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Biomedical subjects

M G Clemens

Publications and source records attributed to M G Clemens.

90 records · Page 5Linked to original sources
PubMed1984

Insulin resistance and depressed gluconeogenic capability during early hyperglycemic sepsis.

The present study was performed to determine whether insulin resistance, independent of the prevailing hormonal milieu, occurs in the liver during sepsis. To determine this, sepsis was produced in rats by cecal ligation and puncture (CLP). Six hours later, when the rats were in the early hypermetabolic phase of sepsis, the livers were isolated and perfused with Krebs-HCO3 buffer using a nonrecirculating system. The effects of various concentrations of insulin on the gluconeogenic response to lactate and phenylephrine stimulation were determined. In the absence of insulin and phenylephrine, there was no difference in the rates of glucose production from lactate between septic and sham-operated rats. The gluconeogenic response to phenylephrine stimulation was, however, significantly depressed in the livers from septic rats. Addition of 50 microU insulin/ml resulted in an inhibition of the phenylephrine-stimulated glucose release from livers from sham-operated rats. This inhibition was maximal at 100 microU insulin/ml. In contrast, significant inhibition of phenylephrine-stimulated glucose release from livers from septic rats was only observed in the presence of 2,000 microU insulin/ml. These results demonstrate that even during the early, hypermetabolic phase of sepsis, depressed hormonally stimulated hepatic gluconeogenic capability occurs. In addition, livers from septic rats exhibited a resistance to the effects of insulin on gluconeogenesis. This resistance may account, at least in part, for accelerated gluconeogenesis in spite of hyperinsulinemia in early sepsis.

Abdomen↗
PubMed1984

Improved mitochondrial function following ischemia and reflow by ATP-MgCl2.

To determine whether infused ATP-MgCl2 affects mitochondrial adenine nucleotide translocase (ANT) activity, free fatty acids (FFAs), and Ca2+ levels, total hepatic ischemia in rats was produced for 90 min after which blood flow was allowed to return to the liver. Immediately on reflow, the animals received intravenously 0.5 ml of either saline, ATP-MgCl2 (12.5 mumol), or dopamine (6 mg/kg). Three hours after ischemia and reflow, hepatic mitochondrial FFAs and Ca2+ levels increased; however, ATP-MgCl2 infusion significantly lowered FFAs and restored Ca2+ levels. The depressed mitochondrial ANT activity was somewhat improved but not restored by circulatory support with dopamine; however, ATP-MgCl2 infusion following ischemia restored that activity. Thus the present results suggest that the improved organ function that occurs with ATP-MgCl2 infusion following ischemia may be mediated through an improvement in ischemia-induced mitochondrial function.

Adenosine Triphosphate↗
PubMed1984

Accelerated functional recovery of isolated rat kidney with ATP-MgCl2 after warm ischemia.

Isolated rat kidneys were subjected to 45, 60, and 90 min of normothermic ischemia. Kidneys reperfused with a saline solution after ischemia had very low initial whole kidney inulin clearances (Cin), urine flow rates (V), renal perfusate flow rates (RPF), and fractional absorption of sodium values that remained depressed throughout the 110 min of reperfusion. Kidneys subjected to 45 min of warm ischemia and reperfused with a solution containing 0.3 mM ATP-MgCl2 had higher initial Cin and attained complete recovery of Cin by 75 min of perfusion. Fractional absorption of sodium and water were also improved, and RPF, V, and tissue ATP levels returned to control values after 110 min of perfusion. Kidneys subjected to 60 min of ischemia and reperfused with a solution containing 0.3 mM ATP-MgCl2 also had higher initial Cin values and attained 50% recovery of Cin after 110 min of perfusion. RPF also improved, and V reached control levels. Kidneys subjected to 90 min ischemia showed no improvement in renal function even with 2 mM ATP-MgCl2. Because, even in isolated kidneys, administration of ATP-MgCl2 after 45 and 60 min of ischemia results in an early recovery of renal function, the beneficial effects of ATP-MgCl2 are exerted directly on the kidney and are not mediated via systemic effects.

