Hypertension in an experimental model of systemic lupus erythematosus occurs independently of the renal nerves.

Systemic lupus erythematosus (SLE) is a chronic inflammatory disorder with prevalent hypertension and renal injury. In this study, we tested whether the renal nerves contribute to the development of hypertension in an established mouse model of SLE (NZBWF1). Female SLE and control (NZW/LacJ) mice were subjected to either bilateral renal denervation or a sham procedure at 32 wk of age. Two weeks later, blood pressure was assessed in conscious mice using carotid artery catheters. Blood pressure was higher in SLE mice compared with controls, as previously reported; however, blood pressure was not altered in the denervated SLE or control mice. The development of albuminuria was markedly blunted in denervated SLE mice; however, glomerulosclerosis was increased. Renal denervation reduced renal cortical expression of monocyte-chemoattractant protein in SLE mice but did not significantly alter renal monocyte/macrophage infiltration. Renal cortical TNF-α expression was also increased in sham SLE mice, but this was not impacted by denervation. This study suggests that the renal nerves do not have a significant role in the pathogenesis of hypertension, but have a complex effect on the associated renal inflammation and renal injury.

Pulmonary emboli from therapeutic sodium hyaluronate.

A patient presented with shortness of breath and pleuritic pain shortly after bilateral knee synovial injections with sodium hyaluronate (HA). He was discharged after a brief hospitalization without a diagnosis when no Doppler or radiologic evidence of deep vein thrombosis or pulmonary emboli was found. Radiologic studies found patchy ground glass opacities that were predominantly peripheral in disposition, with prominent septal lines in the lungs; a subsequent pulmonary function test showed a reduced diffusing capacity of the lung for carbon monoxide (D(LCO)). These results prompted a lung biopsy that revealed multiple emboli composed of HA and fibrin in medium size pulmonary arteries, enlarged lymphatic vessels, and a bone marrow embolus. This is the first report of HA emboli following therapeutic HA injections and demonstrates that pulmonary function tests can be used to infer the reduction in pulmonary vascular area consequent to pulmonary emboli, and so can contribute to the detection of pulmonary emboli in unusual presentations.

Sustained suppression of sympathetic activity and arterial pressure during chronic activation of the carotid baroreflex.

Following sinoaortic denervation, which eliminates arterial baroreceptor input into the brain, there are slowly developing adaptations that abolish initial sympathetic activation and hypertension. In comparison, electrical stimulation of the carotid sinus for 1 wk produces sustained reductions in sympathetic activity and arterial pressure. However, whether compensations occur subsequently to diminish these responses is unclear. Therefore, we determined whether there are important central and/or peripheral adaptations that diminish the sympathoinhibitory and blood pressure-lowering effects of more sustained carotid sinus stimulation. To this end, we measured whole body plasma norepinephrine spillover and alpha(1)-adrenergic vascular reactivity in six dogs over a 3-wk period of baroreflex activation. During the first week of baroreflex activation, there was an approximately 45% decrease in plasma norepinephrine spillover, along with reductions in mean arterial pressure and heart rate of approximately 20 mmHg and 15 beats/min, respectively; additionally, plasma renin activity did not increase. Most importantly, these responses during week 1 were largely sustained throughout the 3 wk of baroreflex activation. Acute pressor responses to alpha-adrenergic stimulation during ganglionic blockade were similar throughout the study, indicating no compensatory increases in adrenergic vascular reactivity. These findings indicate that the sympathoinhibition and lowering of blood pressure and heart rate induced by chronic activation of the carotid baroreflex are not diminished by adaptations in the brain and peripheral circulation. Furthermore, by providing evidence that baroreflexes have long-term effects on sympathetic activity and arterial pressure, they present a perspective that is opposite from studies of sinoaortic denervation.

N-Acetylcysteine improves renal dysfunction, ameliorates kidney damage and decreases blood pressure in salt-sensitive hypertension.

