Search PubMed⌕ Search

Biomedical subjects

R L Barbour

Publications and source records attributed to R L Barbour.

35 records · Page 2Linked to original sources
PubMed1989

Intraperitoneal transplantation of microcarrier-attached enterocytes in rats.

The purpose of this study was to determine whether enterocyte transplantation could be used to correct a specific genetic metabolic defect. Bilirubin uridine diphosphoglucuronyl transferase (UDPGT) activity has been demonstrated in normal rat intestinal mucosa. We hypothesized that normal rat enterocyte transplantation may restore the ability of Gunn rats, which lack bilirubin UDPGT, to conjugate bilirubin. Small intestine was resected from normal Wistar rat donors. Enterocytes were harvested and suspended in Dulbecco's modified Eagle's medium with 10 percent fetal calf serum. Isolated enterocytes were attached to collagen-coated dextran microcarriers and transplanted into congeneic Gunn rat recipients. Recipient rats underwent bile duct cannulation after transplantation, and bile was analyzed for bilirubin glucuronides by high-pressure liquid chromatography. Fifty percent of the transplanted rats showed a significant increase in the concentration of bilirubin monoglucuronide and diglucuronide in their bile 4 and 7 days posttransplantation. Recipient rats had well vascularized microcarrier-enterocyte aggregates in the peritoneal cavity. Our method for intraperitoneal transplantation of isolated enterocytes in rats could potentially be used to correct specific enzymatic and metabolic defects.

Animals↗
PubMed1987

Effects of magnesium chloride on cardiovascular hemodynamics in the neurally intact dog.

To assess the cardiovascular actions of magnesium in neurally intact animals, magnesium chloride (1-4 mM/min) administered i.v., producing a peak arterial magnesium level between 4.7 and 7.2 mg/dl, was given to alpha-chloralose-anesthetized, open-chest dogs. Magnesium lowered heart rate by 36 +/- 11 beats/min (P less than .05), cardiac output by 0.7 +/- 0.2 liters/min (P less than .05), left ventricular (LV) peak dP/dt by 410 +/- 96 mm Hg/sec (P less than .05) and aortic and pulmonary artery pressures, but it did not change LV end-diastolic pressure, systemic resistance or pulmonary resistance. Coronary blood flow also decreased by 39 +/- 11% (P less than .05), myocardial oxygen consumption by 88 +/- 22% (P less than .05) and myocardial oxygen extraction by 53 +/- 16% (P less than .05). When heart rate was held constant, magnesium still decreased LV systolic pressure, LV peak dP/dt and coronary blood flow. The increase in serum magnesium was accompanied by an increase in serum calcium (by 1.4 +/- 0.2 mg/dl; P less than .05) and a fall in serum potassium (by 0.21 +/- 0.1 mEq/l), but not by a change in serum sodium, myocardial electrolyte arteriovenous differences or arterial pH. Thus, at blood concentrations that are observed in humans after therapeutic dosages of magnesium, a depression of cardiac performance is observed in the anesthetized dog. Although magnesium produces a fall in coronary blood flow, this appears to be due at least in part to a decrease in myocardial oxygen requirements because myocardial oxygen extraction also decreases. Rapid changes in serum electrolytes accompany these hemodynamic effects.

Animals↗
PubMed1984

Use of gated perfusion to study early effects of anoxia on cardiac energy metabolism: a new 31P NMR method.

