Enhanced cardiovascular pressor reactivity to norepinephrine in mild renal parenchymal disease

The impact of anticoagulation therapy on kidney function in patients with atrial fibrillation and chronic kidney disease

INTRODUCTION

Atrial fibrillation (AF) and chronic kidney disease (CKD) are closely related. These diseases share common risk factors and are associated with increased risk of thromboembolic events. Choosing the appropriate oral anticoagulant therapy (OAC) in patients with AF and CKD is challenging. Deterioration of renal function is common in patients with AF treated with OACs, although not all OACs affect the kidneys equally.

AREAS COVERED

In this review, we aim to summarize the current knowledge of the prevention of thromboembolic events in patients with AF and CKD, focusing on the impact of specific OAC agents on renal function.

EXPERT OPINION

Consideration of OAC use is mandatory in patients with AF and CKD who are at increased risk of stroke or systemic embolism. Available evidence suggests that the use of non-vitamin K antagonist oral anticoagulants (NOACs) is associated with slower deterioration of renal function in comparison to Vitamin K antagonists (VKAs). Hence, a NOAC should be used in preference to VKAs in all NOAC-eligible patients with AF and CKD. Regarding patients with end-stage renal dysfunction and those on dialysis or renal replacement therapy, the use of NOAC should be considered in line with locally relevant formal recommendations.

Exercise modulates sympathetic and vascular function in chronic kidney disease

BACKGROUNDChronic kidney disease (CKD) is characterized by chronic overactivation of the sympathetic nervous system (SNS), which increases the risk of cardiovascular (CV) disease and mortality. SNS overactivity increases CV risk by multiple mechanisms, including vascular stiffness. We tested the hypothesis that aerobic exercise training would reduce resting SNS activity and vascular stiffness in patients with CKD.METHODSIn this randomized controlled trial, sedentary older adults with CKD underwent 12 weeks of exercise (cycling, n = 32) or stretching (an active control group, n = 26). Exercise and stretching interventions were performed 20-45 minutes/session at 3 days/week and were matched for duration. Primary endpoints include resting muscle sympathetic nerve activity (MSNA) via microneurography, arterial stiffness by central pulse wave velocity (PWV), and aortic wave reflection by augmentation index (AIx).RESULTSThere was a significant group × time interaction in MSNA and AIx with no change in the exercise group but with an increase in the stretching group after 12 weeks. The magnitude of change in MSNA was inversely associated with baseline MSNA in the exercise group. There was no change in PWV in either group over the study period.CONCLUSIONOur data demonstrate that 12 weeks of cycling exercise has beneficial neurovascular effects in patients with CKD. Specifically, exercise training safely and effectively ameliorated the increase in MSNA and AIx observed over time in the control group. This sympathoinhibitory effect of exercise training showed greater magnitude in patients with CKD with higher resting MSNA.TRIAL REGISTRATIONClinicalTrials.gov, NCT02947750.FUNDINGNIH R01HL135183; NIH R61AT10457; NIH NCATS KL2TR002381; and NIH T32 DK00756; NIH F32HL147547; and VA Merit I01CX001065.

Chronic kidney disease progression in aged patients

PURPOSE

Chronic kidney disease (CKD) is a major morbidity, and its prevalence increases with age. However, there appears to be some confusion about the prognosis of CKD in aged patients, because, it has its own characteristics different from youngers. In this study, we investigated the progression of CKD and related factors in aged patients.

METHODS

This was a retrospective study including 334 patients over 80 years of age that were diagnosed with stage 3-4 CKD at our CKD clinic. CKD progression was assessed as an annual decline in the estimated glomerular filtration rate (eGFR). Comorbidities were globally categorized with the Charlson comorbidity index (CCI), but diabetes mellitus, hypertension, and cardiac morbidities were evaluated separately. Patients were grouped as either 'progression to end-stage renal disease (ESRD)' or 'others'.

RESULTS

During the follow-up period, 191 (57.2%) patients exhibited progression; the annual median eGFR declined by 0.8 ml/min/1.73 m². Only 27 (8.1%) of these patients progressed to ESRD. In univariant and multivariate models, respectively, progressing to ESRD was significantly associated with cardiac comorbidities (p < 0.001, p < 0.001), proteinuria (p < 0.001, p = 0.03), and the baseline eGFR value (p < 0.001, p < 0.001).

CONCLUSION

In aged patients, CKD progressed slowly, but particularly high initial creatinine levels and proteinuria could be indicator of progression. In addition, cardiac comorbidities may facilitate progression to ESRD.