BACKGROUND: Salt-sensitive hypertension in humans and experimental animals causes progressive increases in renal damage and dysfunction. The Dahl salt-sensitive (S) rat closely mimics human salt-sensitive hypertension. AIM: Our goal was to test the hypothesis that enhancing the glutathione system with dietary N-acetylcysteine administration in Dahl S rats on a high sodium intake for 5 weeks will attenuate the increases in arterial pressure, the decreases in renal hemodynamics and the increases in renal damage that normally occur in S rats on high sodium. METHODS: Forty-four 7- to 8-week-old Dahl S/Rapp strain rats were maintained on a high sodium (8%), high sodium + N-acetylcysteine (4 g/kg per day), or low sodium (0.3%) diet for 5 weeks. Rats had arterial and venous catheters implanted at day 21. RESULTS: By day 35 in the high-sodium rats, N-acetylcysteine treatment significantly increased the renal reduced-to-oxidized glutathione ratio, glomerular filtration rate, and renal plasma flow, and decreased renal cortical and medullary O2 release, urinary protein excretion, renal tubulointerstitial damage and glomerular necrosis. At this time, mean arterial pressure increased to 183 +/- 1 mmHg, and N-acetylcysteine reduced this arterial pressure to 121 +/- 4 mmHg. By day 35 in S high-sodium rats, N-acetylcysteine had caused a 91% decrease in glomerular necrosis and an 83% decrease in tubulointerstitial damage. CONCLUSIONS: In Dahl S rats on high sodium intake, arterial pressure increases significantly and renal injury is pronounced. Treatment with N-acetylcysteine enhances the renal glutathione system, improves renal dysfunction and markedly decreases arterial pressure and renal injury in Dahl salt-sensitive hypertension.

Cigarette smoke-induced airway inflammation as sampled by the expired breath condensate.

Airways exposed to smoke respond with inflammatory processes. The airway inflammation generally present in smokers causes persistent cough and phlegm production, reactive airway disease, and tissue infiltration by inflammatory cells. Although the short-term response may be protective, long-term pathological consequences include swelling of the airway epithelium, mucus hypersecretion, and increased airway reactivity characteristic of chronic bronchitis and chronic obstructive lung disease and the tissue destruction characteristic of emphysema. The natural history of these diseases is poorly understood, because human airway tissue is available for study only at autopsy, from surgical specimens, or from procedures such as bronchoscopy or thoracotomy. A noninvasive method of monitoring the inflammation is by analyzing expired breath condensate, which contains a diluted sample of airway surface liquid. The study of expired breath condensate may offer a more practical approach to sampling airway chemistry and make it possible to study the detailed inflammatory response to airborne particulates.

Prolonged activation of the baroreflex decreases arterial pressure even during chronic adrenergic blockade.

Previous studies suggest that prolonged electric activation of the baroreflex may reduce arterial pressure more than chronic blockade of alpha(1)- and beta(1,2)-adrenergic receptors. To determine whether central inhibition of sympathetic outflow has appreciable effects to chronically reduce arterial pressure by actions distinct from well-established mechanisms, we hypothesized that chronic baroreflex activation would lower arterial pressure substantially even during complete alpha(1)- and beta(1,2)-adrenergic receptor blockade. This hypothesis was tested in 6 dogs during adrenergic blockade (AB; 18 days) with and without electric activation of the carotid baroreflex (7 days). During chronic AB alone, there was a sustained decrease in the mean arterial pressure of 21+/-2 mm Hg (control: 95+/-4 mm Hg) and an approximately 3-fold increase in plasma norepinephrine concentration (control: 138+/-6 pg/mL), likely attributed to baroreceptor unloading. In comparison, during AB plus prolonged baroreflex activation, plasma norepinephrine concentration decreased to control levels, and mean arterial pressure fell an additional 10+/-1 mm Hg. Because of differences in plasma norepinephrine concentration, we also tested the acute blood pressure-lowering effects of MK-467, a peripherally acting alpha(2)-antagonist. After administration of MK-467, there was a significantly greater fall in arterial pressure during AB (15+/-3 mm Hg) than during AB plus prolonged baroreflex activation (7+/-3 mm Hg). These findings suggest that reflex-induced increases in sympathetic activity attenuate reductions in arterial pressure during chronic AB and that inhibition of central sympathetic outflow by prolonged baroreflex activation lowers arterial pressure further by previously undefined mechanisms, possibly by diminishing attendant activation of postjunctional alpha(2)-adrenergic receptors.

