David Geadah

Temporal effects of left versus right middle cerebral artery occlusion on spleen lymphocyte subsets and mitogenic response in Wistar rats.

The left and right neocortex of the brain has been shown to exert asymmetrical effects on the immune system. In the present study, we used a middle cerebral artery (MCA) occlusion model in Wistar rats to analyze the influence of unilateral CNS ischemia on spleen cell number and function. The occlusion time was 1 h, followed by reperfusion with survival for 0, 2, 7, 14, and 28 days. Changes in plasma norepinephrine levels were used as an index of peripheral sympathetic activity. Results showed that the total number of spleen cells significantly decreased after 2-28 days of survival in animals with cerebral ischemia compared to sham-operated controls. There was no change in the percentage of CD5(+)-CD4(+) T cells, MHC class II(+) cells, or ED1(+) macrophages. However, the percentage of CD5(+)-CD8(+) T cells decreased at 2 days, resulting in an increased CD4/CD8 ratio, and both parameters returned to control levels after 7 days. Mitogen-induced T and B lymphocyte proliferation increased after 0-28 days post-ischemia independently of the mitogen used. There was no difference in immune response or norepinephrine levels between left and right MCA occlusions. These results are consistent with the notion that cerebral ischemia induces mobilization of certain immune cells from the periphery to the brain, where they may contribute to the local inflammatory response. Additionally, the data indicate that cerebral ischemia is followed by a systemic activation of T and B lymphocytes. Absence of asymmetric effects of left versus right stroke, and failure to demonstrate any suppressive effects of left-sided lesions on lymphocyte proliferation, probably reflects the fact that these large cerebral ischemic lesions affect both cortical and subcortical areas.

Myoglobin clearance and removal during continuous venovenous hemofiltration.

Abstract Myoglobin has a relatively high molecular weight of 17,000 Da and is poorly cleared by dialysis (diffusion). However, elimination of myoglobin might be enhanced by an epuration modality based on convection for solute clearances. We present a single case of myoglobin-induced renal failure (peak creatine kinase level: 313,500 IU/l) treated by continuous venovenous hemofiltration (CVVH). Our purpose was to evaluate the efficiency of such a modality using an ultrafiltration rate of 2 to 3 l/h for myoglobin removal and clearance. The hemofilter was a 0.9 m2 polyacrylonitrile (AN69) membrane Multiflow-100 (Hospal-Gambro, St-Leonard, Canada) and the blood flow rate was maintained at 150 ml/min by an AK-10 pump (Hospal-Gambro, St-Leonard, Canada). The ultrafiltration bag was placed 60 cm below the hemofilter and was free of pump control or suction device. Serum myoglobin concentration was 92,000 μg/l at CVVH initiation and dropped to 28,600 μg/l after 18 h of the continuous modality. The mean sieving coefficient for myoglobin was 0.6 during the first 9 h of therapy and this decreased to 0.4 during the following 7 h. Mean clearance of myoglobin was 22 ml/min, decreasing to 14 ml/min during corresponding periods, while the mean ultrafiltration rates were relatively stable at 2,153 ± 148 ml/h and 2,074 ± 85 ml/h, respectively. In contrast to myoglobin, the sieving coefficeint for urea, creatinine, and phosphorus remained stable at 1.0 during the first 16 h of CVVH. More than 700 mg of myoglobin were removed by CVVH during the entire treatment.¶In conclusion, considerable amounts of myoglobin can be removed by an extracorporeal modality allowing important convective fluxes and middle molecule clearances, such as CVVH at a rate of 2 to 3 l/h using an AN69 hemofilter. If myoglobin clearance had been maintained at 22 ml/min, 32 l of serum would have been cleared per day. However, the sieving coefficient of myoglobin decreased over time, probably as a consequence of protein coating and/or blood clotting of the hemofilter. Whereas myoglobin can be removed by CVVH, it remains unknown at this point if such a modality, applied early, can alter or shorten the course of myoglobinuric acute renal failure.

Serum concentrations and clearances of folic acid and pyridoxal-5-phosphate during venovenous continuous renal replacement therapy.

