Blood flow rate and energy charge in the isolated perfused canine liver

Background. Liver viability depends on blood flow rate, which varies among isolated perfused livers used in different studies. We aimed to identify the minimal blood flow capable of keeping the energy charge compatible with liver viability. Materials and methods. Isolated canine livers were assigned to different groups (n = 4) with blood flow rates of 0.5 (Group I), 1.0 (Group II), and 1.5 ml/g/min (Group III). Blood gases, hematocrit, and glucose were measured over 180 min. Nucleotides, serum osmolarity, and electrolytes were also measured. Morphological changes were recorded at the end of each experiment. Results. Acid-base balance was better in livers from Group III. Electrolytes, osmolarity, hematocrit, and glucose showed no differences. Higher energy charges correlated with higher blood flow rates. On histopathology, there was evidence of more hydrostatic pressure-related changes in Group III, with no difference in necrosis or inflammatory-related alterations. Conclusions. (1) Energy charge correlates strongly with blood flow rate. (2) A rate of 1.5 ml/g/min allows for a better electrolyte, osmolarity, and acid-base balance. (3) Morphological analysis is not a sensitive predictor of organ viability as assessed by energetic potential. (4) The minimal blood flow rate required to attain an energy charge above 0.75 is 1.33 ml/g/min.

Mechanisms involved in the cardiovascular alterations immediately after spinal cord injury

The early cardiovascular effects resulting from an acute spinal cord injury (SCI) produced by a contusion procedure at T5-T6 were evaluated in anaesthetized rats. The mean arterial pressure (MAP) and heart rate (HR) were measured during one hour after the injury. A marked decrease in MAP and HR was observed immediately after injury, followed by an abrupt increase in MAP. These changes were observed between 3 and 9 min and the basal values were recovered after 20 min. Fall in the MAP and HR and increase in MAP induced by SCI were abolished by atropine. The interruption of the parasympathetic outflow by vagotomy also significantly diminished the fall and increase in MAP and the fall in HR. Likewise, pre-treatment with nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME) completely abolished the effects produced by SCI. These data suggest that after SCI the decrement in MAP and HR was probably due to acetylcholine release from parasympathetic fibers and NO from endothelial source probably by a cholinergic stimulation. Additionally, the MAP increase observed was probably due to a reflex compensatory vasoconstriction.

Early changes in nitric oxide synthase activity in atrial intramural arteries following experimental spinal cord injury in rats

Previously, we have shown that immediately after an experimental spinal cord injury (SCI) in anaesthetized rats, there is a large fall in mean arterial pressure (MAP) and heart rate (HR), followed by an abrupt increase in MAP. To evaluate the participation of nitric oxide (NO), we evaluated the activity of nitric oxide synthase (NOS) using Nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase histochemistry in sections of atria at several post-injury time-intervals. Staining increased at 3 min, reached a maximum at 9 min and diminished 30 min after injury. Pretreatment with atropine prevented changes in MAP, HR and NADPH-d staining suggesting that such modifications result from an increased vagal stimulation. In conclusion, the NOS activity is transiently elevated in the atrial intramural arteries of rats subjected to an SCI.

A model of suture-induced urolithiasis with urographic control in the bladder of the rat

The characteristics of a model of urolithiasis in the bladder of male Wistar rats were evaluated. Two techniques were compared: one knot of suture material through the bladder wall, or 15-throw knots inside the bladder. Rats were randomly assigned to one of six groups, according to the technique and suture material used (polyester, silk, or chromic catgut). An excretory urogram was performed at days 30, 60, and 90. At the moment of positive radiographic diagnosis, animals were sacrificed and stones were obtained. All rats were sacrificed at day 90 regardless of the x-ray results. Variables evaluated were average days to a positive urogram, average weight of all uroliths, and percentage of animals developing urolithiasis throughout the study. There were no statistical differences between groups for the average weight of stones, which ranged from 0.008 to 1.502 g for individual cases. All three materials were more lithogenic with the 15-throw knot inside technique. No significant differences were detected for lithogenesis criteria between suture materials. X-ray dispersion spectroscopy evidenced calcium phosphate composition of two stones from chromic catgut, and magnesium phosphate composition of two stones from chromic catgut, two from silk, and two from polyester. Neo-epithelization over the suture was confirmed microscopically in bladders with the one-throw technique. We conclude that (1) this is an effective model of urolithiasis, with predictability in time, composition, and amount of stone formation; (2) the presence of more suture material inside the bladder is more lithogenic; and (3) excretory urograms are highly sensitive and specific for the noninvasive diagnosis of bladder urolithiasis.

