M. Patricia Lange

Hepatic metabolic response to injury and sepsis

BACKGROUND Experimental reports have indicated that hepatic oxidative and synthetic metabolism may become depressed in sepsis. Because the mechanism of infection-related liver dysfunction has not been established, further study of these functional alterations could contribute to the therapeutic management of septic organ failure syndromes. However, recently controversy has arisen over the existence of these derangements that must be reconciled before further progress in this field can be made. METHODS Splanchnic balance studies for the measurement of glucose output and oxygen consumption were used to assess hepatic function in fasted normal volunteers (n = 18), injured patients (n = 10), and patients with sepsis (n = 18). The livers contribution to splanchnic metabolism was estimated from a comparison of splanchnic oxygen utilization in response to increases in the liver-specific process of glucogenesis. In addition, in vivo liver albumin production was determined by using the [14C] carbonate technique. RESULTS Glucose output after injury and sepsis was increased by 12.8% and 76.6%, respectively, compared with controls. On the basis of substrate balance studies, gluconeogenesis was estimated to account for 46%, 87%, and 93%, respectively, of splanchnic glucose output in each of the three groups. In patients with sepsis glucose output was also noted to be linearly related to regional oxygen consumption, indicating that these processes were coupled and increases in the respiratory activity of the splanchnic cellular mass could be accounted for by increases in new glucose output and gluconeogenic substrate clearance. The mean albumin synthetic rate increased during injury and sepsis by 22% and 29%, respectively, compared with normal volunteers. CONCLUSIONS These studies cast doubt on the commonly held notion that tissue respiratory dysfunction may occur during sepsis. On the contrary, hepatic function is accelerated during hyperdynamic sepsis, and evidence indicating oxidative or synthetic functional depression is lacking.

Altered Immunologic Function and Nitrogen Metabolism associated with Depression of Plasma Growth Hormone

The specific role of endogenous growth hormone in regulating nitrogen metabolism during surgical stress and infection remains unclear. We have studied splanchnic amino acid uptake and plasma concentrations in patient groups exhibiting growth hormone hypersecretion or relative growth hormone depression in response to stress. Splanchnic amino acid uptake was similar in both groups although plasma levels were significantly higher in the presence of depressed growth hormone production suggesting increased net peripheral proteolysis. In association with this latter observation. T lymphocyte subset analysis revealed a greater incidence of depressed helper to suppressor cell ratios in the presence of depressed growth hormone suggesting a greater impairment of cellular immunity.

Factors affecting secretory protein production in primary cultures of rat hepatocytes

Abstract Previous studies suggest that protein synthesis in the liver may be influenced by alterations in hepatic proteolysis and gluconeogenesis. Since proteolysis and gluconeogenesis are accelerated in acute stress states (especially when associated with nutrient deprivation), these alterations may substantially affect hepatic protein synthesis, the integrity of which is important for host survival. In the present study, we have investigated albumin secretion and glucose production in primary cultures of rat hepatocytes in response to nutrient-limiting conditions, including amino acid depletion, proteolysis inhibition, and augmented gluconeogenesis. In nonlimiting nutrient culture medium containing 10 times the normal plasma amino acid concentrations, hepatocytes produced 8.05 ± 1.62 μg/plate-hr of albumin. Short-term (5 hr) inhibition of cellular protein degradation with the lysosomal protease inhibitor leupeptin did not influence albumin production, but caused a profound reduction (17-41%) when amino acid supply was reduced to the physiologic range (1.5-0.5 times, respectively). This indicates the need for active proteolysis for the maintenance of secretory protein production during nutrient limitation. Similarly, leupeptin inhibited glucose production by 22-30% at physiologic (1.5 times and 0.5 times, respectively) amino acid concentrations. Additionally, hepatocyte glucose production could be augmented 168% by epinephrine (2 μM) in 10 times medium, but this response was markedly depressed by leupeptin. Similar catecholamine-mediated effects, but of a smaller magnitude, were noted at lower medium amino acid concentrations. These findings indicate that hepatocyte albumin and glucose production are associated with the common factor of active cellular proteolysis, probably through the regulation of amino acid supply. However, protein synthesis exhibits a higher priority, since stimulated hepatocyte glucose production did not substantially alter albumin secretion.

Development of a percutaneous fiberoptic hepatic venous localization catheter.

