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Biomedical subjects

M G Clemens

Publications and source records attributed to M G Clemens.

At least 73 records · Page 4Linked to original sources
PubMed1990

Calcium-free reperfusion prevents mitochondrial calcium accumulation but exacerbates injury.

Excessive accumulation of intracellular calcium has been proposed as a mediator of cell injury during ischemia and reperfusion. To test whether restriction of extracellular calcium might ameliorate hepatic injury following hypothermic ischemic preservation, isolated perfused rat livers were reperfused with a medium with normal extracellular calcium (mM-Ca) or no added calcium (microM-Ca) following 26 hr preservation at 4 degrees C. During reperfusion mitochondria from mM-Ca livers accumulated calcium and respiratory activity declined. Although mitochondrial calcium accumulation was prevented by microM-Ca reperfusion, damage to respiratory activity was exacerbated. Edema formation and loss of gluconeogenesis were similarly exacerbated in microM-Ca. This accelerated damage was not reversed by subsequent restoration of calcium. These results demonstrate that rather than ameliorating cell injury, calcium deprivation during reperfusion exacerbates damage to mitochondrial and cellular functions. Thus, cellular or mitochondrial calcium accumulation does not appear to be a sine qua non for hepatocyte injury during reperfusion following hypothermic ischemia.

Animals↗
PubMed1989

Adenosine triphosphate (ATP) treatment of hypoxic pulmonary hypertension (HPH): comparison of dose dependence in pulmonary and renal circulations.

In this study we investigated the relationship between pulmonary and renal responses to a low dose infusion of adenosine triphosphate-magnesium chloride (ATP-MgCl2) in a newborn piglet model of hypoxic pulmonary hypertension (HPH). Three- to five-day-old piglets were cannulated for the measurement of pulmonary and systemic arterial pressure, pulmonary and renal artery flow, and urine output. The animals were then made hypoxic by ventilation with a mixture containing 10% oxygen, 4% CO2, and balance nitrogen. Serial infusions of ATP-MgCl2 at 0.01, 0.025, 0.05, 0.1, 0.5, and 1.0 mg/kg/min were compared to preinfusion hypoxia baselines. Hypoxia alone produced a significant elevation in pulmonary artery pressure (73%) and a reduction in pO2. All dose rates of ATP-MgCl2 greater than or equal to 0.05 mg/kg/min produced a significant decrease in mean pulmonary artery pressure. However, as baseline mean pulmonary artery pressure increased there was an increased sensitivity to ATP-induced vasodilation. Pulmonary artery flow did not change during ATP infusion, thus, the change in pulmonary vascular resistance accounted for the decrease in pulmonary artery pressure. In contrast to the response of the pulmonary vasculature, systemic pressure was significantly decreased only during the 1.0 mg/kg/min infusion. Renal blood flow decreased by 46% during hypoxia and decreased further only during the highest dose rate of ATP infused (i.e., 1.0 mg/kg/min). Creatinine clearance (Ccr) and fractional reabsorption of Na (FreNa) also fell during hypoxia, but were not further altered during all but the highest dose of ATP infused.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMed1989

The effect of adenosine triphosphate on the functional status of the ductus arteriosus.

We investigated whether a low-dose infusion of ATP-MgCl2 could affect the functional status of the ductus arteriosus during hypoxia-induced pulmonary vasoconstriction. Three-day-old piglets were made hypoxic by ventilation with a mixture containing 10% oxygen, 4% CO2, and balance nitrogen. Serial infusions of ATP-MgCl2 at 0.1, 0.5, and 1.0 mg/kg/min were compared with preinfusion hypoxia baselines. The functional status of the ductus arteriosus was determined by change in transit time of a bolus of iced saline between thermistor probes in the pulmonary artery and aorta. The method was validated using a Blalock-Taussing shunt (subclavian to pulmonary artery) in 3-week-old piglets instrumented in a similar manner. In these three-day-old piglets, hypoxia alone produced a significant elevation in pulmonary artery pressure and reduction in PO2. All dose rates of ATP-MgCl2 produced a significant decrease in mean pulmonary artery pressure. Systemic pressure was significantly decreased only during the 1.0-mg/kg/min infusion. Transit times of a bolus of iced saline during the validation were definitive for characterizing a situation of "shunt open" or "shunt closed." Infusion of ATP-MgCl2 produced no change in the status of the ductus arteriosus in 45 (94%) of the determinations. In only three cases was the effect of ATP-MgCl2 sufficient to result in a functional change in the status of the ductus arteriosus. Pre- and postductal pulmonary artery PO2 were not altered during ATP-MgCl2 infusion, thus corroborating the transit time determinations. From these results, we conclude that an infusion of ATP-MgCl2 does not alter the functional status of the ductus arteriosus.