Adenosine Triphosphate↗
PubMed1983

Beneficial effects of implanted muscle tissue on pulmonary particulate retention and survival following splenectomy.

Following splenectomy (SPLY) there is increased retention in the lung of injected particulate matter and an increased mortality from sepsis in experimental animals. Since it has been shown that autotransplanted splenic tissue (AST) decreased elevated pulmonary particulate retention after SPLY and improved the survival of animals following SPLY and sepsis, we attempted to determine whether the protective effect offered by AST was specific to the spleen. To determine this, four groups of rats were studied: Group I--sham; Group II--SPLY; Group III--received 100 mg of heterotopic AST in an omental pocket after SPLY; and Group IV--received 100 mg of heterotopic muscle tissue from the abdominal wall (AMT) in an omental pocket after SPLY. Six days after the above procedure, reticuloendothelial (RES) function was evaluated. The results indicate that both AST and AMT significantly decrease the abnormal pulmonary retention of particulate matter following SPLY. However, hepatic lipid retention was greater in the AMT than the AST group. Survival following sepsis was studied in other animals from Group I, II, III, and IV. At 7 days after the original operation, the cecum was ligated and punctured (CLP) and then removed 16 hours later. The splenic-as well as muscle-implanted animals showed significantly higher survival rates than the splenectomized animals. We therefore conclude that survival after SPLY can be improved by implanting either a fragment of the spleen or the muscle in the omental pocket. Since both tissues appeared necrotic at 7 days following implantation, the decreased pulmonary particulate retention and improved survival following SPLY and sepsis appear to be due to the presence of a necrotic tissue irrespective of its origin. These results suggest that the early effect of an implanted tissue is a nonspecific stimulation of phagocytosis.

Abdominal Muscles↗
PubMed1983

Studies on the mechanism of beneficial effects of ATP-MgCl2 following hepatic ischemia.

Infusion of ATP-MgCl2 following hepatic ischemia significantly improves the survival of animals. To determine the subcellular effects of infused ATP-MgCl2 and whether such effects are mediated through vasodilatation, global hepatic ischemia in rats was produced for 90 min followed by reperfusion. The rats then received iv 0.5 ml of saline, dopamine, papaverine, or ATP-MgCl2. At various intervals following reflow, hepatic mitochondria were isolated. ADP-to-O ratio and respiratory control ratio (RCR) were significantly lower 1 h following reflow, and there was a further decrease in these parameters 3 h after reflow in mitochondria from saline-treated rats. Dopamine and papaverine treatment did not improve RCR, however, ATP-MgCl2 treatment resulted in a progressive and significantly higher ADP/O and RCR following reflow. Hepatic ATP levels in saline, dopamine, and papaverine-treated rats were found to be 50% lower 3 h following reflow, however, treatment with ATP-MgCl2 resulted in significantly higher ATP levels and energy charge. Hepatic blood flow was markedly depressed 1 h following reflow in the saline-treated rats but was significantly higher in the ATP-MgCl2 group. Three hours following reflow, hepatic blood flow decreased further in the saline-treated rats, whereas in the ATP-MgCl2-treated rats there was a progressive increase in flow. Dopamine treatment resulted in an initial restoration in flow, however, this effect was not sustained. Hepatic ultrastructure deteriorated progressively following reflow in the saline-treated rats, however, it was normal in the ATP-MgCl2-treated rats 1 h as well as 20 h following reflow. These results lead us to conclude that infused ATP-MgCl2 improves mitochondrial and cellular functions either directly or by way of long-term improvement in microcirculation but not through vasodilatation.

Adenosine Triphosphate↗
PubMed1983

Regulation of glucose production from lactate in experimental sepsis.