A novel 31P NMR method is described that is capable of determining rapid changes in the intracellular levels of various phosphorus-containing compounds in an isolated, perfused working rat heart. This technique involves the gating of 31P NMR measurements to a heart that is alternately perfused with a modified Krebs-Henseleit medium containing 10 mM pyruvate and equilibrated with either 95% O2/5% CO2 or 95% N2/5% CO2. The experimental design allows up to three NMR measurements to be made during a single O2/N2 perfusion cycle. When these measurements are repeated at different intervals during the cycle, rapid changes in metabolite levels can be determined. Preliminary studies have shown that hearts remain hemodynamically stable to the aerobic/anoxic perfusion cycle as judged by heart rate, peak systolic pressure, aortic output, and coronary flow for at least 80 min in the magnet when subjected to cycle times of 4.5-s O2 and 1.5-s N2 perfusions. NMR measurements made under these conditions showed that a transition from full aerobic perfusion to this cycle revealed a new steady state, with an increased inorganic phosphate level from 6% total observable phosphorus to 10% and a possibly significant decreased measurement of creatine phosphate level (from 35 to 31%). Comparison of individual NMR measurements made during this perfusion cycle shows apparent rapid cyclical variations in intracellular pH and the levels of Pi, ATP, and NAD(H). These changes, expressed as variations above and below mean values measured during the cycle, showed that (a) intracellular pH, as measured by the chemical shift of Pi, reversibly decreases by more than 0.1 pH unit within 0.5-1 s following maximal anoxic perfusion and (b) coincident with a decrease in intracellular pH, Pi levels increased by a maximum of 30-40% whereas ATP levels decreased by a maximum of 15-20%. The amount of total observable phosphorous detected during the cycle is essentially constant. Unexpectedly, creatine phosphate levels are most stable, indicating that their levels are being maintained at the expense of ATP. Also unexpected is the finding that NAD(H) levels varied from maximal to undetectable levels during the perfusion cycle. The current method of aerobic/anoxic perfusion is capable of resolving metabolic events much faster than previous NMR methods and yielding information that is unobtainable by any other technique.

Adenosine Triphosphate↗
PubMed1984

Effect of creatine kinase activity on mitochondrial ADP/ATP transport. Evidence for a functional interaction.

Mitochondrial adenine nucleotide translocation was measured in the presence of creatine or creatine phosphate to test the proposed functional couple between the nucleotide translocase and creatine kinase. Rat heart mitochondria were preloaded with the corresponding nucleotide which reacts with creatine kinase only after it is transported across the mitochondrial membrane; namely, radioactive ATP-preloaded mitochondria were assayed in the presence of 10 mM creatine plus ADP, and radioactive ADP-preloaded mitochondria in the presence of 10 mM creatine phosphate plus ATP. Results showed that forward creatine kinase reaction (in the direction of creatine phosphate synthesis) inhibits translocation of external ADP into mitochondrial matrix and backward reaction (cleavage of creatine phosphate to creatine) likewise inhibits translocation of ATP across the mitochondrial membrane. Control experiments showed that without the kinase activity when Mg2+ was omitted from the assay medium, the presence of creatine or creatine phosphate had no effect on ADP or ATP transport, respectively. Therefore, the observed inhibition of nucleotide exchange by these compounds is due to creatine kinase activity which upon reacting with the newly exported nucleotide can effectively compete for transport back into the mitochondrial matrix over nucleotides added in the assay medium. Kinetic analysis also indicated that the forward creatine kinase reaction inhibits external ADP uptake competitively. These results are interpreted to support the proposal that a functional interaction exists between the mitochondrial bound creatine kinase and the adenine nucleotide translocase.

Adenosine Diphosphate↗
PubMed1983

Adenine nucleotide transport in hepatoma mitochondria. Characterization of factors influencing the kinetics of ADP and ATP uptake.