Adenosine Triphosphate↗
PubMed1988

Adenosine triphosphate: a potential therapy for hypoxic pulmonary hypertension.

In this study we investigated whether a low-dose infusion of ATP-MgCl2 could ameliorate the pulmonary hypertension resulting from hypoxic pulmonary vasoconstriction. Three-week-old piglets were anesthetized, intubated, ventilated with room air, and cannulated for the measurement of pulmonary and systemic arterial pressure and pulmonary artery flow (cardiac output). The ventilator inflow was then changed to a mixture containing 10% oxygen, 4% CO2, and balance nitrogen. Serial infusions of ATP-MgCl2 at 0.1, 0.5 and 1.0 mg/kg/min were compared to preinfusion hypoxia baselines. Hypoxia alone produced a significant elevation in pulmonary artery pressure. Although all dose rates of ATP-MgCl2 produced a significant decrease (30%) in mean pulmonary artery pressure, we observed a maximum decrease in MPAP at the lowest rate of ATP infusion. Pulmonary artery flow rose slightly during ATP infusion; therefore, it was the change in pulmonary vascular resistance that accounted for the decrease in pulmonary artery pressure. In contrast, the systemic pressure was significantly decreased only during the 1.0 mg/kg/min infusion. The predominant pulmonary effects are a result of the virtual clearance of ATP-MgCl2 in a single pass through the circulation. Adenosine in the presence or absence of MgCl2 produced only a 10% reduction in mean pulmonary artery pressure, and MgCl2 had no effect when infused alone. From these results, we conclude that a low-dose infusion of ATP-MgCl2 could ameliorate the vasoconstriction associated with hypoxic pulmonary hypertension without significant deleterious systemic side effects.

Adenosine Triphosphate↗
PubMed1988

Use of magnesium-ATP following liver ischemia.

The role of Mg in cardiomyopathies of different etiologies is well known; however, relatively little is known about the changes in hepatic Mg levels following ischemia to the liver. The available information indicates that tissue and mitochondrial Mg levels are altered following global hepatic ischemia and reflow and that such alterations may be responsible for the depressed cellular function during those conditions. Administration of MgCl2 alone following ischemia was ineffective in improving tissue and mitochondrial Mg levels and cellular functions. ATP administration alone following ischemia was also ineffective. However, administration of ATP complexed with MgCl2 increased tissue and mitochondrial Mg levels, tissue ATP stores and cellular functions and proved beneficial for the survival of animals. The potential mechanisms of the beneficial effects of ATP-MgCl2 are discussed. A multicenter clinical trial of ATP-MgCl2 in patients with various adverse circulatory conditions is being initiated in this country.

Adenosine Triphosphate↗
PubMed1988

Mechanism of calcium and magnesium translocation in acute pancreatitis: a temporal correlation between hypocalcemia and membrane-mediated excessive intracellular calcium accumulation in soft tissues.

Hypocalcemia frequently occurs in acute pancreatitis (AP), but its pathogenesis remains unknown. Since AP is often accompanied by acute alteration in the structure and function of cellular membranes, we investigated whether hypocalcemia associated with AP can be explained by acute translocation of Ca from extracellular to intracellular compartments. AP was induced in dogs by injection of autologous bile into the pancreatic duct, and in rats by controlled infusion of artificial bile containing Na-taurochlorate, Keflin, and trypsin into the cannulated bile duct. Plasma Ca, Mg, amylase, and PTH concentrations were determined in the serial samples. Tissue [Ca] and [Mg] were determined in pancreas, liver, kidney, and abdominal wall muscle biopsies obtained immediately before and 24 h after induction of AP in dogs or 2 h following induction of AP in rats to evaluate the temporal correlation between hypocalcemia and excessive intracellular Ca accumulation in soft tissues. Hypocalcemia (p less than 0.001) and hyperamylasemia (p less than 0.01) occurred within 6 h of AP in dogs, and persisted throughout. Plasma [Mg] was lowered and PTH activity was elevated at 6 and 18 h, and returned to a near normal level by 24 h. Concomitant with persisting hypocalcemia and lower ultrafilterable plasma [Ca2+], tissue [Ca] was significantly elevated in pancreas (71%), liver (24%), and abdominal muscle (112%), but was depleted in kidney by 25%. Pancreas biopsy following AP revealed histological signs of fulminant pancreatitis. [Mg] was depleted only in the pancreas (18%) and remained unaltered in other tissues. No significant changes were noted in the sham-operated animals. The observed temporal correlation between profound hypocalcemia and acute excessive intracellular Ca accumulation in soft tissues strongly suggests that hypocalcemia in AP may be precipitated by leaky-plasma-membrane-mediated excessive intracellular Ca accumulation. Similar data together with significantly reduced cellular energy charge (p less than 0.01) obtained from AP rats provided additional support to our hypothesis.