Implications of Kidney Disease in the Cardiac Patient

Cardiovascular and renal diseases share common pathophysiological grounds, risk factors, and therapies. The 2 entities are closely interlinked and often coexist. The prevalence of kidney disease among cardiac patients is increasing. Patients have an atypical clinical presentation and variable disease manifestation versus the general population. Renal impairment limits therapeutic options and worsens prognosis. Meticulous treatment and close monitoring are required to ensure safety and avoid deterioration of kidney and heart functions. This review highlights recent advances in the diagnosis and treatment of cardiac pathologies, including coronary artery disease, arrhythmia, and heart failure, in patients with decreased renal function.

Atrial Fibrillation – An Orchestra of Classic and Modern Risk Factors

Over the past years, prevention and control of risk factors has begun to play an important role in the management of patients prone to develop atrial fibrillation (AF). A considerable number of risk factors that contribute to the creation of a predisposing substrate for AF has been identified over the years. Although certain AF risk factors such as age, gender, genetic predisposition, or race are unmodifiable, controlling modifiable risk factors may represent an invaluable tool in the management of AF patients. In the recent decades, numerous studies have evaluated the mechanisms linking different risk factors to AF, but the exact degree of atrial remodeling induced by each factor remains unknown. Elucidating these mechanisms is essential for initiating personalized therapies in patients prone to develop AF. The present review aims to provide an overview of the most relevant modifiable risk factors involved in AF occurrence, with a focus on the mechanisms by which these factors lead to AF initiation and perpetuation.

Vascular α1-adrenergic sensitivity is enhanced in chronic kidney disease

Chronic kidney disease (CKD) is often complicated by difficult-to-control hypertension, in part due to chronic overactivation of the sympathetic nervous system (SNS). CKD patients also exhibit a greater increase in arterial blood pressure for a given increase in sympathetic nerve activation, suggesting an augmented vasoconstrictive response to SNS activation (i.e., neurovascular transduction). One potential mechanism of increased sympathetic neurovascular transduction is heightened sensitivity of the vascular α₁-adrenergic receptors (α₁ARs), the major effectors of vasoconstriction in response to norepinephrine release at the sympathetic nerve terminals. Therefore, we hypothesized that patients with CKD have increased vascular α₁AR sensitivity. We studied 32 patients with CKD stages III and IV (age 59.9 ± 1.3 yr) and 19 age-matched controls (CON, age 63.2 ± 1.6 yr). Using a linear variable differential transformer (LVDT), we measured change in venoconstriction in response to exponentially increasing doses of the selective α₁AR agonist phenylephrine (PE) administered sequentially into a dorsal hand vein. Individual semilogarithmic PE dose-response curves were constructed for each participant to determine the PE dose at which 50% of maximum venoconstriction occurred (ED₅₀), reflecting α₁AR sensitivity. In support of our hypothesis, CKD patients had a lower PE ED₅₀ than CON (CKD = 2.23 ± 0.11 vs. CON = 2.63 ± 0.20, P = 0.023), demonstrating increased vascular α₁AR sensitivity. Additionally, CKD patients had a greater venoconstrictive capacity to PE than CON (P = 0.015). Augmented α₁AR sensitivity may contribute mechanistically to enhanced neurovascular transduction in CKD and may explain, in part, the greater blood pressure reactivity exhibited in these patients.

Association of B-Type Natriuretic Peptide Level With Residual Kidney Function in Incident Peritoneal Dialysis Patients

BACKGROUND

Residual kidney function (RKF) is an important factor influencing both technique and patient survival in peritoneal dialysis (PD) patients. B-type natriuretic peptide (BNP) is considered a marker of cardio-renal syndrome. The relationship between BNP and RKF in PD patients remains unclear.

METHODS

We conducted a prospective study of 89 patients who had started and continued PD for 6 months or more in Kyushu University Hospital between June 2006 and September 2015. Participants were divided into low BNP (≤ 102.1 ng/L) and high BNP (> 102.1 ng/L) groups according to median plasma BNP level at PD initiation. The primary outcome was RKF loss, defined as 24-hour urine volume less than 100 mL. We estimated the association between BNP and RKF loss using a Kaplan-Meier method and Cox proportional hazards model and compared the rate of RKF decline between the 2 groups. To evaluate the consistency of the association, we performed subgroup analysis stratified by baseline characteristics.

RESULTS

During the median follow-up of 30 months, 30 patients lost RKF. Participants in the high BNP group had a 5.87-fold increased risk for RKF loss compared with the low BNP group after adjustment for clinical and cardiac parameters. A high plasma BNP level was more clearly associated with RKF loss in younger participants compared with older participants in subgroup analysis.

CONCLUSIONS

B-type natriuretic peptide may be a useful risk marker for RKF loss in PD patients. The clinical importance of plasma BNP level as a marker of RKF loss might be affected by age.