Initial velocity measurements of [3H]ADP and [3H]ATP uptake have been made with mitochondria isolated from Morris hepatomas of differing growth rates, and factors known to influence the rates of nucleotide exchange have been examined in an effort to determine whether the elevated rates of aerobic glycolysis in these tumors can be attributed to altered carrier activity. These studies included the determination of the apparent kinetic constants for nucleotide uptake as a function of the mitochondrial energy state and the dependence of transport rates on temperature. Also included in these studies were measurements of the mitochondrial levels of endogenous inhibitors, divalent cations and internal adenine nucleotides. Results obtained showed that with mitochondria isolated from the various tumor lines, the apparent kinetic constants for nucleotide uptake are different from those of control rat or regenerating liver mitochondria; the apparent Vmax values for both ADP and ADP uptake are significantly lower. Furthermore, under conditions of a high-energy state, the Km and Vmax values for ATP uptake are greater than the Km and Vmax value for ADP uptake but that under uncoupled conditions, the opposite is observed. Comparison of the levels of mitochondrial Ca2+, Mg2+, long-chain acyl-CoA ester and adenine nucleotide from the various mitochondria showed that important differences exist between liver and hepatoma mitochondria in the levels of Ca2+, long-chain acyl-CoA ester and AMP. Mitochondrial Ca2+ levels are elevated 3-5--fold in all tumor lines, and for Morris 7777 hepatoma (a rapidly growing tumor) by a remarkable 70-fold; whereas the levels of acyl-CoA ester and AMP are significantly lower in the more rapidly growing tumors. Arrhenius plots for nucleotide uptake in mitochondria from liver and hepatoma are characterized as being biphasic, having similar activation energies above and below the break point temperature (28-38 and 6-16 kcal/mol, respectively). However, the transition temperature for mitochondria from the various hepatomas is uniformly 4-5 degrees C lower than mitochondria from control liver. The latter difference may reflect a variation in membrane composition, most probably lipid components. It is concluded that the presence of elevated levels of Ca2+ and lower levels of AMP in hepatoma mitochondria and difference of membrane compositions may play an important role in limiting adenine nucleotide transport activity in vivo and that the impaired carrier activity may contribute to higher rates of aerobic glycolysis observed in these tumors.

Acyl Coenzyme A↗
PubMed1983

Adenine nucleotide transport in hepatoma mitochondria and its correlation with hepatoma growth rates and tumor size.

Initial rates of [3H]adenosine diphosphate and [3H]adenosine triphosphate uptake were measured in mitochondria isolated from normal rat liver, regenerating liver, mouse hepatoma BW7756, and four Morris hepatomas (7777, 7800, 7794A, and 16) of varying degrees of malignancy. Results obtained demonstrate that (a) the apparent Km and Vmax values for adenosine diphosphate and adenosine triphosphate uptake are significantly lower in hepatoma compared to normal or regenerating liver mitochondria, (b) the Vmax values for adenosine diphosphate uptake correlate with tumor growth rate, and (c) the Km values for adenosine triphosphate in both hepatoma and normal mitochondria are lowered in the presence of added uncoupling agents; however, the extent of decrease is much less in fast-growing tumors than in slow-growing tumors and normal tissues. Studies examining the causes of reduced transport rates in hepatoma mitochondria showed that they are independent of the mitochondrial energy state and associated with substantially lower levels of the total and exchangeable adenine nucleotides. Additional studies revealed that transport rates are also dependent on the size of the tumor from which the mitochondria are isolated. Mitochondria isolated from small tumors (less than 2 g) had higher transport rates as well as higher levels of exchangeable and total adenine nucleotides than those isolated from larger tumors (4 to 6 g). Endogenous inhibitor levels also varied as a function of tumor size; free fatty acid levels increased, whereas acyl coenzyme A levels declined in mitochondria isolated from larger tumors. These results seem to indicate that, during the progression of tumor growth, mitochondria are experiencing cellular environmental changes that will affect overall tumor cell metabolism.

Adenosine Diphosphate↗
PubMed1976

Purification and properties of ATPase inhibitor from rat liver mitochondria.