Gluconeogenic and oxidative capabilities with lactate as a substrate were studied in perfused livers isolated from rats in late sepsis. Glucose release in the presence of 5 mM lactate was significantly depressed in livers from septic rats. When gluconeogenesis was stimulated by phenylephrine, livers from septic rats exhibited both a decreased sensitivity and lower maximal rate of glucose release when compared with livers from sham-operated rats. Oxygen consumption (VO2) by perfused livers from septic rats was also depressed under the above conditions. The addition of lysine in concentrations greater than 0.5 mM restored glucose production in livers from septic rats to a rate not different from sham-operated controls but did not restore VO2. However, inclusion of lysine (5 mM) in the perfusate was not able to restore sensitivity to stimulation by phenylephrine in livers from septic rats. Although hepatic ATP levels were depressed in sepsis, the decrease was not sufficient to explain the decreased rates of glucose production. We conclude from these results that primary cellular defects in gluconeogenic and oxidative capabilities occur during sepsis that are independent of inadequate perfusion.

Adenosine Triphosphate↗
PubMed1983

Alterations in electron transport and cellular metabolism with shock and trauma.

A singular scheme of progressive alterations in cell function with hemorrhagic shock and ischemia has been presented. Alterations in mitochondrial function during shock and ischemia with different substrates have been described in detail. These consist of decreases in the capability of mitochondria, alterations in mitochondrial cation contents, increased mitochondrial FFAs and Ca2+ levels, and decreased adenine nucleotide translocase activity. The potential mechanisms responsible for altered mitochondrial functions during shock and the potential consequences of such alterations have been discussed. In addition, the beneficial effects of ATP-MgCl2 on mitochondrial function following shock and ischemia have been described. The experimental evidence available indicates that infused ATP-MgCl2 improves cellular and mitochondrial functions directly and by way of long-term improvement in microcirculation but not through vasodilatation. Our results with ATP-MgCl2 therefore provide for the possibility of supporting cellular and mitochondrial functions during shock or low flow conditions.

Adenine Nucleotides↗
PubMed1982

Altered hepatocellular active transport. An early change in peritonitis.

Multiple system failure is often the final result of severe infection that cannot be controlled. The changes that may occur in remote organs and cells in the early stages of sepsis and that may initiate this process have not been defined. To study this, indocyanine green (ICG) clearance, serum enzyme levels, and reticuloendothelial (RE) function were measured during various stages of sepsis, which was produced in rats by cecal ligation and puncture (CLP). The clearance of ICG decreased significantly during the early stages of sepsis (five hours after CLP) at a time when there was no change in the serum enzyme levels or RE function. Ten hours after CLP, RE function was depressed, and serum enzyme levels were elevated. Progressive changes in RE function and serum enzyme levels occurred in the late stages of sepsis (16 hours after CLP). Since unaltered hepatic adenosine triphosphate levels have been previously found, even ten hours after CLP, humoral factor(s) may be responsible for altered ICG clearance in the early stages of sepsis. Thus, hepatocellular dysfunction occurred early in the course of sepsis and was manifested by a deficit in a plasma membrane active transport process (ICG clearance). Indocyanine green clearance provided an extremely sensitive early indication of a hepatic abnormality.

Alanine Transaminase↗
PubMed1982

Hepatic gluconeogenic capability in sepsis is depressed before changes in oxidative capability.

Since plasma alanine concentrations are markedly elevated in late sepsis and alanine is an important gluconeogenic substrate, we investigated gluconeogenic activity in intra-abdominal sepsis. Sepsis in rats was produced by cecal ligation and puncture. After 17 to 21 hours (late sepsis, LS) livers from these and sham-operated rats were isolated and perfused at constant flow with Krebs buffer in the presence or absence of 10 mM alanine. Various phenylephrine (PE) concentrations were also used to measure gluconeogenic response to alpha-adrenergic stimulation. The results showed that glucose production from alanine by livers from LS rats was depressed in comparison to livers from sham rats (2.6 +/- 0.2 vs. 4.2 +/- 0.4 moles/gm/hr). Moreover, although livers from rats in LS responded to PE stimulation in a dose-dependent manner, the magnitude as well as the threshold of response was decreased in comparison to shams. In contrast to glucose production, VO2 of the sham and LS were not different under any conditions. Previous studies using lactate as a substrate, however, showed that both gluconeogenesis and oxidative responses were decreased in LS. Since hepatic gluconeogenic but not VO2 response was depressed with alanine, these results indicate that the decreased gluconeogenic capability precedes depressed oxidative capability in sepsis.