Correlation of Blood Pressure in End-Stage Renal Disease with Platelet Cytosolic Free Calcium Concentration during Treatment of Renal Anemia with Recombinant Human Erythropoietin

The hemodynamic hallmark of hypertension complicating the treatment of renal anemia with recombinant human erythropoietin (rHu-EPO) is increased total peripheral vascular resistance, but the mechanisms underlying the arteriolar vasoconstriction are still an enigma. We studied body fluid volumes, plasma renin activity, plasma norepinephrine, and calcium metabolism in platelets in 40 previously normotensive hemodialysis patients before and after 12 weeks of rHu-EPO treatment. Partial correction of anemia caused a rise in arterial pressure (94 ± 6 mmHg vs 124 ± 7 mmHg, p < 0.05) and in platelet cytosolic calcium concentration (113 ± 5 nM vs 171 ± 18 nM, p < 0.05) in eight patients. Hypertensive patients had significantly higher plasma noradrenaline concentrations, but they did not differ significantly in body fluid volumes and plasma renin activities. There was a close correlation between free calcium concentration in platelets and mean arterial pressure in patients developing rHu-EPO-induced-hypertension (r = 0.95). Short-term antihypertensive treatment resulted in a reduction of free calcium concentrations in platelets and a concomitant fall in blood pressure. The main results of the present studies suggest that rHu-EPO-induced hypertension might be associated with altered cellular calcium homeostasis and hyperactivity of the sympathetic nervous system. If rHu-EPO therapy induces alterations of pressor factors or the hormone itself raises the cytosolic calcium not only in platelets but also in vascular smooth muscle cells, altered cellular calcium influx may contribute to the arteriolar vasoconstriction.

Abnormalities associated with progressive aortic vascular dysfunction in chronic kidney disease

Increased stiffness of large arteries in chronic kidney disease (CKD) has significant clinical implications. This study investigates the temporal development of thoracic aortic dysfunction in a rodent model of CKD, the Lewis polycystic kidney (LPK) rat. Animals aged 12 and 18 weeks were studied alongside age-matched Lewis controls (total n = 94). LPK rodents had elevated systolic blood pressure, left ventricular hypertrophy and progressively higher plasma creatinine and urea. Relative to Lewis controls, LPK exhibited reduced maximum aortic vasoconstriction (R_max) to noradrenaline at 12 and 18 weeks, and to K⁺ (12 weeks). Sensitivity to noradrenaline was greater in 18-week-old LPK vs. age matched Lewis (effective concentration 50%: 24 × 10⁻⁹ ± 78 × 10⁻¹⁰ vs. 19 × 10⁻⁸ ± 49 × 10⁻⁹, P < 0.05). Endothelium-dependent (acetylcholine) and -independent (sodium nitroprusside) relaxation was diminished in LPK, declining with age (12 vs. 18 weeks R_max: 80 ± 8% vs. 57 ± 9% and 92 ± 6% vs. 70 ± 9%, P < 0.05, respectively) in parallel with the decline in renal function. L-Arginine restored endothelial function in LPK, and L-NAME blunted acetylcholine relaxation in all groups. Impaired nitric oxide synthase (NOS) activity was recovered with L-Arginine plus L-NAME in 12, but not 18-week-old LPK. Aortic calcification was increased in LPK rats, as was collagen I/III, fibronectin and NADPH-oxidase subunit p47 (phox) mRNAs. Overall, our observations indicate that the vascular abnormalities associated with CKD are progressive in nature, being characterized by impaired vascular contraction and relaxation responses, concurrent with the development of endothelial dysfunction, which is likely driven by evolving deficits in NO signaling.

Chronic Kidney Disease and Atrial Fibrillation: A Contemporary Overview

Chronic kidney disease (CKD) is associated with substantial cardiovascular morbidity, including myocardial infarction, heart failure and stroke. Similar to CKD, atrial fibrillation (AF) is a prevalent arrhythmia that increases risk for both stroke and overall mortality. Recent studies demonstrate that both prevalence and incidence of AF is higher in patient with versus without renal impairment and risk for developing AF increases as renal function worsens. Potential mechanisms for the higher burden of AF in CKD patients include but are not limited to augmented sympathetic tone, activation of the renin-angiotensin-aldosterone system and myocardial remodeling. Similar to the general population, AF confers an increased risk for both stroke and overall mortality in the CKD population. The safety and efficacy of antithrombotic therapy across the spectrum of CKD remains unknown, however, as patients with advanced renal failure are frequently excluded from randomized trials. While treatment with vitamin K antagonists appears to reduce ischemic complications without significant bleeding harm in patients with mild to moderate CKD and AF, the risk benefit ratio of anticoagulation among thosewith advanced renal failure on dialysis requires further investigation. Prospective, randomized trials are war ranted to define the impact of antithrombotic therapy on reducing stroke risk in patients with both AF and CKD.