Acute Disease↗
PubMed1987

Alterations in hepatic membrane potentials in vivo during early and late sepsis.

To determine whether alterations in hepatocyte membrane electrical responses might play a role in glucose dyshomeostasis during sepsis, hepatocyte membrane potentials were measured in vivo in rats made septic by cecal ligation and puncture (CLP). In both early-septic (8-10 hr after CLP) and late-septic (18-20 hr after CLP) rats, resting hepatocyte membrane potentials were significantly depressed compared to those in sham-operated rats. In addition, the hyperpolarization response to glucagon administration in vivo which was observed in the sham-operated rats was significantly attenuated in both early- and late-sepsis rats. To determine whether this blunted hyperpolarization response was related to defects in stimulation of gluconeogenesis, livers from sham-operated and early-sepsis rats were isolated and perfused. The livers from sham-operated rats responded to 1 nM glucagon by increasing glucose release by 53%, while those from septic rats increased by only 20%. These results suggest that a defect associated with the plasma membrane may be an early event in the development of glucose dyshomeostasis during sepsis.

Animals↗
PubMed1986

Hepatic ischemia models for determining the effects of ATP-MgCl2 treatment.

Although ATP-MgCl2 treatment after global hepatic ischemia has been shown to improve cell function, a recent report has failed to confirm this in a model of regional hepatic ischemia. To determine the reason for this, rats were anesthetized and blood vessels to the left and median lobes of the liver were occluded. After 90 min of ischemia, the ligature around those vessels was removed. In Model 1, blood flow to the right lobes of the liver was then occluded whereas in Model 2, flow to those lobes was left intact. In both models the rats received intravenously 1.0 ml of saline or ATP-MgCl2 (12.5 mumole each) after ischemia. One hour after reflow, hepatic blood flow in the right and/or left lobe was measured following which mitochondria from the respective lobes were isolated and their function measured. The results indicated that although ATP-MgCl2 infusion following hepatic ischemia significantly improved hepatic blood flow and mitochondrial function in Model 1 (in which the right lobes were ligated following release of the occlusion to the left and median lobes), it failed to do so in Model 2 (in which the right lobes were not occluded after release of the occlusion to the left and median lobes). These results emphasize the importance of the rapid restoration of blood flow following hepatic ischemia. In the presence of shunts such as occur in Model 2, it is unlikely that any therapeutic agent would be effective.

Adenosine Triphosphate↗
PubMed1986

Reoxygenation injury in isolated hepatocytes: effect of extracellular ATP on cation homeostasis.

The aims of this study were to determine 1) the effects of anoxia and reoxygenation on electrolytes and ATP content of isolated hepatocytes and 2) whether exogenous ATP-MgCl2 has any beneficial effects on the cellular alterations that are produced during the reoxygenation period. After 90 min anoxia, intracellular Na and inorganic phosphate (Pi) increased, K and ATP decreased, whereas Ca and Mg did not change. After 60 min of reoxygenation, intracellular Mg and Na levels decreased, Ca increased, and Pi levels returned to normal, but ATP levels remained low. These results suggest that the plasma membrane is relatively impermeable to divalent ions such as Ca2+, Mg2+, and HPO2-4 during anoxia but becomes permeable to them after reoxygenation. When anoxic cells were treated with ATP-MgCl2 during reoxygenation, intracellular ATP and Mg levels increased, but accumulation of Ca and Pi was also observed. Thus enhancement of Mg transport and specific stimulation of Ca-Pi sequestration occurs with ATP-MgCl2 treatment. Na and K levels exhibited biphasic reciprocal dose-response changes to ATP-MgCl2 treatment; i.e., 0.1 mM ATP-MgCl2 (low-dose) treatment increased K and decreased Na, whereas 1 mM ATP-MgCl2 (high-dose) treatment decreased K and increased Na. These results indicate that although addition of a single high-dose ATP-MgCl2 was deleterious over a period of 60 min, low-dose ATP-MgCl2 accelerates the recovery of postanoxic cellular electrolyte homeostasis.