Adenosine Triphosphate↗
PubMed1982

Exacerbation of the calcium paradox with exogenous adenosine triphosphate in isolated working rat heart.

The deleterious effect of calcium withdrawal and restoration on cardiac cell membranes ('Ca-paradox') was studied using isolated, working rat heart. The optical density of the coronary sinus effluent was measured at 260 nm wavelength. The efflux of A260 material upon restoration of calcium was proportional to the duration of calcium-free perfusion, indicating graded membraneous injury. When ATP, 10(-6) to 10(-4) M, was added to the calcium-free perfusate for 30 s of calcium-free perfusion, release of A260 material increased as a logarithmic function of exogenous ATP concentration. That this exacerbating effect is produced by such low concentrations relative to intracellular amounts indicates an action of ATP on the membrane surface. It is suggested that exogenous ATP enhances calcium entry into the cell, thus contributing to calcium influx through membranes already rendered abnormally permeable from the 'Ca-paradox' mechanism.

Adenosine Triphosphate↗
PubMed1982

Impairment of reticuloendothelial function following thermal injury and its restoration with ATP-MgCl2 administration.

It is well known that reticuloendothelial system (RES) function is depressed following thermal injury. Since previous studies have shown that adenosine triphosphate (ATP)-MgCl2 restored the depressed RES function following hepatic ischemia, the present study was undertaken to determine whether administration of ATP-MgCl2 following thermal injury would have any beneficial effects on the RES function. Thermal injury in rats was produced by immersing 30% of the skin surface area in 95 degrees C H2O for 12 sec. Immediately following this, the rats received saline s.c. and 0.25 ml of ATP-MgCl2 (12.5 mumol each) or an equivalent volume of saline i.p. RES function was evaluated by measuring the intravascular clearance of 131I-triolein-labeled gelatinized test lipid emulsion. The intravascular half-time (t/2) in the burned saline-treated rats was double that of control rats at 1 and 3 days post-burn, suggesting that significant depression in RES function occurred following thermal injury. At 5 days post-burn, although the t/2 was lower than at 3 days post-burn, it was still significantly higher than controls. Administration of ATP-MgCl2 following burn injury resulted in a t/2 and phagocytic index values similar to controls, indicating the impairment of phagocytic activity of the RES function following thermal injury was reversed with treatment.

Adenosine Triphosphate↗
PubMed1982

Restoration of hepatocellular function and blood flow following hepatic ischemia with ATP-MgCl2.

The purpose of this study was to determine whether hepatocellular function is altered following hepatic ischemia and whether ATP-MgCl2 has any effect on it. To study this, total hepatic ischemia in rats was produced for 60 minutes by placing a ligature around the hepatic artery, portal vein, and the common bile duct. At the end of the ischemic period, the ligature was removed, reestablishing blood flow to the liver. The animals then received IV either 0.25 ml saline (nontreated) or 0.25 ml ATP-MgCl2 (12.5 mumoles each) (treated). Three hours following the end of ischemia, indocyanine green (ICG) clearance was determined by infusing ICG at a concentration of either 5 mg/kg body wt (low) or 25 mg/kg body wt (high). Following infusion of ICG blood samples were taken at five, six, eight, ten, 12, 15, 18, and 20 minutes thereafter to determine the ICG concentration. The clearance of ICG at low as well as at high ICG concentration was markedly depressed in the nontreated animals, suggesting that significant depression in hepatic blood flow as well as hepatocellular function was evident even three hours after ischemia. Administration of ATP-MgCl2 following hepatic ischemia, however, resulted in ICG clearance values similar to sham-operated animals when ICG was given at low as well as high concentration. Thus, ATP-MgCl2 treatment following hepatic ischemia not only seemed to restore hepatic blood flow but also active membrane transport toward normal.

