Anthony E.G. Raine

Adverse effect of chronic alcohol ingestion on cardiac performance in spontaneously hypertensive rats

We have compared the cardiac performance of four groups of rats: normotensive control rats (NCR) and spontaneously hypertensive rats (SHR) not drinking alcohol, and NCR and SHR drinking 20% alcohol (NCR-A and SHR-A, respectively), over a period of 6-9 months.

Acute reversal of cyclosporine nephrotoxicity by neutral endopeptidase inhibition in stable renal transplant recipients.

BACKGROUND Atrial natriuretic peptide and cyclosporine have opposing effects on renal hemodynamics and excretory function. METHODS Twelve male stable cyclosporine-treated renal transplant recipients received a single 100-mg i.v. dose of the neutral endopeptidase EC 24.11 inhibitor candoxatrilat in a double-blind, placebo-controlled cross-over study. Each study day consisted of 2 hr of baseline and 7 hr of postdose evaluation. RESULTS After administration of candoxatrilat, plasma atrial natriuretic factor rose from 12.8+/-1.6 (mean +/- SEM) to 44.1+/-6.8 pmol/L (P<0.001) in association with a threefold increase in urine cGMP excretion (573+/-195 pmol/min baseline to 1823+/-545 pmol/ min; P<0.001), marked natriuresis (207+/-34 micromol/min baseline to 416+/-62 micromol/min; P<0.001), fractional sodium excretion (3.3+/-0.5% baseline to 5.6+/-0.7%; P<0.01), and diuresis (3.4+/-0.5 ml/min baseline to 7.4+/-1 ml/min; P<0.001). All parameters remained elevated above baseline for the remaining 7-hr study period. In response to candoxatrilat, the glomerular filtration rate rose by 19% (P=0.01), renal plasma flow by 7% (P=0.04), renal blood flow by 13% (P=0.03) in association with an increase in filtration fraction from 24+/-2% to 28+/-2% (P=0.002) and small fall in renal vascular resistance from 0.38+/-0.04 to 0.30+/-0.04 mmHg x min x 1.73 m2 x ml(-1) (P=0.02). There was a fall in plasma angiotensin II without a change in plasma renin concentration or plasma aldosterone. Median urinary albumin excretion increased after candoxatrilat administration from 48 (3-131) to 114 (32-641) microg/min (P<0.01). CONCLUSIONS Acute neutral endopeptidase inhibition with candoxatrilat appears to reverse the adverse renal hemodynamic and renal excretory effects of cyclosporine in stable renal transplant recipients.

Recombinant Erythropoietin Increases Blood Pressure in Experimental Hypertension and Uraemia without Change in Vascular Cytosolic Calcium

The mechanism of erythropoietin-induced hypertension in dialysis patients is unclear. Intracellular calcium ([Ca2+]i) may be altered in both hypertension and uraemia, and the effects of both uraemia and r-HuEPO on vascular smooth muscle [Ca2+]i and blood pressure (BP) in Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) were therefore studied. Male WKY and SHR underwent partial nephrectomy or sham operation. Three weeks later a 28-day period of treatment with either r-HuEPO 100 U/kg, s.c., 3 times/week or buffer was commenced (n = 10-12 for each subgroup). BP was measured weekly, by noninvasive Doppler tail-cuff assessment. [Ca2+]i was measured following loading with fura-2 in pooled, primary aortic vascular smooth muscle cells (VSMC). Serum urea and creatinine rose 3- to 4-fold after partial nephrectomy. Treatment with r-HuEPO did not change renal function further in either uraemic or control WKY or SHR. Haemoglobin increased in both non-uraemic WKY (16.2-20.3 g/dl) and SHR (16.4-20.5 g/dl) and uraemic animals (WKY 13.9-20.9; SHR 13.8-18.8 g/dl; p < 0.01 for all changes) following 4 weeks of r-HuEPO treatment. BP was unaffected by r-HuEPO in WKY but increased in nonuraemic SHR (210-250; p < 0.01) and in uraemic SHR (224-251 mm Hg; p < 0.001) at 4 weeks. VSMC [Ca2+]i was higher in SHR than WKY (121 vs. 83 nmol/l; MANOVA p < 0.05) but no effect of uraemia or r-HuEPO on [Ca2+]i was detected. In conclusion, the hypertensive effects of r-HuEPO are augmented both in a genetic model of hypertension and in uraemia. Although VSMC [Ca2+]i was elevated in SHR, the further increase in BP induced by r-HuEPO was not associated with alterations in VSMC cytosolic calcium.

Comparison of Haemostatic Activity in Haemodialysis and Peritoneal Dialysis Patients with a Novel Technique, Haemostatometry

Bleeding due to impaired primary haemostasis is common in uraemia. However, thrombo-embolic episodes are also a clinical problem in dialysis patients. Platelet reactivity to shear stress (haemostasis, H1 and H2), exposure to collagen fibre (thrombus growth) and coagulation of flowing blood (clotting time, CT1 and CT2) were measured in non-anticoagulated blood samples taken immediately before and 18-24 h after haemodialysis (n = 26) and from patients maintained on continuous ambulatory peritoneal dialysis (CAPD, n = 30). H1 (p < 0.001), H2 (p < 0.01), percent thrombus growth rate (p < 0.03), CT1 (p < 0.01 and CT2 (p < 0.05) were restored towards normal after haemodialysis. Results obtained in the CAPD patients demonstrated that the mean values for formation of the haemostatic plug lay between the pre- and posthaemodialysis values; however, CT1 (p < 0.01) and CT2 (p < 0.05) were prolonged in CAPD compared with values after haemodialysis. These data, which indicate platelet function from non-anticoagulated blood and coagulation under flow conditions, (1) confirm that there is impaired haemostasis in uraemia; (2) demonstrate an improvement in haemostasis after haemodialysis; (3) show that peritoneal dialysis results in a haemostatic profile which falls between the pre- and posthaemodialysis pattern, and (4) show that neither dialysis modality returns haemostasis to normal.