Effect of medial calcification on vascular function in uremia

The contribution of medial calcification to vascular dysfunction in renal failure is unknown. Vascular function was measured ex vivo in control, noncalcified uremic, and calcified uremic aortas from rats with adenine-induced renal failure. Plasma urea was 16 ± 4, 93 ± 14, and 110 ± 25 mg/dl, and aortic calcium content was 27 ± 4, 29 ± 2, and 4,946 ± 1,616 nmol/mg dry wt, respectively, in the three groups. Maximal contraction by phenylephrine (PE) or KCl was reduced 53 and 63% in uremic aortas, and sensitivity to KCl but not PE was increased. Maximal relaxation to acetylcholine was impaired in uremic aortas (30 vs. 65%), and sensitivity to nitroprusside was also reduced, indicating some impairment of endothelium-independent relaxation as well. None of these parameters differed between calcified and noncalcified uremic aortas. However, aortic compliance was reduced in calcified aortas, ranging from 17 to 61% depending on the severity of calcification. We conclude that uremic vascular calcification, even when not severe, significantly reduces arterial compliance. Vascular smooth muscle and endothelial function are altered in renal failure but are not affected by medial calcification, even when severe.

Hypertension Secondary to PHPT: Cause or Coincidence?

Primary hyperparathyroidism (PHPT) may be associated with arterial hypertension. The underlying mechanisms are not fully understood and reversibility by parathyroid surgery is controversial. This study aimed to characterize pressor hormones, vascular reactivity to norepinephrine, and cytosolic-free calcium in platelets in 15 hypertensive patients with hypercalcaemic PHPT before and after successful parathyroidectomy and to compare them with 5 pre-hypertensive patients with normocalcaemic PHPT, 8 normotensive patients with hypercalcaemic PHPT and 15 normal controls. Hypertensive patients with hypercalcaemic PHPT had slightly higher levels of pressor hormones (P < 0.05), enhanced cardiovascular reactivity to norepinephrine (P < 0.05) and increased cytosolic calcium in platelets (P < 0.05) than controls. Pre-hypertensive patients with normocalcaemic PHPT had intermediate values of increased cardiovascular reactivity and cytosolic calcium. Normotensive patients with hypercalcaemic PHPT and normotensive controls had comparable pressor hormone concentrations and intracellular calcium levels. Successful parathyroidectomy was associated with normal blood pressure values and normalisation of pressor hormone concentrations, cardiovascular pressor reactivity and cytosolic free calcium. Our results suggest that parathyroid hypertension is mediated/maintained, at least in part, by functional alterations of vascular smooth muscle cells and can be cured by parathyroidectomy in those patients who do not have primary hypertension.

Sympathetic activation in chronic renal failure

The potential involvement of sympathetic overactivity has been neglected in this population despite accumulating experimental and clinical evidence suggesting a crucial role of sympathetic activation for both progression of renal failure and the high rate of cardiovascular events in patients with chronic kidney disease. The contribution of sympathetic neural mechanisms to the occurrence of cardiac arrhythmias, the development of hypertension, and the progression of heart failure are well established; however, the exact mechanisms contributing to heightened sympathetic tone in patients with chronic kidney disease are unclear. This review analyses potential mechanisms underlying sympathetic activation in chronic kidney disease, the range of adverse consequences associated with this activation, and potential therapeutic implications resulting from this relationship.

Sympathetic hyperactivity in hypertensive chronic kidney disease patients is reduced during standard treatment

Standard treatment in chronic kidney disease (CKD) patients includes an angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker. CKD is often characterized by sympathetic hyperactivity. This study investigates the prevalence of sympathetic hyperactivity (quantified by assessment of muscle sympathetic nerve activity [MSNA]) in a sizable group of patients with CKD and assessed whether chronic angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker normalizes increased MSNA. In 74 CKD patients (creatinine clearance 54+/-31 mL/min), MSNA, blood pressure, and plasma renin activity were measured in the absence of antihypertensive drugs except for diuretics. In a subgroup of 31 patients, another set of measurements was obtained after > or =6 weeks of enalapril (10 mg PO), losartan (100 mg PO), or eprosartan (600 mg PO). Patients as compared with control subjects (n=82) had higher mean arterial pressure (113+/-13 versus 89+/-7 mm Hg), MSNA (31+/-13 versus 19+/-7 bursts per minute), and log plasma renin activity (2.67+/-036 versus 2.40+/-0.32 fmol/L per second; all P<0.001). During angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker therapy (n=31), mean arterial pressure (115+/-11 to 100+/-9 mm Hg) and MSNA (33+/-11 to 25+/-9 bursts per minute) decreased (both P<0.01) but were still higher than in control subjects (both P<0.01). Multiple regression analysis identified age and plasma renin activity as predictive for MSNA. In conclusion, sympathetic hyperactivity occurs in a substantial proportion of hypertensive CKD patients. Angiotensin-converting enzyme inhibitor or angiotensin II receptor blocker treatment reduces but does not normalize MSNA.