Adenosine Triphosphate↗
PubMed1981

Alterations in cell function with ischemia and shock and their correction.

Progressive cell injury occurs with shock and ischemia, beginning with functional changes in the cell and cell membrane. Membrane transport and potential decrease, Na+ enters and K+ leaves cells; N+-K+ adenosine triphosphatase is activated, adenosine triphosphate (ATP) is used, and mitochondria are stimulated as increased lactate produces acidosis. Energy and cyclic adenosine monophosphate levels decrease, Ca2+ regulation is compromised, and nuclear function and protein synthesis are depressed. The cell swells, and further membrane changes occur with altered hormonal effects and mitochondrial uncoupling. Finally, lysosomes leak, intracellular and mitochondria disruption occurs, and the cell is destroyed. Based on these changes, attempts were made to directly support cell function during low-flow states. After volume replacement and vasoactive agents, other modalities, eg, substrates, membrane-stabilizing solutions, osmotic agents, and energy compounds were used. The use of ATP-MgCl2 was helpful in many experimental low-flow states, with an improvement in cell function mediated by micro-circulatory, cell membrane, or energy-recycling effects. Clinical examples of altered cell and organ function with ischemia and shock are numerous and play a critical role in the development of multiple systems failure. The potential for biochemical support and correction of these problems is now recognized. Benefits have already been achieved in myocardial preservation during cardiac operations, kidney preservation for transplantation, and circulatory and metabolic support of the injured and septic patient.

Adenosine Triphosphate↗
PubMed1981

Appearance of adenosine triphosphate in the coronary sinus effluent from isolated working rat heart in response to hypoxia.

1. A working rat heart preparation was used to study the release of adenosine-5'-triphosphate (ATP) into the coronary sinus effluent in response to hypoxia. 2. The left ventricle was set to pump against an hydrostatic pressure of 65 cm water; the left atrial filling pressure was kept constant at 10 cm water. The power output of the heart at these pressures was estimated to be approximately one half of the maximum power development. 3. Samples for ATP assay were collected (a) 30 sec before onset of hypoxia, (b) 60-90 sec after onset of hypoxia, (c) 5 min after restoration of oxygenated buffer solution. Respective concentrations of ATP were (nM +/- S.E.) 0.63 (+/- 0.18), 4.70 (+/- 0.39) and 0.63 (+/- 0.06). The total amounts of ATP detected were (p-mole/min) 5.9 (+/- 0.9), 46.1 (+/- 6.0) and 5.5 (+/- 1.2) respectively. 4. Viability of the hearts was judged to be satisfactory on the following grounds. Alterations in left atrial filling pressure produced typical Frank-Starling responses of the left ventricle. Oxygen extraction from the perfusate increased in response to increased workload. Coronary blood flow increased immediately upon introduction of hypoxic conditions and mechanical recovery from hypoxia was always complete within 5 min of restoring oxygen. 5. In view of the marked extracellular ATPase activity it is concluded that significant vasodilatory concentrations of ATP are released into the myocardial extracellular space in response to hypoxia. A scheme is proposed describing the possible role of adenine nucleotides in the local control of myocardial blood flow.

Adenosine Triphosphate↗
PubMedDate not supplied

Hypothermic machine perfusion of rat livers preserves endothelial cell function.