Objective: To determine to what extent hydrosoluble vitamins are removed by continuous renal replacement therapy (CRRT); to evaluate clearances, removal rates, and evolution of serum concentrations of folic acid and pyridoxal-5′-phosphate (P-5′-P), the active moiety of vitamin B6 during CRRT. Design: A prospective, non-interventional, descriptive study on vitamin losses induced by CRRT. Setting: Medical and surgical intensive care units in a tertiary university-affiliated hospital. Patients: A total of ten critically ill patients in oligoanuric acute renal failure (five treated by continuous venovenous hemofiltration and five by continuous venovenous hemodiafiltration) with a mean effluent rate of 1801 ± 468 ml/h. Nutritional support was not modified and additional vitamin supplements were not provided during study periods. Measurements and results: Concentrations of folic acid and P-5′-P were determined daily during CRRT. Samples for folic acid, P-5′-P, urea, and creatinine were taken simultaneously from the blood at the dialyzer inlet and from the effluent, at CRRT initiation, and daily thereafter over an average of 3.4 ± 1.2 days. Samples were processed by immunochemiluminescence for folic acid and by radioenzymatic assay for P-5′-P determinations with normal ranges above 6.8 nmol/l and from 11.5 to 179.3 nmol/l, respectively. Marked decreases in serum folic acid and P-5′-P concentrations were noticed over time with mean daily reductions of 12.6 and 13.7 %. Serum folic acid concentrations decreased from 42.7 to 16.0 nmol/l and serum P-5′-P decreased from 14.4 to 5.0 nmol/l in the blood coming in to the dialyzer over the study period. Clearances and removal rates were determined from the effluent side. During CRRT, mean (± SEM) folic acid and P-5′-P clearances were 20.5 ± 6.3 ml/min (n = 34) and 13.2 ± 10.6 ml/min (n = 22), whereas mean urea clearance was 27.1 ± 5.1 ml/min (n = 26). Folic acid and P-5′-P removal rates were 27.0 ± 34.2 and 3.4 ± 2.0 nmol/h, corresponding to mean daily losses of nearly 650 and 80 nmol/day respectively. Conclusion: Significant losses of folic acid and P-5′-P (and most likely of other hydrosoluble vitamins) occur during CRRT. Considering that stores of most hydrosoluble vitamins are relatively low in critically ill patients, supplementation should be provided to patients treated similarly.

The influence of moderate hypoalbuminaemia on the renal metabolism and dynamics of furosemide in the rabbit

1 The present study aimed to investigate the influence of hypoalbuminaemia on the pharmacokinetics and pharmacodynamics of furosemide. Hypoalbuminaemia was produced by repeated plasmapheresis, to attain plasma albumin concentrations of 21.6 ± 0.9 g l−1, compared with 33.0 ± 0.6 g 1−1 in controls (P < 0.001). The per cent of bound furosemide in hypoalbuminaemic rabbits (90.8 ± 0.7%) was lower than that in control rabbits (97.4 ± 0.5%, P < 0.001). The kinetics of intravenous furosemide (2.5 mg kg−1) were studied in control (n = 6) and hypoalbuminaemic rabbits (n = 6). 2 To assess the effect of hypoalbuminaemia on extrarenal clearance of furosemide, functional anephria was induced by ligating the renal pedicles of 12 rabbits, which were segregated in two groups, with and without hypoalbuminaemia. 3 In the control group, total, urinary and metabolic clearances of furosemide were 11.8 ± 1.0, 5.0 ± 0.4 and 6.8 ± 0.6 ml min−1 kg−1, respectively. Compared with control rabbits, in hypoalbuminaemic rabbits, total clearance of furosemide increased by 40% (P < 0.001), result of the enhancement of furosemide metabolic clearance (Clm) from 5 to 10 ml min−1 kg−1 (P < 0.01). In hypoalbuminaemic rabbits, urinary excretion of furosemide was reduced by 26% (2451 ± 115 vs 1818 ± 134 μg h−1, P < 0.01). In anephric rabbits, furosemide total clearance was 1.77 ± 0.12 ml min−1 kg−1, value not affected by hypoalbuminaemia, confirming that the increase in Clm induced by hypoalbuminaemia occurs in the kidneys. 4 Compared with controls, in hypoalbuminaemic rabbits, the rate of urinary excretion (142 ± 9 vs 74 ± 8 ml h−1, P < 0.001) and the rate of excretion of sodium (18.6 ± 0.9 vs 9.9 ± 0.9 mmol h−1, P < 0.001) were very much reduced. However, the dose‐response curves were not different. 5 In conclusion, hypoalbuminaemia is associated with an increase in renal metabolic clearance of furosemide, possibly because of the increase in furosemide unbound concentration, and a decrease in the diuretic/natriuretic effect of furosemide, secondary to a reduction in furosemide tubular secretion. Thus, albumin facilitates the renal secretion of organic anions but not their metabolism.

Effects of the vasopeptidase inhibitor omapatrilat on cardiac endogenous kinins in rats with acute myocardial infarction.