Effects of Parathyroid Hormone and 1,25(OH2)D3 on Protein Glycation in Moderate Uraemia

Glucose intolerance in uraemia may be a consequence of secondary hyperparathyroidism. In this study fructosamine and glycated albumin have been used as markers of long-term glycaemic control in a group of pre-end-stage, non-diabetic uraemic patients with secondary hyperparathyroidism. The serum fructosamine level (mumol/100 g total protein) was significantly higher (p = 0.005) in uraemic patients (364 +/- 42) than in a group of 25 non-uraemic controls (332 +/- 27), but the content of glycated albumin did not differ (p > 0.05; 1.6 +/- 0.5 vs. 1.5 +/- 0.3%). In the uraemic patients, there was a significant relationship between serum 1,25-dihydroxycholecalciferol [1,25(OH2)D] (median 4.2, range 1.0-38 ng/l) and fructosamine (r = -0.66, p < 0.01; fructosamine = -2.76 1,25(OH2)D + 389), but not glycated albumin (r = -0.22, p > 0.1). No relationship existed between serum parathyroid hormone (median 15.4, range 7.0-55 pmol/l) and either glycated albumin or fructosamine (p > 0.1). In patients treated with oral calcitriol (0.25 microgram/day), significant reductions in serum parathyroid hormone after both 4 (p = 0.03) and 8 weeks (p = 0.02) and concomitant increases in serum 1,25(OH2)D (p < 0.02) after 8 weeks of treatment were not accompanied by any change in fructosamine, glycated albumin, total calcium, or ionized calcium (p > 0.05). Elevation of serum fructosamine in these patients is consistent with the impaired glucose tolerance of uraemia. The evidence presented supports a relationship between long-term glycaemic control and 1,25(OH2)D3, but not parathyroid hormone, in moderately uraemic patients with secondary hyperparathyroidism; however, serum fructosamine was not altered by treatment with calcitriol over an 8-week period.

PROLONGED ELEVATION OF PLASMA ATRIAL NATRIURETIC FACTOR DOES NOT INCREASE ERYTHROPOIETIN LEVELS IN PATIENTS WITH CHRONIC RENAL FAILURE

Prof. A.E.G. Raine, Department of Nephrology, St. Bartholomew’s Hospital, West Smithfield, London EC1A 7BE (UK) Dear Sir, Ervthropoietin (EPO) is produced by peritubular cells of the kidney in response to renal hypoxia [1]. In vitro, EPO production may be increased in a dose-dependent manner by atrial natriuretic factor (ANF), an effect mediated by increased cyclic guanosine monophosphate (GMP), the intracellular second messenger of ANF [2]. Inappropriately low EPO production is the major cause of renal anaemia in patients with chronic renal failure (CRF) and therefore agents which increase endogenous EPO production may be of clinical interest. Inhibitors of ANF metabolism by the enzyme neutral endopeptidase (EC.24.11) have recently become available [3]. We have previously shown that when administered acutely to patients with CRF, these agents produce a prolonged rise in plasma ANF concentration associated with a natriuresis greater than that seen in normal subjects [4] which suggests they may have a potential therapeutic role. We therefore examined the effect of prolonged plasma ANF elevation through acute neutral endopeptidase inhibition on serum EPO levels in patients with normal glomeru-lar filtration rate, or with moderate or severe CRF. Three groups, each consisting of 8 male patients, were studied: group 1 (normals), GFR106 ± 8 ml/min/1.73 m2 (mean ± SEM); group 2 (moderate CRF), GFR 64 ± 6 ml/ min/1.73 m2; group 3 (severe CRF), GFR 16 ± 3 ml/min/1.73 m2. Each patient received either the neutral endopeptidase inhibitor, candoxatrilat (Pfizer UK Ltd.) 100 mg intravenously or vehicle (saline) in a double-blind, randomised, crossover study. Plasma ANF (IRMA), urinary cyclic GMP excretion (RIA) and serum EPO (RIA) were measured at baseline, 3 h (peak ANF) and 7 h after administration. The results for the three groups are shown in table 1. ‘Peak’and 7hour post-dose results were compared with baseline using paired t tests if prior two-way analysis of variance achieved significance. Plasma ANF and urinary cyclic GMP excretion rose 2 to 3-fold from baseline in all three groups and remained elevated for at least 7 h in patients with CRF. Despite this, no significant change occurred in serum EPO concentration. No change occurred in any variable in response to vehicle administration. A rise in serum EPO concentration is usually seen within 1-2 h after the onset of stimuli which increase EPO production by the kidney [1].