Adenosine Triphosphate↗
PubMed1986

The role of ATP-magnesium in ischemia and shock.

Although much is known about the role of Mg in cardiomyopathies of different etiology, very little is known about the changes in hepatic Mg levels following hemorrhagic shock or ischemia to the liver. Information available indicates that tissue and mitochondrial Mg levels may be altered following shock and ischemia and that such alterations may be responsible for the depressed cellular function during those conditions. MgCl2 administration following shock or ischemia was ineffective in improving tissue and mitochondrial Mg levels and cellular functions. Administration of ATP complexed with MgCl2, however, increased tissue and mitochondrial Mg levels, tissue ATP stores and cellular functions and proved beneficial for the survival of animals. ATP-MgCl2 administration also increased cardiac output while decreasing myocardial as well as total body O2 consumption. The potential mechanisms of the beneficial effects of ATP-MgCl2 are discussed. ATP-MgCl2 can be given safely to humans and it decreases myocardial O2 consumption and increases cardiac output without producing hypotension. A clinical trial of ATP-MgCl2 in patients with various adverse circulatory conditions is underway at our institution.

Adenosine Triphosphate↗
PubMed1985

Hepatic microcirculatory failure after ischemia and reperfusion: improvement with ATP-MgCl2 treatment.

Hepatic ischemia followed by reflow results in a myriad of metabolic and circulatory derangements that may eventually result in liver failure and death. In the present experiments we have used the technique of intravital fluorescence microscopy with fluoroscein isothiocyanate conjugated to bovine serum albumin as the intravascular fluorochrome to study the effects of ischemia and reperfusion on the hepatic microcirculation in vivo. Total hepatic ischemia was produced for 90 min to the left and median lobes of pentobarbital-anesthetized rats. After ischemia, reflow was allowed for 2 h. Three groups were studied: sham-ischemia controls and rats treated with either 1 ml saline or 12.5 mumol ATP-MgCl2 in 1-ml volume at the beginning of reflow. Although control rats exhibited stable microcirculation throughout the experiment, in saline-treated rats the number of perfused centrilobular areas and perfused sinusoids per unit area on the surface of the liver was decreased to approximately 50 and 40% of sham-ischemia controls, respectively. However, in rats treated with ATP-MgCl2 the density of perfused centrilobular areas and perfused sinusoids was 86 and 80% of sham-ischemia controls, respectively. From these results we conclude that intravital fluorescence microscopy is a potentially valuable method for the study of the hepatic microcirculation in vivo. Moreover, the results with ATP-MgCl2 treatment indicate that its effect on the microcirculation is a major factor in its beneficial effects on hepatic function after ischemia and reflow.

Adenosine Triphosphate↗
PubMed1985

Effects of regenerating liver cytosol on drug-induced hepatic failure.

Despite various interventions, the mortality rate after acute hepatic failure remains extremely high. Although it has been shown that administration of regenerating liver cytosol (RLC) after hepatic failure improves the survival rate of animals, the sequence in which various hepatic functions are altered after acute hepatic failure and their improvement by RLC remain unknown. To study this, fulminant hepatic failure in rats was produced by intraperitoneal injection of 1.5 gm/kg D-galactosamine (GAL). Twenty-four hours after 68% hepatectomy in normal rats, RLC was prepared and 4 ml of this solution (40 to 50 mg protein) was injected intraperitoneally in other animals at 6 or 24 hours after GAL administration. The long-term survival rate was 19.4% in the GAL-vehicle (control) group, 26.7% in the GAL-treated rats given liver cytosol from normal rats, and 72.2% (p less than 0.01 compared with both groups) in rats given RLC even 24 hours after GAL administration. Reticuloendothelial function was depressed at 24 and 48 hours after GAL administration; however, treatment with RLC but not vehicle or normal liver cytosol at 6 or even 24 hours after GAL administration significantly improved reticuloendothelial function 24 hours after GAL administration. DNA synthesis (an indicator of cell proliferation) did not increase in any group 24 hours after GAL administration; however, it increased strikingly at 48 hours in the GAL-RLC groups. Serum bilirubin levels were also lower in the RLC group 48 hours after GAL administration. Thus RLC administration improved survival, reticuloendothelial function, DNA synthesis, and hepatocyte function after GAL-induced acute hepatic failure. Improvement of reticuloendothelial function by RLC occurred before stimulation of DNA synthesis and appears to play an important role in improving survival after hepatic failure.