Risk-benefit ratio of angiotensin antagonists versus ACE inhibitors in end-stage renal disease

The effective treatment of hypertension is an extremely important consideration in patients with end-stage renal disease (ESRD). Virtually any drug class--with the possible exception of diuretics--can be used to treat hypertension in the patient with ESRD. Despite there being such a wide range of treatment options, drugs which interrupt the renin-angiotensin axis are generally suggested as agents of choice in this population, even though the evidence in support of their preferential use is quite scanty. ACE inhibitors, and more recently angiotensin antagonists, are the 2 drug classes most commonly employed to alter renin-angiotensin axis activity and therefore produce blood pressure control. ACE inhibitor use in patients with ESRD can sometimes prove an exacting proposition. ACE inhibitors are variably dialysed, with compounds such as catopril, enalapril, lisinopril and perindopril undergoing substantial cross-dialyser clearance during a standard dialysis session. This phenomenon makes the selection of a dose and the timing of administration for an ACE inhibitor a complex issue in patients with ESRD. Furthermore, ACE inhibitors are recognised as having a range of nonpressor effects that are pertinent to patients with ESRD. Such effects include their ability to decrease thirst drive and to decrease erythropoiesis. In addition, ACE inhibitors have a unique adverse effect profile. As is the case with their use in patients without renal failure, use of ACE inhibitors in patients with ESRD can be accompanied by cough and less frequently by angioneurotic oedema. In the ESRD population, ACE inhibitor use is also accompanied by so-called anaphylactoid dialyser reactions. Angiotensin antagonists are similar to ACE inhibitors in their mechanism of blood pressure lowering. Angiotensin antagonists are not dialysable and therefore can be distinguished from a number of the ACE inhibitors. In addition, the adverse effect profile for angiotensin antagonists is remarkably bland, with cough and angioneurotic oedema rarely, if ever, occurring. In patients with ESRD, angiotensin antagonists are also not associated with the anaphylactoid dialyser reactions which occur with ACE inhibitors. The nonpressor effects of angiotensin antagonists--such as an influence on thirst drive and erythropoiesis--have not been explored in nearly the depth, as they have been with ACE inhibitors. Although ACE inhibitors have not been compared directly to angiotensin antagonists in patients with ESRD, angiotensin antagonists possess a number of pharmacokinetic and adverse effect characteristics, which would favour their use in this population.

Hypertension in end-stage renal disease

Patients with moderate to severe renal disease have a very high incidence of hypertension. In end-stage renal disease (ESRD) this is true regardless of the nature of the underlying renal disease. Nevertheless, patients with glomerular diseases and autosomal dominant polycystic kidney disease are particularly vulnerable. Evidence is presented that ESRD hypertension is the result of extracellular volume expansion, increased or inappropriate response of the renin-angiotensin system and overactivity of the sympathetic system. In addition, the role of endothelin-1, nitric oxide and other vasodilators, and abnormal ion channels in generating high blood pressure, is considered.

Hypertension secondary to early-stage kidney disease: the pathogenetic role of altered cytosolic calcium (Ca2+) homeostasis of vascular smooth muscle cells

We have examined cardiovascular pressor responsiveness to infused norepinephrine (NE) as related to endogenous plasma NE and plasma renin and to platelet free cytosolic (Ca2+) in 36 patients with early-stage kidney disease and 27 matched normal subjects. The 27 hypertensive patients and the normal subjects did not differ in blood volume, plasma renin, and NE; however, the hypertensive patients had a higher exchangeable body sodium content. Basal plasma NE levels, the relationship between plasma NE measured during NE infusion and the corresponding NE infusion rate, as well as the total plasma clearance for NE did also not differ significantly between the two study groups. In contrast, the threshold or pressor doses of infused NE significantly decreased in the patients with kidney disease. Antihypertensive pharmacotherapy with (Ca2+) channel blockers and/or loop diuretics normalized blood pressure and cardiovascular NE hyperresponsiveness and reduced blood volume, exchangeable body sodium, and platelet free cytosolic (Ca2+). In contrast, experimental digitalisation as a model for in vivo sodium/potassium adenosine triphosphatase inhibition augmented NE responsiveness and raised platelet free cytosolic (Ca2+). Incubation of platelets from normal subjects with plasma ultrafiltrate from hypertensive patients gave evidence for an endogenous factor capable to raise free cytosolic (Ca2+) and to act synergistically with digoxin. Hypertension secondary to early-stage kidney disease is related to an impairment of sodium excretion leading to an expansion of blood volume and exchangeable body sodium. This may result in increased secretion of endogenous factors, leading to alterations of cytosolic (Ca2+) homeostasis of vascular smooth muscle cells followed by elevated peripheral resistance and thus blood pressure.