Prolonged activation of the baroreflex abolishes obesity-induced hypertension.

Prolonged electrical activation of the carotid baroreflex produces sustained reductions in sympathetic activity and arterial pressure in normotensive dogs. The main goal of this study was to assess the influence of prolonged baroreflex activation on arterial pressure and neurohormonal responses in 6 dogs with obesity-induced hypertension. After control measurements, the diet was supplemented with cooked beef fat for 6 weeks, whereas sodium intake was held constant. After 4 weeks of the high-fat diet, there were increments in body weight from 25.8+/-0.7 to 38.6+/-1.0 kg, mean arterial pressure from 97+/-2 to 110+/-3 mm Hg, heart rate from 67+/-3 to 91+/-4 bpm, and plasma norepinephrine concentration from 141+/-35 to 280+/-52 pg/mL. Plasma glucose and insulin concentrations were elevated, but increases in plasma renin activity during the initial weeks of the high-fat diet were not sustained. During week 5, baroreflex activation resulted in sustained reductions in mean arterial pressure, heart rate, and plasma norepinephrine concentration; at the end of week 5, these values were 87+/-2 mm Hg, 77+/-4 bpm, and 166+/-45 pg/mL, respectively. These suppressed values returned to week 4 levels during a 7-day recovery period after baroreflex activation. There were no changes in plasma glucose or insulin concentrations, or plasma renin activity during prolonged baroreflex activation. These findings indicate that baroreflex activation can chronically suppress the sympathoexcitation associated with obesity and abolish the attendant hypertension while having no effect on hyperinsulinemia or hyperglycemia.

Early renal denervation prevents development of hypertension in growth-restricted offspring.

1. Low birth weight is associated with an increased risk for the development of hypertension. Our laboratory uses a model of reduced uterine perfusion in the pregnant rat that results in intrauterine growth-restricted (IUGR) offspring that develop hypertension at a prepubertal age. Although hypertension develops in both prepubertal male and female IUGR offspring, only male IUGR offspring remain hypertensive after puberty. We reported previously that bilateral renal denervation abolishes hypertension in adult male IUGR offspring, indicating an important role for the renal nerves in the maintenance of established IUGR-induced hypertension. We also reported that angiotensin-converting enzyme inhibition abolishes hypertension in adult male IUGR offspring. However, activation of the renin-angiotensin system does not occur in male IUGR offspring until after puberty, or after the development of established IUGR-induced hypertension. Therefore, the mechanisms involved in the development of IUGR-induced hypertension may differ from those involved in the maintenance of established IUGR-induced hypertension. Thus, the purpose of the present study was to determine whether the renal nerves play a causative role in the early development of IUGR-induced hypertension in prepubertal IUGR offspring. 2. Intrauterine growth-restricted and control offspring were subjected to either bilateral renal denervation or sham denervation, respectively, at 4 weeks of age. Mean arterial pressure (MAP) was determined at 6 weeks of age in conscious, chronically instrumented animals. Adequacy of renal denervation was verified by renal noradrenaline content. 3. Whereas renal denervation had no effect on MAP in control offspring (103 +/- 2 vs 102 +/- 3 mmHg for sham vs denervated, respectively), it reduced blood pressure in growth-restricted offspring (114 +/- 3 vs 104 +/- 1 mmHg for sham vs denervated, respectively; P < 0.01). Renal noradrenaline content was significantly reduced in denervated animals relative to sham operated rats. 4. Thus, the data indicate a role for the renal nerves in the aetiology of IUGR-induced hypertension and suggest that the renal nerves may participate in the early development of hypertension in IUGR offspring in addition to established hypertension observed in adult male IUGR offspring.