This study was conducted to investigate the effect of starch in the preservation solution during hypothermic machine perfusion (HMP) on endothelial cell and hepatocyte functions in an isolated perfused rat liver model. Livers isolated from male Sprague-Dawley rats were perfused with the University of Wisconsin (UW) solution (HMP + starch group); modified UW solution (starch omitted) (HMP - starch group) at 0.4 mL/min per g liver; or simply stored in the UW solution (SCS group) at 4 degrees C for 24 hours. Following preservation, livers from HMP + starch, HMP - starch, SCS, and control group (without preservation) were perfused with Krebs-Henseleit Buffer solution at 37 degrees C for 30 minutes. Samples were taken every 10 minutes during 30-minute warm perfusion to assess hepatocyte and endothelial cell function and damage. After 24 hours of hypothermic preservation and 30 minutes rewarming, livers in the HMP + starch group displayed significantly lower lactate dehydrogenase levels and higher bile production. Endothelial cell function was also improved as indicated by hyaluronic acid uptake and shorter transient time for albumin observed in a multiple indicator dilution study. Liver wet and dry ratio and histological findings confirmed reduced edema formation in the tissue of the HMP + starch group livers compared with that of the HMP - starch and SCS group livers. These results suggest that HMP with the UW solution containing starch improve endothelial cell function and induce less hepatocellular damage following 24-hour preservation compared to SCS and HMP with the starch-free UW solution. These results also suggest that oncotic support may be an important component in preserving hepatic microcirculation in HMP.

Adenosine↗
PubMedDate not supplied

Hepatic function in hypothermically stored porcine livers: comparison of hypothermic machine perfusion vs cold storage.

Hypothermic machine perfusion (HMP) has a potential to relieve the current donor liver crisis by providing an improved and extended preservation method. This study examined the effect of HMP on hepatocellular functions, using a prototype liver transporter capable of preserving livers for 24 hours. Livers obtained from adult farm pigs (28 to 32 kg body weight) were divided into three groups: fresh control, HMP, and simple cold storage (n = 4 each). A 4-hour normothermic reperfusion of livers was conducted to assess hepato-metabolic and cellular functions. The hepatic transport function, as indicated by canalicular excretion of indocyanine green, was improved in the HMP group than in the SCS group. The overall tissue viability, as indicated by oxygen consumption levels, was notably improved in HMP and control livers as compared to the SCS group. Higher bile production in both the preserved groups as compared to the fresh control livers could be a result of biliary edema and leakage of plasma into the canaliculus. The hepato-cellular injury, measured by ALT, release was significantly greater in the SCS group as compared to the HMP and control groups. These findings suggest that HMP could be a better method to preserve hepatic function and overall tissue viability as compared to SCS. Improved hepatic functions are indirect indicators of superior microcirculation and sinusoidal endothelial cell functions. Further studies in progress will evaluate these functions to confirm the significance of these observations.

Alanine Transaminase↗
PubMedDate not supplied

Suppression of cytokine-induced neutrophil accumulation in rat mesenteric venules in vivo by general anesthesia.

Most studies of neutrophil-endothelial interactions in vivo necessarily require the use of general anesthetic agents which are well known to be immunosuppressive. By using whole-mount preparations of the rat mesoappendix, we were able to study tumor necrosis factor alpha (TNF-alpha) induced neutrophil adhesion to the mesenteric venular endothelium in vivo without necessarily using general anesthesia. TNF-alpha significantly increased venular-neutrophil accumulation in a dose-dependent manner, accumulation was markedly increased at 1, 2, and 4 h, but returned to baseline after 24 h. After these preliminary dose-response and time-course studies, we evaluated the influence of standard clinically effective doses of several commonly used anesthetic agents (thiopental, pentobarbital, ketamine, alpha-chloralose, methoxyflurane, and halothane) on the extent of neutrophil-venular accumulation induced 2 h after intraperitoneal injection of 0.4 mg/kg TNF-alpha, compared to unanesthetized rats. All general anesthetics tested, with the exception of methoxyflurane, significantly suppressed this response. In most cases this suppression was striking (from 60 to 85%) such that a statistically significant proinflammatory response was obscured. Although methoxyflurane also tended to suppress this response to TNF-alpha, it was the only agent that allowed the response to be clearly seen. Because anesthesia markedly suppresses cytokine-induced neutrophil-venular adhesion, this model should provide an important complementary technique to the classical in vivo microcirculatory approaches which do necessarily require general anesthesia.

Anesthesia, General↗