Atrial natriuretic peptide and parathyroid hormone (1-84) in relation to noradrenaline induced changes in blood pressure in uraemic and healthy subjects

In order to evaluate the hormonal regulation of blood pressure (BP) in uraemia 12 patients on chronic maintenance dialysis and 14 healthy controls were studied. BP and plasma concentrations of atrial natriuretic peptide (ANP), cyclic 3',5'-guanosine monophosphate (cGMP), and intact parathyroid hormone (PTH(1-84)) were determined before, during, and after a 60 min noradrenaline infusion 0.1 micrograms kg-1 body wt. min-1. Mean BP increased to the same extent in the uraemic patients (median 15 mmHg, range 6-25 mmHg) as in the controls (12 mmHg, 5-25 mmHg). ANP increased during noradrenaline infusion both in patients (7.2 to 8.3 pmol/l, medians, p < 0.01) and in controls (4.4 to 6.0 pmol/l, p < 0.01), and so did cGMP (patients: 31.6 to 35.9 nmol/l, p < 0.05; controls: 6.6 to 8.7 nmol/l, p < 0.01). PTH(1-84) was higher in the uraemic patients than in the controls, but was unchanged during noradrenaline infusion in both groups. Correlation analyses gave no evidence of a direct relation between BP and ANP, but basal PTH(1-84) was negatively correlated to basal mean BP in the patients (rho = -0.615, p < 0.05), but not in the controls. In conclusion, noradrenaline induced similar elevations of BP in dialysis patients as in healthy controls despite elevated ANP and PTH(1-84) in the patients, and ANP release was stimulated in both groups. PTH(1-84) may participate in blood pressure regulation in uraemic patients.

Modulation of platelet Ca2+ homeostasis by hypertensive plasma factor(s) derived from patients with early-stage renal disease

To determine whether blood-borne factors in hypertension accompanying early-stage kidney disease might be responsible for altered cellular calcium homeostasis, we measured changes in cytosolic calcium before and after incubating platelets in plasma ultrafiltrates from normotensive and hypertensive renal patients. With the use of the chelating agent quin 2, we found the free-calcium concentrations in platelets to be higher in the hypertensive than in the normotensive group. When both groups of participants were combined, a direct correlation was found between arterial pressure and cytosolic calcium. The cytosolic calcium concentration in platelets of normotensive renal patients increased after incubation with plasma from patients with untreated renal hypertension, but it was unchanged after incubation with plasma from normotensive subjects. These data indicate that the total cell burden of calcium is increased in platelets of hypertensive patients with early-stage renal disease, and that plasma from these patients contains a substance that is capable of increasing the cytosolic calcium concentration in platelets. If the plasma factor (or factors) acts not only on platelets, but also on vascular smooth muscle cells, it may contribute to the increased peripheral vascular resistance associated with hypertension of renal origin.

Effect of circulating factors on vascular smooth muscle contraction and its calcium uptake in uremia

Uremia is often associated with alterations in calcium metabolism and vascular smooth muscle function in hypertension and atherosclerosis. The ways in which these conditions inter-relate are not clearly understood. In order to study the possibility that circulating factors might influence smooth muscle function, experiments were performed on rat aortic strips. The serum from both uremic patients and rats enhanced the norepinephrine-induced contraction (NEIC) and net 45-calcium uptake in rat aortic strips. In a similar manner, the serum of parathyroidectomized uremic rats also increased the NEIC, whereas verapamil reduced the aortic response to levels below those of the control, in the presence of uremic serum. These findings suggest that in both chronic (patients) and early (rats) stages of uremia, there is a circulating factor, different from parathyroid hormone, that affects calcium uptake and vascular smooth muscle contraction.

Platelet cytosolic free calcium concentration in hypertension associated with early stage kidney disease

Chronic hypertension accompanying early stage kidney disease is characterized by increased vascular resistance, but the underlying processes responsible for the enhanced vascular tone are unclear. We studied free calcium levels in blood platelets with the fluorescent dye quin-2. Platelets have many features in common with vascular smooth muscle cells. The cytosolic calcium concentration in platelets was elevated in 27 renal hypertensive patients, who were compared with 12 normotensive subjects (P less than 0.001). There was a close correlation between the free calcium level and mean blood pressure (r = 0.88, P less than 0.001). Short-term antihypertensive treatment with a calcium entry blocker or a diuretic resulted in a significant reduction in cytosolic calcium (P less than 0.05), and this correlated with the fall in blood pressure (r = 0.95, P less than 0.001). These data suggest an integrative contributory role of calcium in the pathophysiology of hypertension accompanying early stage kidney disease.

