The viability of hemoglobin-free perfused rat liver was examined with respect to several liver functions and to the intactness of subcellular structures under electron microscopic observation. Provided that rat livers were perfused with the oxygenated buffer solution at a flow rate between 3 and 3.5 ml/min per g of liver, all the biochemical parameters measured in the perfused liver system, i.e. the rates of glucose, pyruvate, and lactate production, the rate of oxygen consumption and the tissue contents of adenine nucleotides, were similar to those observed with perfusion systems containing erythrocytes or albumin. The perfused liver showed a sensitive response to norepinephrine, involving a reduction of pyridine nucleotides and enhancements of glucose production and oxygen consumption. On electron microscopic examination, changes in hepatic-structure indicative of hypoxic injury particularly vacuolar degeneration and mitochondrial swelling, were not detected in the liver after 70 min of perfusion; the fact that the fine structure of the hepatocyte was preserved in all parts of the organ confirmed that the supply of oxygen to the perfused liver was sufficient under the conditions employed. From viewpoint of the generally accepted criteria for the viability of perfused liver, therefore, the results confirmed that the perfusion of liver with a hemoglobin- and albumin-free medium is a convenient and reliable tool for biochemical investigation of the reactions occurring in whole liver.

The role of the cellular redox state in the hormonal stimulation of gluconeogenesis was studied in hemoglobin-free perfused rat liver, by fluorimetric measurement of the redox states of intracellular pyridine nucleotides. The maximum rate of glucose production from lactate/pyruvate mixture was observed with a lactate/pyruvate ratio of 10/1, which corresponds to the ratio observed in vivo. Increased reduction of pyridine nucleotides on infusion of ethanol or octanoate was associated with an increased production of glucose from pyruvate, whereas glucose production from lactate decreased. Stimulation of gluconeogenesis from lactate by glucagon was affected by the lactate/pyruvate ratio; a decrease of the lactate/pyruvate ratio resulted in a decrease of the efficacy of glucagon. Stimulation by glucagon of glucose production from pyruvate was abolished during octanoate infusion, although it was still observable during ethanol infusion. In contrast to glucagon, the stimulatory effect of norepinephrine on gluconeogenesis was unaffected by the ratio of lactate to pyruvate. Norepinephrine in the presence of octanoate and ethanol still induced stimulation of glucose production from lactate and pyruvate, which was always accompanied by a transient reduction of pyridine nucleotides. The results demonstrate that the regeneration of NADH in the cytosol is one of the regulatory factors in gluconeogenesis, and that the effects of glucagon and norepinephrine on gluconeogenesis and on the redox state of pyridine nucleotides are not identical.

Objective To determine the influence of anatomical features of the distal femur on the proximodistal patellar position and compare the proximodistal patellar position between dogs with and without medial patellar luxation (MPL). Study design Retrospective case series (n = 71). Methods Mediolateral-view radiographs of clinical cases of dogs weighing less than 15 kg were obtained. The stifle joint angle, patellar ligament length, patellar length, size of the femoral condyle, trochlear length, and trochlear angle were measured and included in multiple linear regression analyses to ascertain their effects on the proximodistal patellar position. Radiographs were divided into MPL and control groups. The effects of MPL on the proximodistal patellar position and morphological factors were also examined. Results The final model for the proximodistal patellar position revealed that the patella became distal as the ratio of the patellar ligament length to patellar length decreased, the trochlear angle relative to the femur increased, the trochlear length relative to the patellar length increased, or the trochlear length relative to the femoral condyle width decreased. The proximodistal patellar position in the MPL group was not significantly different from that in the control group despite the trend towards a distally positioned patella (p = 0.073). The MPL group showed a significantly shorter trochlea (p<0.001) and greater trochlear angle relative to the femur (p = 0.029) than the control group. Conclusion The proximodistal patellar position depends on multiple factors, and its determination based on PLL/PL alone may not be appropriate. Dogs with MPL did not have a proximally positioned patella compared with dogs without MPL. Although hindlimbs with MPL had a shorter trochlea than those without patellar luxation, this difference did not appear to be sufficient to displace the patellar position proximally in small dogs, possibly compensated by increased trochlear angle relative to the femur.

Objective The aim of the study was to determine the changes in biomechanical characteristics following tibial plateau levelling osteotomy (TPLO) using simulated manual tests. Study Design Twenty-one stifles from healthy Beagle dogs that had undergone TPLO or had not (control) were first tested in the intact form, and then the cranial cruciate ligament (CrCL) was transected in each to provide four test situations: control-intact, control-CrCL-transected, TPLO-intact and TPLO-CrCL-transected. The stifles were then analysed using a robotic joint biomechanical testing system. The craniocaudal drawer, axial rotation and proximal compression tests were applied. Results The craniocaudal displacement during the drawer test was not significantly different between the control-intact and TPLO-intact. However, the displacement was significantly greater in the TPLO-CrCL-transected than in the control-intact. In the axial rotation test, the internal–external (IE) rotation was significantly greater in the TPLO-intact than in the control-intact. Similarly, the IE rotation was significantly greater in the TPLO-CrCL-transected than in the control-CrCL-transected. In the proximal compression test, craniocaudal displacement was not significantly different among the control-intact, TPLO-intact and TPLO-CrCL-transected. Conclusion These findings suggest that TPLO influences the tension of the collateral ligaments and might generate laxity of the tibiofemoral joint. Instability after the osteotomy might be associated with the progression of osteoarthritis.

The effects of calcium ions on the activation of gluconeogenesis by norepinephrine were studied in the perfused rat liver. The norepinephrine-mediated enhancement of gluconeogenesis was accompanied by a transient increase in the reduction level of pyridine nucleotides. There was a positive correlation between the increases in the rate of glucose production and the reduction level of pyridine nucleotides induced by norepinephrine. These changes were "dose-dependent" with respect to the norepinephrine concentration from 5 nM to 1 muM and were mimicked by phenylephrine. The omission of calcium from the perfusate did not modify the basal rate of gluconeogenesis from lactate and pyruvate or the increased rate of glucose production induced by glucagon and isoproterenol. The extents of the responses to norepinephrine and phenylephrine, however, were decreased markedly in liver perfused with a calcium-free medium and/or with phentolamine. Infusion of calcium into the calcium-deficient liver caused an abrupt elevation of glucose production together with a transient reduction of pyridine nucleotides, and the original extent of the response to norepinephrine was recovered. The data presented provide evidence indicating that stimulation of gluconeogenesis by norepinephrine is mediated through an alpha-adrenergic and calcium-dependent mechanism in which redox changes of mitochondrial pyridine nucleotides are involved.