Renal denervation does not abolish sustained baroreflex-mediated reductions in arterial pressure.

Recent studies indicate that suppression of renal sympathetic nerve activity and attendant increments in renal excretory function are sustained baroreflex-mediated responses in hypertensive animals. Given the central role of the kidneys in long-term regulation of arterial pressure, we hypothesized that the chronic blood pressure-lowering effects of the baroreflex are critically dependent on intact renal innervation. This hypothesis was tested in 6 dogs by bilaterally activating the carotid baroreflex electrically for 7 days before and after bilateral renal denervation. Before renal denervation, control values for mean arterial pressure and plasma norepinephrine concentration were 95+/-2 mm Hg and 96+/-12 pg/mL, respectively. During day 1 of baroreflex activation, mean arterial pressure decreased 13+/-1 mm Hg, and there was modest sodium retention. Daily sodium balance was subsequently restored, but reductions in mean arterial pressure were sustained throughout the 7 days of baroreflex activation. Activation of the baroreflex was associated with sustained decreases in plasma norepinephrine concentration ( approximately 50%) and plasma renin activity (30% to 40%). All of the values returned to control levels during a 7-day recovery period. Two weeks after renal denervation, control values for mean arterial pressure, plasma norepinephrine concentration, plasma renin activity, and sodium excretion were comparable to those measured when the renal nerves were intact. Moreover, after renal denervation, all of the responses to activation of the baroreflex were similar to those observed before renal denervation. These findings demonstrate that the presence of the renal nerves is not an obligate requirement for achieving long-term reductions in arterial pressure during prolonged activation of the baroreflex.

Renal denervation abolishes hypertension in low-birth-weight offspring from pregnant rats with reduced uterine perfusion.

Low birth weight is a risk factor for the subsequent development of hypertension in humans. We previously reported that reduced uterine perfusion in the pregnant rat results in growth-restricted offspring predisposed to the development of hypertension. The purpose of this study was to determine whether the sympathetic nervous system plays a role in mediating hypertension in this model of low birth weight. Weight at birth was significantly decreased in male growth-restricted offspring (5.9+/-0.1 grams) as compared with male control offspring (6.5+/-0.2 grams; P<0.05). At 10 weeks of age, growth-restricted offspring and control offspring were randomly assigned to either an intact group (sham-denervated) or a group subjected to bilateral renal denervation. For sham-denervated offspring, mean arterial pressure was significantly elevated in growth-restricted offspring (145+/-4 mm Hg; n=7) as compared with control offspring (134+/-3 mm Hg; P<0.05; n=9) at 12 weeks of age. Bilateral renal denervation resulted in a marked reduction in arterial pressure in growth-restricted offspring (125+/-3 mm Hg; P<0.01; difference of 20 mm Hg versus sham growth-restricted; n=8) but no significant decrease in control offspring (127+/-3 mm Hg; difference of 7 mm Hg versus sham control; n=9). Adequacy of renal denervation was verified by >90% reduction in renal norepinephrine content. Therefore, these findings indicate the renal nerves play an important role in mediating hypertension in adult growth-restricted offspring.

Influence of prolonged baroreflex activation on arterial pressure in angiotensin hypertension.