The protective action of amlodipine on cardiac negative inotropism caused by prolonged incubation in vitro

The mechanism of the antihypertensive action of the 1,4-dihydropyridine Ca2+ antagonist amlodipine was studied in isolated ventricular strips and aortic rings from Wistar rats after oral treatment with amlodipine 15 mg/kg/day for one week. The contractions evoked by electrical stimulation of isolated strips from right ventricles pretreated with amlodipine (5 nM) were unaffected during the first hour after mounting, but they decreased in magnitude after prolonged incubation (4 hr). However, the decrease in response of these preparations after prolonged incubation was less than that observed in strips prepared from untreated rats. A negative inotropic effect of amlodipine was observed at concentrations higher than 300 nM. In the presence of lower concentrations of amlodipine (5 nM-30 nM) after prolonged incubation, the contractions of ventricular strips were significantly more sustained than in the absence of amlodipine. Likewise, the decrease in contractility evoked by increasing the stimulation frequency from 1 to 3 Hz was reduced in amlodipine treated rats. The recovery of contractility was improved when stimulation frequency was returned to 1 Hz. On the other hand, when rat ventricular strips pretreated with amlodipine (5 nM) were exposed to isoprenaline (3 microM), the contractions evoked by isoprenaline were enhanced. The isoprenaline effect was not altered with 300 nM amlodipine, but with 3 microM became weak and was significantly lower than in strips treated with isoprenaline alone. In addition, treatment with amlodipine produced a marked decrease in the contractions evoked by 100 mM KCl solution in isolated aortic rings when compared to untreated rats. This inhibition was produced in a time-dependent manner with an IC50 equal to 30 and 3 nM after 2 and 45 min of contraction, respectively. Ex vivo results show that amlodipine treatment decreased aortic contractility without producing a negative inotropic effect although there was an occupation of cardiac Ca2+ channels. These results suggest that a protective effect of amlodipine on cardiac negative inotropism is produced by prolonged incubation in vitro.

Bovine babesiosis: pathogenicity and heterologous species immunity of tick-borne Babesia bovis and B bigemina infections

A total of 22 nonsplenectomized Hereford, Holstein-Friesian, and cross-bred 18-month-old cattle were used to assess the degree of protection conferred by previous infection with Babesia bovis or B bigemina against infection and disease from tick-borne challenge exposure with the heterologous species. Prior infection with B bigemina or B bovis did not significantly (P less than 0.05) reduce the susceptibility of cattle to tick-borne infection and disease caused by the heterologous species. Carrier infections were not activated during heterologous species challenge exposure, nor was the severity of the challenge-exposure infection aggravated. Immunologic cross reactivity in the indirect fluorescent antibody test was restricted to the period during and shortly after recovery. Homologous indirect fluorescent antibody titers persisted long after primary infections with B bovis, but gradually declined in B bigemina-immune cattle. Babesia bovis infections caused severe reactions characterized by high fever, pancytopenia, and death of 9 of 15 infected cattle. Total serum bilirubin and urea nitrogen values increased markedly within 24 hours preceding death and were often accompanied by clinical signs of CNS involvement (incoordination, opisthotonos, and paddling). Microscopic lesions were restricted largely to kidney, CNS, and liver parenchyma and were characterized by vascular congestion and aggregation of infected erythrocytes in small vessels. Babesia bigemina, in contrast, caused only mild fever and anemia despite prolonged parasitemia and marked thrombocytopenia. The absence of significant (P less than 0.05) heterologous species immunity indicated that protection of cattle from these 2 babesial parasites will require specific immunization against each species.