Arterial hypotension in chronic hemodialyzed patients

We studied in 32 patients on maintenance hemodialysis (duration of treatment 6 to 133 months) whether duration of dialysis treatment affects blood pressure, plasma noradrenaline levels and alpha 2-adrenoceptor density (assessed in platelet membranes by 3H-yohimbine binding). Plasma noradrenaline levels were a significant inverse correlation to platelet alpha 2-adrenoceptor density. In addition, mean arterial blood-pressure, plasma noradrenaline levels and platelet alpha 2-adrenoceptor density were significantly related to the duration of treatment: with increasing duration of treatment plasma noradrenaline levels increased, whereas mean arterial blood-pressure and platelet alpha 2-adrenoceptor density decreased. Furthermore, changes in mean arterial blood-pressure were inversely related to plasma noradrenaline levels and positively to platelet alpha 2-adrenoceptor density. Platelet alpha 2-adrenoceptor changes were accompanied by similar alterations in (vascular) alpha 1-adrenoceptor responsiveness (assessed by blood pressure responses to i.v. injections of phenylephrine); in hypotensive hemodialysis patients, who had high, plasma noradrenaline levels and low, platelet alpha 2-adrenoceptor density, the dose of phenylephrine necessary to increase systolic blood pressure by 20 mm Hg was nearly twice as high as in normotensive dialysis patients and healthy controls. In autonomic tests, Valsalva-ratio was lower in hypotensive than in normotensive dialysis patients and healthy controls, whereas no differences were found in blood pressure and heart rate responses during sustained hand-grip exercise as well as in beat-to-beat variation during deep breathing.(ABSTRACT TRUNCATED AT 250 WORDS)

Cardiovascular responses in rats with chronic renal failure

Cardiovascular responses were determined in rats with chronic renal failure (CRF) produced by five sixths nephrectomy and in sham-operated rats. The conscious systolic blood pressure of rats with CRF was significantly higher than the pressure in controls although, after anaesthesia, there were no significant differences in the mean arterial pressure between the two groups of rats. The pressor responses to noradrenaline in rats with CRF were not significantly different from those recorded in sham-operated controls. The bradycardia elicited by electrical stimulation of the vagus nerve was significantly diminished in rats with CRF. However, indomethacin treatment (1 mg kg-1 s.c. twice daily for 2 days) abolished the differences in response to vagal stimulation. Changes in heart rate in response to electrical stimulation of the cervical sympathetic nerve and to bolus i.v. injections of isoprenaline and carbachol were similar in rats with CRF and controls. The most notable disturbance of cardiovascular function in rats with CRF is the diminished cardiac chronotropic response to vagal stimulation which appears to be mediated by a presynaptic action of prostaglandins.

Plasma and urinary catecholamines as related to renal function in man

To assess the relationship between renal plasma flow (ERPF) or glomerular filtration rate (GFR) and the levels of norepinephrine (NE) or epinephrine (E) in plasma or urine in the presence of progressive degrees of non-oliguric renal functional impairment, these variables were assessed simultaneously in 18 normal subjects, 72 with parenchymal kidney disease and 14 with essential hypertension. ERPF and GFR were lower (P less than 0.01 to 0.001) in the groups with renal disease (mean +/- SD, 340 +/- 230 and 68 +/- 43 ml/min/1.73 m2, respectively) or essential hypertension (434 +/- 101 and 97 +/- 25 ml/min/1.73 m2) than normal subjects (597 +/- 133 and 118 +/- 14 ml/min/1.73 m2). Plasma and urinary NE and E did not differ significantly among groups and were unrelated with ERPF or GFR (range 4 to 160 ml/min/1.73 m2), except for reduced (P less than 0.001) urinary NE and E excretion in the presence of a GFR less than 20 ml/min. Subgroups with renal disease and a normal (N = 39) or high blood pressure (N = 33) also were comparable in their plasma and urinary NE and E, while ERPF and GFR tended to be lower in hypertensive patients. It is concluded that a chronic reduction in excretory kidney function may have no relevant impact on circulating levels of NE and E per se, although their urinary excretion falls distinctly at the stage of advanced renal failure. These aspects deserve consideration when pathogenetic or diagnostic studies of catecholamines are performed in normotensive or hypertensive patients with impaired kidney function.

Relationship of angiotensin II, aldosterone, arginine vasopressin, adrenaline and noradrenaline in plasma, blood and extracellular volumes to blood pressure in chronic glomerulonephritis

Blood volume, extracellular volume, blood pressure and the plasma levels of angiotensin II, aldosterone, adrenaline, noradrenaline and arginine vasopressin were determined in sixteen normotensive (group 1) and thirteen hypertensive patients (group 2) with chronic glomerulonephritis and in eleven normotensive control subjects (group 3). Blood volume and extracellular volume did not differ between the groups and no significant differences were found in any of the hormones measured when comparing group 1 or group 2 with group 3. In the hypertensives but not in the normotensives or control subjects, a highly significant positive correlation was found between diastolic blood pressure and blood volume (rho = 0.75, P less than 0.01) and between diastolic blood pressure and extracellular volume (rho = 0.74, P less than 0.01). Blood volume and extracellular volume correlated (P less than 0.05) in each of the groups. In conclusion, although no expansion of either blood or extracellular volume was found in chronic glomerulonephritis, a positive volume-pressure relationship could be demonstrated in hypertensive patients suggesting a role of volume factors in the pathogenesis in early stage chronic glomerulonephritis. The study does not give support to a major role of either angiotensin II, arginine vasopressin or catecholamines in the maintenance of nonmalignant hypertension in early stage chronic glomerulonephritis.

