Effects of changes in plasma volume on fatal rhabdomyolysis in the rat induced by glycerol injections

Evaluation of Myoglobin Clearance during Continuous Hemofiltration in a Swine Model of Acute Renal Failure

Rhabdomyolysis is characterized by extensive damage of striated muscle, while the major complication of this disease is the development of acute myoglobinuric renal failure. Although first described more than five decades ago very little has changed with regard to the management of this entity as conventional hemodialysis has not been shown to effect myoglobin elimination. However, continuous arteriovenous hemofiltration (CAVH) offers an alternative to conventional hemodialysis as this procedure is more effective particularly for removing larger molecular weight substances such as myoglobin. We studied the effect of CAVH on myoglobin clearance in an animal model of acute myoglobinuric renal failure. Swine (n=6) were given 4 grams of equine myoglobin intravenously and underwent the CAVH procedure for six hours each. Once the filtering process was initiated there was a rapid and sustained production of ultrafiltrate. The clearance of myoglobin via the hemofilter was 2.05 ± 1.48 L/day. The amount of myoglobin excreted in the ultrafiltrate over the six hour filtering period was 410 ± 234 mg which accounts for 10.27 ± 5.85 percent of the administered dose. Based on these findings, it appears that the hemofiltration system is a viable option for the removal of myoglobin from the systemic circulation.

Myoglobin Clearance during Continuous Veno-Venous Hemofiltration with or without Dialysis

The management of acute myoglobinuric renal failure, the major complication of rhab-domyolysis, continues to be a treatment dilemma for the clinician as limited therapeutic options are available. Previously, we have demonstrated that continuous arteriovenous hemofiltration (CAVH) is an effective technique for removing myoglobin in an animal model. In the present study, swine were administered four grams of equine myoglobin intravenously and underwent the continuous veno-venous hemofiltration (CVVH) procedure for six hours each. Animals were studied in each of the following groups: CVVH at a pump rate 100 ml/minute, CVVH at a pump rate 200 ml/minute and CVVH at a pump rate 100 ml/minute plus dialysis at a dialysate flow rate of one Liter/h. Once the filtering process was initiated there was a rapid and sustained production of ultrafiltrate in all groups. The amount of myoglobin excreted in the ultrafiltrate over the six-hour filtering period was 688, 948 and 570 mg which corresponded to 17, 24 and 14 percent of the administered dose, respectively, for the three treatments. In comparison to previous CAVH experiments, CVVH removed more circulating myoglobin and the addition of the dialysis component did not appear to improve removal. Based on these findings, it appears that the CVVH hemofiltration system is a viable option for the removal of systemic myoglobin.

Glycerol-induced augmentation of sensitivity to endotoxin in rats

Combined sepsis and rhabdomyolysis result in a mortality rate much higher than that caused by each process alone. An analogous rat model is obtained by simultaneous i.p. administration of a nonlethal dose of lipopolysaccharide (LPS 0.025 mg/100 g) and a nonlethal i.m. injection of glycerol (1 ml/100 g). The aim of this study was to determine the factors contributing to the high mortality rate in this rat model. The factors examined include: Dehydration, plasma volume expansion, 'immunization' to glycerol, induction of LPS tolerance and the effect of free radicals formed in this model. Neither dehydration nor volume expansion affected mortality. 'Immunization' with glycerol was also not effective. In contradistinction, tolerance to LPS achieved by a daily injection with gradual increasing doses of LPS (from 0.05 mg/100 g to 1 mg/100 g) for 6 days reduced the mortality rate by 60% (P < 0.001). Moreover, decreasing free radical activity using the natural antioxidant (NAO) (5 mg/100 g) reduced mortality rates by 50%. A different antioxidant, dimethylthiourea (DMTU) (50 mg/100 g) failed to reduce mortality rates. This study suggests that the synergism between glycerol and LPS is apparently due to an increase in the rats' sensitivity to endotoxin following glycerol injection. However, endotoxin apparently does not enhance sensitivity to glycerol in the rat. The new antioxidant NAO significantly reduced the high mortality rate.

Evidence against oxidant injury and endotoxin underlying glycerol-induced fatal rhabdomyolysis in rats

Rhabdomyolysis in experimental animals and in man may be fatal. The mechanism of action causing death in man and in the experimental model of laboratory animals injected with glycerol in a dose causing fatal rhabdomyolysis is unknown. The aim of this study was to examine two possible causes of death following glycerol injection (0.5-2 ml/100 g) to the leg muscle of rats following a period of water deprivation (24-72 h). The first factor examined was free radical formation, via the administration of various antioxidants such as natural antioxidant (NAO - 5 mg/100 g), vitamin E (0.2 mg/100 g each day for 7 days), dimethylthiourea (DMTU - 50 mg/100 g) and superoxide dismutase (SOD - 0.8 mg/100 g). The second factor was a high blood endotoxin level due to the glycerol injection. This possibility was examined by glycerol injection to rats that had developed endotoxin tolerance. The low survival rate (0-30%) of rats receiving a glycerol injection following preventive treatment with antioxidants as well as rats which had developed endotoxin tolerance (0-40%), excludes the possibility that the cause of death in the glycerol model resulting in fatal rhabdomyolysis is due to free radical formation or to a high and unneutralized blood level of endotoxin.