six weeks after surgery, rats with chronic renal failure and dorsal rhizotomy had lower blood pressure and serum creatinine than rats with sham rhizotomy. In addition, kidneys from rats with 5/6 nephrectomy and rhizotomy manifested less severe glomerulosclerosis than kidneys from rats without dorsal rhizotomy. These studies have demonstrated in rats with renal ablation. Although normalization of blood pressure may definitely play a role, the data raise the possibility that neurogenic impulses to the kidneys may contribute to the progression of renal disease.

Increased thickness of the carotid artery in patients with essential hypertension and microalbuminuria

In patients with essential hypertension, the presence of microalbuminuria carries an increased risk for cardiovascular morbidity and mortality. The mechanisms responsible for this association are not clear. Microalbuminuria could signal the presence of generalised atherosclerosis. To determine the extent of atherosclerosis, we measured by B-mode ultrasound imaging the thickness of the intima and media layers of the carotid artery in 30 hypertensive patients with microalbuminuria, 30 patients without microalbuminuria and 30 normotensive healthy subjects. In hypertensive patients with microalbuminuria, urinary albumin excretion (55 +/- 4.7 mg/24 h) was greater (P < 0.01) than in patients without microalbuminuria (12 +/- 0.9 mg/24 h) and in healthy subjects (7.1 +/- 0.52 mg/24 h). In hypertensive patients with microalbuminuria, the thickness of the carotid artery (0.78 +/- 0.02 mm) was greater (P < 0.01) than in patients without microalbuminuria (0.69 +/- 0.01 mm) and in healthy subjects (0.64 +/- 0.02 mm). In hypertensive patients with microalbuminuria, the mean insulin area-under-the curve (59,703 +/- 4,874 pmol/L x 2 h) and glucose area-under-the curve (928 +/- 40.0 mmol/L x 2 h) were significantly greater (P < 0.005) than in patients without microalbuminuria (38,774 +/- 4,104 pmol/L x 2 h and 803 +/- 34.7 mmol/L x 2 h, respectively), and in normotensive healthy subjects (27,557 +/- 2563 pmol/L x 2 h and 837 +/- 31.2 mmol/L x 2 h, respectively). Serum levels of total cholesterol, triglycerides and lipoprotein(a) were higher in hypertensives with than in those without microalbuminuria. The thickness of the carotid artery was significantly correlated with microalbuminuria, blood pressure, cholesterol, serum triglycerides and insulin area-under-the curve. In conclusion, this study shows that hypertensive patients with microalbuminuria have an increased thickness of the carotid intima and media layers suggesting a greater degree of atherosclerosis. Measurements of urinary albumin excretion may be important in the evaluation of patients with essential hypertension.

Renal afferent denervation prevents hypertension in rats with chronic renal failure

Increased activity of the sympathetic nervous system has been described in chronic renal failure, but its role in the genesis and maintenance of hypertension associated with this condition has not been established. The kidney has an intense network of chemoreceptors and baroreceptors that send impulses to the brain. To what extent activation of these receptors by the scarred kidney or the uremic milieu may contribute to this model of hypertension is unknown. In the present study, we evaluated the effect of bilateral dorsal rhizotomy on the development of hypertension and neuroadrenergic activity in the anterior, lateral, and posterior hypothalamic nuclei, in the locus ceruleus, and in the nucleus tractus solitarius of Sprague-Dawley rats that underwent 5/6 nephrectomy or were sham operated. Neuroadrenergic activity was determined by calculating norepinephrine turnover rate after inhibition of norepinephrine synthesis with alpha-methyl-DL-p-tyrosine methyl ester hydrochloride. The endogenous norepinephrine concentration was significantly greater in the posterior and lateral hypothalamic nuclei and the locus ceruleus, but not in the nucleus tractus solitarius, and the anterior hypothalamic nuclei of uremic rats compared with control rats. In rats with chronic renal failure and sham rhizotomy, the turnover rate of norepinephrine in the posterior (15.3 +/- 1.61 nmol.g-1.h-1) and lateral hypothalamic nuclei (11.7 +/- 2.12 nmol.g-1.h-1) and in the locus ceruleus (26.6 +/- 2.42 nmol.g-1.h-1) was significantly faster (P < .01) than in rats with renal failure and dorsal rhizotomy (4.1 +/- 0.51, 4.7 +/- 0.77, and 5.1 +/- 1.13 nmol.g-1.h-1, respectively) or control animals with or without rhizotomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of long-term therapy with captopril on proteinuria and renal function in patients with non-insulin-dependent diabetes and with non-diabetic renal diseases