Animals↗
PubMed1984

Alterations in hepatic water and electrolyte balance in sepsis.

Since decreased nutrient flow has been proposed as the cause of hepatocellular dysfunction during sepsis, we studied hepatic Na+ and K+ balance in rats with sepsis to determine if these changes were consistent with ischemia-induced hepatocellular damage. Sepsis was produced in rats by cecal ligation and puncture (CLP). Seventeen to 19 hours following CLP, the rats were found to have late sepsis but not septic shock. At this time, either hepatic and RBC Na+ and K+ were determined in vivo, or the livers were isolated and perfused with Krebsbicarbonate buffer for 30 minutes prior to determining hepatic tissue Na+ and K+ levels. In contrast to previous reports of hemorrhagic shock and following hepatic ischemia, there was a significant increase in hepatic K+ in vivo and after 30 minutes of isolated perfusion in vitro. No significant changes were detected in RBC Na+ or K+. Thus, although decreased hepatic nutrient flow may develop during sepsis, hypoperfusion is not the cause of hepatocellular dysfunction.

Animals↗
PubMed1984

Hypothyroidism abolishes the hyperdynamic phase and increases susceptibility to sepsis.

To evaluate the role of thyroid hormones in sepsis, 250-400 g rats were surgically thyroidectomized and 2-6 weeks later sepsis was produced by cecal ligation and puncture (CLP). In normal rats, total body O2 consumption (VO2) increased by 12.8% (P less than 0.05) in early sepsis (6 hr after CLP) and decreased slightly in late sepsis (16 hr after CLP). In hypothyroid (HT) rats, VO2 was depressed by 19.8% (P less than 0.05) in early sepsis and further decreased to 46.7% (P less than 0.001) of preoperative levels in late sepsis. Hepatic blood flow increased in early sepsis in normal rats but was unchanged in HT rats. The normal hyperglycemic response to early sepsis was also absent in HT rats. The respiratory control ratio (RCR) of isolated mitochondria with succinate was not increased in HT rats in early sepsis. In late sepsis, hypothyroid animals showed further decreases in VO2 and mitochondrial RCR, and, in contrast to normal rats, showed no change in blood glucose levels. Survival (5 days) following late sepsis in normal, HT, and HT rats given daily ip injections of thyroxine (30 micrograms/kg) were 65.2% (15/23), 30% (6/20) (P less than 0.025), and 77.1% (14/18), respectively. Thus, absence of thyroid hormone abolishes the hyperdynamic phase of sepsis and significantly increases mortality in sepsis, and thyroxine replacement following thyroidectomy prevents the increased mortality from sepsis.

Animals↗
PubMed1984

ATP-MgCl2 produces sustained improvement in hepatic mitochondrial function and blood flow after hepatic ischemia.

Recent studies have shown that infusion of ATP-MgCl2 following hepatic ischemia significantly improved mitochondrial function and hepatic blood flow 1 hr after treatment. To determine if the improvement in the above parameters by ATP-MgCl2 is short-lived or whether it persists for prolonged periods of time after treatment, hepatic ischemia in rats was produced for 90 min followed by reperfusion. The rats then received iv 0.5 ml of saline or ATP-MgCl2 (12.5 mumole each). Twenty-four hours after reflow, hepatic blood flow was measured by H2 polarography following which the animals were sacrificed and hepatic mitochondria isolated. The results indicated that 24 hr after reflow, mitochondrial state 3 respiration, respiratory control ratio, adenine nucleotide translocase activity, ATP synthetic activity, and hepatic blood flow were depressed by approximately 50% in animals which were treated with saline after hepatic ischemia. In addition, there was a fourfold increase in mitochondrial free fatty acid levels of such animals. Animals which were treated with ATP-MgCl2 following hepatic ischemia showed significantly improved mitochondrial function (used as an index of cellular recovery) and hepatic blood flow. These results in conjunction with previous results suggest that infused ATP-MgCl2 improves mitochondrial function and blood flow and that these effects persist even 24 hr after administration of ATP-MgCl2. Thus, infusion of ATP-MgCl2 following severe ischemia produces sustained improvement in cellular function.

Adenosine Triphosphate↗