OBJECTIVE To develop a liver-specific biosensor system/catheter assembly that can be used to localize and cannulate the hepatic venous system without the need for fluoroscopic imaging. This would permit the bedside placement of a hepatic venous catheter for monitoring purposes without radiographic guidance. DESIGN Experimental, in vitro. STUDY SETTING Experimental laboratory at a university center. SUBJECT This was a simulation study to evaluate the ability of a cardiovascular monitoring catheter mounted with a liver-specific biosensor to anatomically identify a side arm tributary. The experimental system used for this study mimics the hepatic vein draining into the inferior vena cava and allows its localization without the need for assisted imaging. The biosensor design and catheter/sensor assembly function were studied in this in vitro model. INTERVENTIONS A liver-specific biosensor was developed by housing a homogeneous affinity fluorescence assay system sensitive to galactose in a microdialysis hollow fiber receptacle. A polyvinyl chloride tube containing a side arm was constructed to mimic the confluence of a venous tributary (i.e., the hepatic vein) with a major vascular channel (i.e., the vena cava). In this simulation, the side arm was continuously perfused with a liver-sensitive analyte (galactose) and the main channel was perfused with galactose-free buffer. A cardiovascular catheter containing a fiberoptic waveguide mounted with a galactose-sensitive fluorescent probe was advanced along the main conduit to assess its ability to identify the location of the galactose side arm infusion site. MEASUREMENTS AND MAIN RESULTS The response of the fiberoptic sensor to different galactose concentrations was assessed and found to be almost linear over the concentration range of 0 to 2 mM, which encompasses the expected utilization range of this system. The variability in identifying the galactose infusion point (simulated hepatic vein) in a 15-cm conduit was 1.7 to 2.8 mm, or 1.1% to 1.9%. CONCLUSIONS The construction of a catheter/sensor system with the ability to provide accurate spatial/anatomical localization data for the hepatic venous system is feasible. This assembly will eliminate the need for ancillary imaging systems for catheter/sensor delivery to an individual organ system and potentially can be positioned at the bedside in a fashion similar to the pulmonary artery flotation catheter.

A homogeneous affinity fluorescence assay system for galactose monitoring

Abstract Since the systemic venous-hepatic venous galactose gradient is normally quite large, the ability to detect different blood galactose concentrations in vivo would provide a mechanism for anatomic localization of the hepatic venous system. Furthermore, the development of a catheter assembly mounted with a galactose-sensitive biosensor would provide a technique for cannulating this organ system entirely using sensor guidance. In this report we describe a homogeneous affinity fluorescence assay system which can be contained in a dialysis hollow fiber for continuous galactose monitoring. The principle of this assay is based upon competition of freely permeable galactose for the specific binding interactions between a fluorescently labeled polysaccharide and lectin reagent pair. This competetive energy-transfer assay exhibits good sensitivity over a physiologically relevant galactose concentration range (0–2 mM), an acceptable response time (

Prototype for an organ system (liver) localization cardiovascular catheter

This study describes the function and potential clinical utility of a sensor which can serve as a guidance mechanism allowing for the selective cannulation of the hepatic venous system without the need for additional imaging technology. The sensor is based upon a homogeneous affinity fluorescence assay system utilizing the lectin Ricinus cummunis agglutinin I and covalently linked to the fluorophol Alexa 488 and its conjugate polydextran labeled with rhodamine and lactose. The affinity between these two macromolecules is sensitive to ambient galactose concentration which exists as a steep gradient at the hepatic venous/vena caval junction allowing this anatomic region to be discriminated from irrelevant regions. This sensor system permits venous access for additional monitoring approaches such as venous oximetry.

Hemodynamic benefits of verapamil after aortic reconstruction

Because of the high incidence of coronary artery disease (CAD) in patients undergoing aortic surgery, and because myocardial oxygen consumption is proportional to blood pressure x heart rate (HR) (pressure-rate product), it is important to prevent increases in these parameters postoperatively. The effect of verapamil, a calcium channel antagonist, on these parameters was evaluated in 30 patients undergoing abdominal aortic reconstruction. Postoperatively HR increased 27% in 19 patients without CAD and 47% in 11 patients with CAD. Pressure-rate product (blood pressure x HR) increased 17% and 31% in these two groups, respectively. Verapamil was able to reduce postoperative HR by 3% in patients without CAD and by 13% in patients with CAD. Verapamil reduced pressure-rate product 8% and 18%, respectively, in the two groups. These reductions were statistically significant in patients with CAD and occurred without reductions in cardiac output or left ventricular ejection fraction. Thus the postoperative increases in myocardial oxygen demand appeared to be primarily related to increased HR after aortic surgery, and these were reduced by verapamil without impairing blood flow or cardiac function.