Several studies have shown that long-term therapy with angiotensin-converting enzyme inhibitors may reduce urinary protein excretion and decrease the rate of progression of renal disease in patients with insulin-dependent diabetes mellitus more effectively than conventional antihypertensive drugs. Only few studies, however, have been performed in patients with non-insulin-dependent diabetes mellitus (NIDDM). To compare the effects of captopril with more conventional drugs on proteinuria and progression of renal disease, we conducted a prospective, 18-month study in 42 proteinuric (> 500 mg/day) NIDDM and, for comparison, in 31 nondiabetic patients with a variety of renal diseases (NDRD). Twenty-four NIDDM patients were treated with captopril and 18 with conventional drugs. Eighteen NDRD patients received captopril, and 13 received conventional drugs. Baseline proteinuria and glomerular filtration rate (GFR) were not different among groups. The blood pressure decreased equally in all group of patients, irrespective of whether they received captopril or conventional drugs. Urinary protein excretion, however, decreased significantly only in NIDDM and NDRD patients treated with captopril. The GFR decreased only in patients treated with conventional drugs, but not in those treated with captopril. The rate of decline in GFR in NIDDM patients treated with captopril was significantly lower than in patients treated with conventional drugs. However, in NDRD patients treated with captopril, the rate of decline in GFR was not different from that in patients treated with conventional drugs. The reduction of urinary protein excretion was poorly correlated with changes in blood pressure or with changes in renal function and renal hemodynamics. Serum potassium increased significantly in patients treated with captopril.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurogenic factors in hypertension: therapeutic implications

This manuscript reviews the evidence supporting a role for neurogenic factors in the pathophysiology of essential hypertension. The available evidence in human subjects is largely indirect and suggests a role for the sympathetic nervous system primarily in younger patients with borderline hypertension. In predisposed subjects, environmental factors, such as stress and high dietary salt intake, may activate the sympathetic nervous system and cause hypertension. With advancing age, vascular structural changes may contribute to the maintenance of hypertension despite a seemingly normal sympathetic nerve activity. The evidence supporting a role for neurogenic factors in the genesis of hypertension in patients with chronic renal failure has also been reviewed. Afferent stimuli from the scarred or diseased kidneys into the central nervous system may activate the sympathetic nervous system and contribute to the genesis of hypertension in patients with chronic renal failure. These observations may explain the efficacy of antiadrenergic agents in the management of hypertension in these patients.

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)

Altered norepinephrine turnover in the brown fat of rats with chronic renal failure

Disturbances of the sympathetic nervous system (SNS) have been described in chronic renal failure, but their role in the metabolic derangements of uremia has not been well established. In these studies, SNS activity has been measured in the ventromedial hypothalamic (VMH) nuclei and in the intercostal brown adipose tissue (IBAT) of Sprague Dawley 5/6 nephrectomized or sham-operated rats. SNS activity was determined by calculating the norepinephrine (NE) turnover rate (in picograms per milligram per hour) 3, 6, and 12 h after the inhibition of NE synthesis with L-methyltyrosine. The endogenous NE concentration was significantly (P < 0.01) higher in the VMH (14,567 +/- 1,130 pg/mg wet wt) and IBAT (17,902 +/- 2,308 pg/mg wet wt) of uremic than control rats (9,600 +/- 1,110 and 5,752 +/- 320 pg/mg wet wt, respectively). The turnover rates of NE in the VMH (582 +/- 146 pg/mg per hour) and in the IBAT (1,432 +/- 179 pg/mg/hr) of uremic rats were significantly faster (P < 0.01) than in control rats (192 +/- 96 and 173 +/- 58 pg/mg per hour, respectively). These studies demonstrate a significant increase in NE turnover in the VMH nuclei and IBAT of uremic rats. It is suggested that increased efferent sympathetic nerve discharge from the VMH to the IBAT may play a role in the pathogenesis of malnutrition in uremia.