(1) The ATPase inhibitior protein has been isolated from rat liver mitochondria in purified form. The molecular weight determined by sodium dodecyl sulfate gel electrophoresis is approximately 9500, and the isoelectric point is 8.9. (2) The protein inhibits both the soluble ATPase and the particle-bound ATPase from rat liver mitochondria. It also inhibits ATPase activities of soluble F1, and inhibitor-depleted submitochondrial particles derived from bovine heart mitochondria. (3) On particle-bound ATPase the inhibitor has its maximal effect if incubated in the presence of Mg2+. ATP at slightly acidic pH. (4) The inhibitor has a minimal effect on Pi-ATP exchange activity in sonicated submitochondrial particles. However, unexpectedly the inhibitor greatly stimules Pi-ATP exchange activity in whole mitochondria while the low ATPase activity of the mitochondria is not affected. The possible mechanism of action of the inhibitor on intact mitochondria is offered.

Adenosine Triphosphatases↗
PubMedDate not supplied

Low extracellular magnesium results in cardiac failure in isolated perfused rat hearts.

Previous studies on isolated blood vessels indicate that acute withdrawal of extracellular magnesium ions ([Mg2+]o) induces calcium-dependent contractile responses, including coronary blood vessels. The present study, using isolated perfused rat hearts, was designed to assess whether low [Mg2+]o could result in cardiac failure and to gain some insight into the mechanism of action. The results show that both the myocardial oxygen consumption (by 29-38%) and oxygen tension in the coronary effluent decreased (by 18-26%) as the [Mg2+]o was decreased stepwise from 1.2 to 0.6, 0.3 and 0.0 mM. Linear-regression analysis of a plot of coronary flow versus the rate of oxygen consumption shows that there is a tendency for a rightward shift of this relationship in low [Mg2+]o and a leftward shift of the curve in elevated [Mg2+]o (4.8 mM). The experiments also show that with low [Mg2+]o, coronary flow declines 20-37%, and cardiac output and stroke volume fall 24-50% accompanied by 3- to 4-fold elevations in lactate production and eventual, irreversible cardiac failure. An interesting finding, of this study, is that the alpha-adrenoceptor constrictor agonist, phenylephrine (1-5 microM), was found to have effects very similar to low [Mg2+]o. This latter finding is consonant with our hypothesis that progressive lowering of extracellular, ionized magnesium initiates progressive coronary vasoconstriction, decreased tissue oxygenation and myocardial ischemia, which given time, in situ, in the intact host can lead to cardiac failure.

Animals↗
PubMedDate not supplied

Beneficial effects of high magnesium on alcohol-induced cardiac failure.

Although alcohol has long been known to induce cardiac depression and cardiomyopathy, it is not known whether drug therapy or pharmacologic manipulation can be used to prevent or reverse these toxicities. With this in mind, high levels (15 mM) of magnesium (Mg) were investigated for their potential antialcohol effects on perfused rat hearts. A high concentration of ethanol (135 mM) was used to induce rapid cardiac failure as assessed by hemodynamic and metabolic parameters. During ethanol perfusion in normal 1.2 mM [Mg2+]o physiologic salt solution, coronary flow decreased immediately, and all of the hemodynamic parameters studied (except for heart rate) were depressed significantly. After 10 min of 135 mM ethanol perfusion, only 60% of the hearts kept beating; at 15 min, only 42% of the hearts continued to beat. Myocardial metabolism under such conditions as assessed by examination of coronary effluent concentrations of lactic acid (LA), lactic acid dehydrogenase (LDH) and creatine phosphokinase (CPK) was rapidly and severely compromised. Although 15 mM MgSO4 alone did not alter coronary flow and systolic pressure under the conditions studied, it did decrease cardiac output, heart rate and total pressure developed. However, when 15 mM MgSO4 was given 10 min before ethanol, and continued during ethanol perfusion, the usual depression in all assessed cardiac hemodynamic parameters (except heart rate) caused by ethanol was not observed. During 15 min of high [Mg2+]o perfusion, coronary flow recovered from 19.1 +/- 6.8% (ethanol alone) to 68.1 +/- 9.9% of control values (p < 0.01); cardiac output recovered from 10.4 +/- 4.6% (ethanol alone) to 43.6 +/- 7.5% of control (p < 0.01); stroke volume went from 12.9 +/- 5.8% (ethanol alone) to 97.1 +/- 14.5% of control (p < 0.01); systolic pressure from 55.3 +/- 3.6% (ethanol alone) to 88.8 +/- 4.0% of control (p < 0.01), and total pressure developed from 23.9 +/- 7.8% (ethanol alone) to 35.0 +/- 4.5% of control (p < 0.05). Assessment of the metabolic biochemical parameters supported these changes in hemodynamic improvement. For example, LA, LDH and CPK all went from elevated values towards normal levels. There were similar hemodynamic and metabolic responses to high [Mg2+]o given during ethanol perfusion to that given before ethanol perfusion. The hemodynamic and metabolic beneficial effects between groups pretreated or treated with high [Mg2+]o exhibited no significant differences. These results suggest that high [Mg2+]o (15 mM) given either before or during ethanol-induced cardiotoxicity is effective in attenuating both functional and metabolic damage caused by high ethanol perfusion in the rat heart.