Despite recent evidence indicating sustained activation of the baroreflex during chronic infusion of angiotensin II (Ang II), sinoaortic denervation does not exacerbate the severity of the hypertension. Therefore, to determine whether Ang II hypertension is relatively resistant to the blood pressure-lowering effects of the baroreflex, the carotid baroreflex was electrically activated bilaterally for 7 days in 5 dogs both in the presence and absence of a continuous infusion of Ang II (5 ng/kg per minute) producing high physiological plasma levels of the peptide. Under control conditions, basal values for mean arterial pressure (MAP) and plasma norepinephrine concentration (NE) were 93+/-1 mm Hg and 99+/-25 pg/mL, respectively. By day 7 of baroreflex activation, MAP and NE were reduced to 72+/-4 mm Hg (-21+/-3 mm Hg) and 56+/-15 pg/mL, respectively, but PRA was unchanged (control=0.41+/-0.06 ng ANG I/mL per hour). All values returned to basal levels by the end of a 7-day recovery period. After 7 days of Ang II infusion, MAP increased from 93+/-3 to 129+/-3 mm Hg, whereas NE fell from 117+/-15 to 86+/-23 pg/mL. During the next 7 days of baroreflex activation/Ang II infusion, further reductions in NE were not statistically significant, and on the final day of baroreflex activation, the reduction in MAP was only 5+/-1 mm Hg, compared with 21+/-3 mm Hg in the control normotensive state. These findings indicate that long-term baroreflex-mediated reductions in arterial pressure are markedly diminished, but not totally eliminated, in the presence of hypertension produced by chronic infusion of Ang II.

Sampling airway surface liquid: non-volatiles in the exhaled breath condensate.

Exhaled breath condensate (EBC) samples contain molecules that have no appreciable vapor pressure; such molecules likely derive from droplets of airway fluid. We analyzed EBC gathered from a total of 62 healthy volunteers in order to quantify the volume of airway liquid that was the source of the non-volatiles; saliva was analyzed as a reference secretion. EBC urea averaged 0.52 +/- 0.12 micromol/L (n = 18), an 8,600-fold dilution from predicted blood urea nitrogen levels. Protein averaged 2.3 +/- 0.3 microg/ml (n = 31), three orders of magnitude less than in saliva (1.4 +/- 0.1 mg/ml, n = 15). EBC ammonia was 6.6 +/- 0.6 mmol/L (1/15 that of saliva) and EBC ammonium ion was 0.90 +/- 0.19 micromol/L, concentrations that are incompatible with an 8,600-fold dilution from a biological source. Thus, urea-derived dilution factors may be used to interpret EBC non-volatile molecules, but not EBC volatiles.

The renal pelvis: machinery that concentrates urine in the papilla.

Two decades ago, Bodil Schmidt-Nielsen and Bruce Graves documented the rhythmic contractions of the renal pelvis in a remarkable video, visually demonstrating how peristaltic waves empty the papilla and how the subsequent elastic recoil draws water from the collecting duct and into the tethered-open ascending vasa recta. Thus a periodic hydrostatic gradient generates an axial osmotic gradient. This review recapitulates the video and offers a link to figures and scenes digitized from the original tape.

Is obesity a major cause of chronic kidney disease?

Excess weight gain is a major risk factor for essential hypertension and for end-stage renal disease (ESRD). Obesity raises blood pressure by increasing renal tubular sodium reabsorption, impairing pressure natriuresis, and causing volume expansion because of activation of the sympathetic nervous system and renin-angiotensin system and by physical compression of the kidneys, especially when visceral obesity is present. Obesity also causes renal vasodilation and glomerular hyperfiltration that initially serve as compensatory mechanisms to maintain sodium balance in the face of increased tubular reabsorption. In the long-term, however, these changes, along with the increased systemic arterial pressure, create a hemodynamic burden on the kidneys that causes glomerular injury. With prolonged obesity, there is increasing urinary protein excretion and gradual loss of nephron function that worsens with time and exacerbates hypertension. With the worsening of metabolic disturbances and the development of type II diabetes in some obese patients, kidney disease progresses much more rapidly. Weight reduction is an essential first step in the management of obesity, hypertension, and kidney disease. Special considerations for the obese patient, in addition to adequately controlling the blood pressure, include correction of the metabolic abnormalities and protection of the kidneys from further injury.