Altered norepinephrine turnover in the brain of rats with chronic renal failure

Disturbances of the sympathetic nervous system have been described in chronic renal failure, but their role in the genesis and maintenance of hypertension frequently associated with this condition has not been established. The neuroadrenergic activity in brain nuclei involved in the regulation of blood pressure in uremic animals has also not been previously evaluated. In these studies, the neuroadrenergic activity was measured in the anterior, lateral, and posterior hypothalamic nuclei, in the locus coeruleus, and in the nucleus tractus solitarius of Sprague Dawley rats 5/6 nephrectomized or sham operated 4 wk before the experiments. Neuroadrenergic activity was determined by calculating norepinephrine (NE) turnover rate (in picograms per milligram per hour), 3, 6 and 12 h after inhibition of NE synthesis with L-methyltyrosine. The endogenous NE concentration was significantly greater in the posterior hypothalamic nuclei (21,501 +/- 1,777 pg/mg wet wt) and in the locus coeruleus (16,152 +/- 1,114 pg/mg wet tissue) of uremic compared with control rats (12,213 +/- 1,404 and 7,991 +/- 622 pg/mg wet wt, respectively). On the other hand, the endogenous NE content of the nucleus tractus solitarius and the anterior hypothalamic nuclei did not differ between uremic and control rats. The turnover rate of NE in the posterior hypothalamic nuclei of uremic rats (2150 +/- 430 pg/mg per hour) was significantly faster (P < 0.05) than in control rats (977 +/- 244 pg/mg per hour). The turnover rate of NE in the locus coeruleus of uremic rats (2,584 +/- 323 pg/mg per hour) was also significantly faster than in control animals (400 +/- 140 pg/mg per hour; P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Salt sensitivity in hypertension. Renal and cardiovascular implications

The mechanisms responsible for the increase in blood pressure response to high salt intake in salt-sensitive patients with essential hypertension are complex and only partially understood. A complex interaction between neuroendocrine factors and the kidney may underlie the propensity for such patients to retain salt and develop salt-dependent hypertension. The possible role of vasodilator and natriuretic agents, such as the prostaglandins, endothelium-derived relaxing factor, atrial natriuretic factor, and kinin-kallikrein system, requires further investigation. An association between salt sensitivity and a greater propensity to develop renal failure has been described in certain groups of hypertensive patients, such as blacks, the elderly, and those with diabetes mellitus. Salt-sensitive patients with essential hypertension manifest a deranged renal hemodynamic adaptation to a high dietary salt intake. During a low salt diet, salt-sensitive and salt-resistant patients have similar mean arterial pressure, glomerular filtration rate, effective renal plasma flow, and filtration fraction. On the other hand, during a high salt intake glomerular filtration rate does not change in either group, and effective renal blood flow increases in salt-resistant but decreases in salt-sensitive patients; filtration fraction and glomerular capillary pressure decrease in salt-resistant but increase in salt-sensitive patients. Salt-sensitive patients are also more likely than salt-resistant patients to manifest left ventricular hypertrophy, microalbuminuria, and metabolic abnormalities that may predispose them to cardiovascular diseases. In conclusion, salt sensitivity in hypertension is associated with substantial renal, hemodynamic, and metabolic abnormalities that may enhance the risk of cardiovascular and renal morbidity.