Animals↗
PubMedDate not supplied

Influence of Mg2+ on cardiac performance, intracellular free Mg2+ and pH in perfused hearts as assessed with 31P nuclear magnetic resonance spectroscopy.

The cellular bioenergetic responses of isolated perfused working rat hearts to alterations in hemodynamic function caused by acute exposure to elevated levels of extracellular magnesium ions ([Mg2+]o) were examined using 31P nuclear magnetic resonance (31P NMR) spectroscopy. Results showed that in hearts working against 90 cm H2O afterload, an increase in [Mg2+]o from 1.2 to 4.8 mM reduced the heart rate by 35%, while coronary flow was increased by 38%. Unexpectedly, despite the pronounced bradycardia, the rate-pressure product was reduced only slightly (from 2.36 x 10(4) to 2.08 x 10(4) mm Hg/min) due to a significant increase (36%) in systolic pressure. In addition, cardiac output actually increased by 23%, owing to a > 100% increase in stroke volume, indicating that the performance of the heart was improved and suggesting that the efficiency of the heart was improved as well. In a separate series of experiments, 31P NMR measurements performed on hearts perfused in the Langendorff mode revealed that elevated levels of [Mg2+]o increase phosphocreatine (PCr) levels by 23% (from 9.2 to 11.3 mM), while Pi levels declined by a corresponding amount. Perfusion of hearts in the working mode with elevated [Mg2+]o was also observed to increase PCr levels from 6.3 to 9.0 mM, while ATP levels declined by 17%. Measurement of the chemical shift difference between Pi and PCr and that between the alpha and beta phosphate resonances of ATP were used to determine intracellular pH and the cytosolic levels of free Mg2+ ([Mg2+]i), respectively. These results showed that acute exposure of hearts, perfused in either the working or Langendorff mode, to increased levels of [Mg2+]o increased intracellular pH by 0.12-0.13 units, while free Mg2+ nearly doubled to a level of 1.1-1.2 mM. The latter observation may suggest that acute variations in the level of [Mg2+]o can influence a multitude of cellular processes requiring Mg2+ as an essential cofactor. Using the above data and assuming equilibrium of the creatine kinase reaction, the levels of ADP, cytosolic phosphorylation potential ([ATP]/[ADP][Pi]) and free energy change from ATP hydrolysis (-delta G/delta E) were also calculated. Results obtained illustrate that in the presence of elevated [Mg2+]o, ADP levels declined by 33-48%, the cytosolic phosphorylation potential increased from 41 to 112 mM-1 and -delta G/delta E increased from 56.7 to 59.3 kJ/mol. These changes are not completely accountable by the known bradycardia and vasodilatory effects of elevated [Mg2+]o and strongly argue for a direct action of [Mg2+]o on the myocyte as well.(ABSTRACT TRUNCATED AT 400 WORDS)

Adenosine Triphosphate↗