[Sympathetic activity in terminal renal failure and kidney transplants]

Blood pressure as well as noradrenaline, creatinine and electrolytes in blood and urine were compared in normal controls (n = 25), patients with chronic renal failure (n = 39), patients with continuous ambulatory peritoneal dialysis (CAPD) (n = 28) and haemodialysis patients before and after renal transplantation (n = 63). The average blood pressures of the control group and the CAPD patients were lower than those of the renal failure patients without and with haemodialysis. After renal transplantation elevated blood pressure normalised in 18% within the following 6 months. In all groups of patients with renal failure the mean noradrenaline plasma concentration was increased more than three-fold of normal values: 1,470 pg/ml in patients with chronic renal failure, 1,366 pg/ml in CAPD patients and 1,284 pg/ml in patients with haemodialysis. No correlation was found between these elevated noradrenaline plasma levels and blood pressure. However, there was a significant correlation between noradrenaline excretion and sodium excretion. Compared to the controls, the urine excretion of noradrenaline was significantly lower in patients with chronic renal failure and almost zero in patients with dialysis treatment. Two days after renal transplantation the mean noradrenaline urine excretion increased to 15.7 +/- 1.8 micrograms/day and 4 days after transplantation the noradrenaline plasma concentration decreased to 592 +/- 155 pg/ml. Nine months after renal transplantation the creatinine clearance was 76 ml/min and the mean noradrenaline plasma concentration 438 +/- 153 pg/ml. It is concluded that in chronic renal failure the level of noradrenaline plasma concentration is dependent on renal function.

Adrenergic activity and peripheral hemodynamics in relation to sodium sensitivity in patients with essential hypertension

In 25 outpatients with essential hypertension, sodium sensitivity, defined as the difference in mean arterial pressure (delta MAP) between 2 weeks of high-sodium (300 mmol per day) and 2 weeks of low-sodium (LS) intake (50-100 mmol per day), was studied in relation to the plasma norepinephrine (NE) level, NE release, and pressor response to intravenous NE. In addition, forearm blood flow (FBF) was measured by plethysmography. There were two control periods of regular sodium intake, one of 4 weeks' duration at the beginning of the study and one of 2 weeks' duration at the end. The delta MAP ranged from +18 to -8 mm Hg. The eight patients in whom delta MAP was greater than 10 mm Hg were regarded as salt-sensitive. When compared with salt-insensitive subjects, salt-sensitive patients had higher plasma NE levels in the control period (p less than 0.05) and after 2 weeks of HS intake (p less than 0.01). Sodium sensitivity was directly related to the change in plasma NE between the HS and LS periods (p less than 0.001). The NE release decreased in salt-insensitive subjects whereas it increased in salt-sensitive patients between the LS and HS periods. Changes in NE release were directly related to sodium sensitivity (p less than 0.05). The pressor response to NE was not significantly influenced by changes in sodium intake. The FBF fell in salt-sensitive patients and increased in salt-insensitive subjects between the LS and HS periods. Sodium sensitivity was directly related to the change in forearm vascular resistance (p less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Antihypertensive mechanism of the diuretic muzolimine in mild renal failure. Roles of sodium and cardiovascular norepinephrine responsiveness

Eighteen patients with mild impairment of renal function (glomerular filtration rate 65 +/- 5 ml/min:m +/- SEM) and hypertension (168/105 +/- 6/3 mmHg) were shown on average to have abnormally increased cardiovascular pressor responsiveness to infused norepinephrine (NE; p less than 0.05), whereas plasma and urinary NE, exchangeable body sodium and blood-volume did not differ significantly from normal. A slightly increased pressor responsiveness to angiotensin II was associated with a tendency to low plasma renin activity (PRA). Compared to placebo conditions, treatment with the loop-diuretic muzolimine in a mean dose of 35 +/- 2 mg/day for six weeks decreased blood-pressure and exchangeable sodium (p less than 0.05), and NE pressor responsiveness was restored to normal values, whilst plasma and urinary NE were not significantly changed. This was consistent with improvement of the initially abnormal relationship between NE levels and NE responsiveness factors. In contrast, the pressor dose of angiotensin II and PRA were increased to an approximatively similar extent during muzolimine treatment. These observations suggest that removal of body sodium and a decrease in NE reactivity without an equivalent increase in sympathetic nervous activity may be important complementary factors in the antihypertensive mechanisms of diuretic treatment in patients with mild renal functional impairment.