The purposes of this study were to evaluate and to compare the effects of simultaneous angiotensin-converting enzyme (ACE) and neutral endopeptidase 24.11 (NEP) inhibition by the vasopeptidase inhibitor omapatrilat (1 mg. kg(-1). day(-1)) with those of the selective ACE inhibitor enalapril (1 mg. kg(-1). day(-1)) on survival, cardiac hemodynamics, and bradykinin (BK) and des-Arg(9)-BK levels in cardiac tissues 24 h after myocardial infarction (MI) in rats. The effect of the co-administration of both B(1) and B(2) kinin receptor antagonists (2.5 mg. kg(-1). day(-1) each) with metallopeptidase inhibitors was also evaluated. The pharmacological treatments were infused subcutaneously using micro-osmotic pumps for 5 days starting 4 days before the ligation of the left coronary artery. Immunoreactive kinins were quantified by highly sensitive and specific competitive enzyme immunoassays. The post-MI mortality of untreated rats with a large MI was high; 74% of rats dying prior to the hemodynamic study. Mortality in the other MI groups was not significantly different from that of the untreated MI rats. Cardiac BK levels were not significantly different in the MI vehicle-treated group compared with the sham-operated rats. Both omapatrilat and enalapril treatments of MI rats significantly increased cardiac BK concentrations compared with the sham-operated group (P < 0.05). However, cardiac BK levels were significantly increased only in the MI omapatrilat-treated rats compared with the MI vehicle-treated group (P < 0.01). Cardiac des-Arg(9)-BK concentrations were not significantly modified by MI, and MI with omapatrilat or enalapril treatment compared with the sham-operated group. The co-administration of both kinin receptor antagonists with MI omapatrilat- and enalapril-treated rats had no significant effect on cardiac BK and des-Arg(9)-BK levels. Thus, the significant increase of cardiac BK concentrations by omapatrilat could be related to a biochemical or a cardiac hemodynamic parameter on early (24 h) post-MI state.

Influence of phenobarbital pretreatment on methoxyflurane and sodium fluoride nephropathy in Fischer 344 rats

Abstract Adult male Fischer 344 rats were used to investigate the effect of phenobarbital on methoxyflurane- and sodium fluoride-induced nephropathy. Pretreatment consisted of the ip administration of phenobarbital sodium at a dose of 50 mg/kg/day for 5 days; control animals were given saline. Pretreated animals were exposed to anesthetic concentrations of methoxyflurane during a period of 2 or 4 hr, whereas other pretreated animals were exposed only to oxygen, the methoxyflurane carrier gas. For comparative purposes, other pretreated animals received sodium fluoride in saline at doses of 0, 4.2 and 8.4 mg/300g. The results show that phenobarbital pretreatment enhances the nephrotoxicity of methoxy-flurance as evidenced by a significant interaction between phenobarbital and methoxyflurane on plasma concentrations of sodium and potassium, urinary volume, urinary excretion of urea, and urinary concentration test. In contrast, the nephrotoxicity of sodium fluoride was not affected by phenobarbital. These results provide good evidence that the urinary concentration test is a reliable monitor of the potentiating effect of phenobarbital on methoxyflurane nephrotoxicity.

Transient middle cerebral artery occlusion influence on systemic oxygen homeostasis and erythropoiesis in Wistar rats.

Background and Purpose— Systemic hypoxia is a common complication in stroke patients and may exacerbate ischemic brain damage. Expression of the hypoxia-inducible cytokine erythropoietin (Epo) is upregulated in the brain in both stroke patients and in animal stroke models and exerts local neuroprotective effects in the ischemic brain. Epo is also well known to stimulate red blood cell (RBC) production. The purpose of the present study was to evaluate whether poststroke systemic hypoxia is present in the rat model and whether it is associated with increased peripheral Epo and RBC production. Methods— Wistar rats underwent 1-hour transient middle cerebral artery occlusion (MCAO) under mechanical ventilation, followed by reperfusion without further ventilation. Groups of MCAO and sham-operated animals were evaluated at extended times after reperfusion for assessment of arterial blood gases, plasma Epo, and complete blood count. Results— Arterial oxygen saturation was significantly lower in the infarct group between 6 and 24 hours after reperfusion (P =0.0005), and plasma Epo levels were increased 6 hours after reperfusion (P <0.05). RBC counts and hematocrit were transiently increased 2 to 7 days after reperfusion in animals with MCAO compared with sham. Maximal increases were seen at day 7 (22% and 16% increases of RBC count and hematocrit, respectively; P <0.001). In contrast, the white blood cell counts in animals with MCAO decreased by >30% in the same time period. Conclusions— Plasma Epo levels, RBC counts, and hematocrit are all increased in response to systemic hypoxia after cerebral ischemia in rats.