Hypokalemic effects of intravenous infusion or nebulization of salbutamol in patients with chronic renal failure: comparative study

To examine and compare the efficacy and safety of different routes of administration of salbutamol in treating hyperkalemia, 15 patients with chronic renal failure (blood urea nitrogen > 80 mg/dL, serum creatinine > 8.0 mg/dL) were enrolled to sequentially receive either intravenous infusion (0.5 mg) or nebulization (10 mg) of salbutamol. Five of these patients (33.3%) did not respond to the intravenous salbutamol and were excluded from the study. Both treatments significantly decreased plasma potassium in 10 patients and the decrease was sustained for at least 3 hours. After infusion, the maximal reduction in plasma potassium levels was 0.92 +/- 0.10 mEq/L and occurred after 30 minutes. On the other hand, the maximal reduction in plasma potassium after nebulization (0.85 +/- 0.13 mEq/L) was similar to that after infusion, but it occurred after 90 minutes. Insulin and blood glucose increased, whereas blood pH, PCO2, sodium, osmolality, and blood pressure did not change after either treatment. Heart rate increased significantly after both treatments, but less after nebulization than after infusion. It is concluded that both infusion and nebulization are simple, effective, and safe therapeutic modalities for the treatment of hyperkalemia in patients with chronic renal failure. Infusion should be used in patients requiring a rapid decrease in plasma potassium; nebulization, on the other hand, should be used in patients with coronary artery diseases.

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.

Diurnal variations of blood pressure and microalbuminuria in essential hypertension

Microalbuminuria has been shown in approximately 40% of patients with essential hypertension. Previous studies have failed to demonstrate any consistent relationship between microalbuminuria and levels of office blood pressure. Because average ambulatory blood pressure correlates with incidence of cardiovascular morbidity and mortality better than office blood pressure, we have studied whether levels of urinary albumin excretion correlate with average diurnal, nocturnal, or 24-h blood pressure better than with office blood pressure. Sixty-three patients with essential hypertension and 21 healthy volunteers were included in the study. Twenty-four hypertensive patients failed to show the normal nighttime fall in blood pressure of at least 10/5 mm Hg and were defined as "nondippers"; the remaining were defined as "dippers." Office blood pressure was not different between dippers and nondippers. However, nighttime systolic and diastolic blood pressures were significantly greater in nondippers than in dippers. The median urinary albumin excretion in nondippers (42 mg/24 h) was significantly greater (P < .001) than in dippers (17.5 mg/24 h), and in normal subjects (8.6 mg/24 h). A significant correlation was present between nighttime systolic and diastolic blood pressure and urinary albumin excretion (UAE) and between 24-h systolic blood pressure and UAE in all hypertensive patients; in addition, a significant correlation was present between 24-h diastolic and nighttime diastolic blood pressure and UAE in nondippers. The increased amount of UAE in nondipper hypertensive patients suggests the presence of greater renal damage than in dippers.

Tuberculosis of the spine (Pott's disease) in patients with end-stage renal disease

Extrapulmonary tuberculosis is more common in end-stage renal disease than in normal subjects, and it frequently poses both diagnostic and therapeutic challenges. We describe 2 dialysis patients with tuberculosis of the spine (Pott's disease). The 1st patient presented with back and left hip pain, low-grade fever, left-quadriceps weakness, hypoesthesia of the left thigh, and hypoactive left-knee jerk. X-rays of the spine showed only osteophytes. Magnetic resonance imaging showed increased signal intensity of L3 with focal expansion into the spinal canal. A computerized tomography guided biopsy revealed granulomas, and Ziehl-Neelsen stain was positive. Therapy with rifampin, isoniazid, ethambutol, and pyrazinamide caused peripheral neuropathy and optic neuritis. The 2nd patient developed bilateral proximal thigh pain and weakness that progressed to paraplegia. Magnetic resonance imaging showed destructive lesion of L3-5, involving both psoas muscles, prevertebral space, and neural foramina. Ziehl-Neelsen stain of the biopsy specimen was negative, but culture was positive for Mycobacterium tuberculosis. Paraplegia improved only partially after 1 year of therapy. Pott's disease should be suspected in end-stage renal disease patients with back pain and/or neuromuscular complaints, particularly in those who immigrated from Asian and Latin-American countries. Treatment of tuberculosis in dialysis patients may cause significant morbidity.