Enhanced glucose uptake via GLUT4 fuels recovery from calcium overload after ischaemia-reperfusion injury in sevoflurane- but not propofol-treated hearts

BACKGROUND

So far, no study has explored the effects of sevoflurane, propofol, and Intralipid on metabolic flux rates of fatty acid oxidation (FOX) and glucose oxidation (GOX) in hearts exposed to ischaemia-reperfusion.

METHODS

Isolated paced working rat hearts were exposed to 20 min of ischaemia and 30 min of reperfusion. Peri-ischaemic sevoflurane (2 vol%) and propofol (100 µM) in the formulation of 1% Diprivan(®) were assessed for their effects on oxidative energy metabolism and intracellular diastolic and systolic Ca(2+) concentrations. Substrate flux was measured using [(3)H]palmitate and [(14)C]glucose and [Ca(2+)] using indo-1AM. Western blotting was used to determine the expression of the sarcolemmal glucose transporter GLUT4 in lipid rafts. Biochemical analyses of nucleotides, ceramides, and 32 acylcarnitines were also performed.

RESULTS

Sevoflurane, but not propofol, improved the recovery of left ventricular work (P=0.008) and myocardial efficiency (P=0.008) compared with untreated ischaemic hearts. This functional improvement was accompanied by reduced increases in post-ischaemic diastolic and systolic intracellular Ca(2+) concentrations (P=0.008). Sevoflurane, but not propofol, increased GOX (P=0.009) and decreased FOX (P=0.019) in hearts exposed to ischaemia-reperfusion. GLUT4 expression was markedly increased in lipid rafts of sevoflurane-treated hearts (P=0.016). Increased GOX closely correlated with reduced Ca(2+) overload. Intralipid alone decreased energy charge and increased long-chain and hydroxyacylcarnitine tissue levels, whereas sevoflurane decreased toxic ceramide formation.

CONCLUSIONS

Enhanced glucose uptake via GLUT4 fuels recovery from Ca(2+) overload after ischaemia-reperfusion in sevoflurane- but not propofol-treated hearts. The use of a high propofol concentration (100 µM) did not result in similar protection.

Comparison of four strategies to reduce the pain associated with intravenous administration of rocuronium

BACKGROUND

I.V. rocuronium produces intense discomfort at the site of injection in conscious patients. Four strategies to reduce or prevent this discomfort were studied.

METHODS

Two hundred and fifty adult patients, ASA I-III, were randomized into five groups of 50 patients in a blinded, prospective study. The control group received rocuronium 10 mg alone. For the remaining four groups, rocuronium 10 mg was mixed with sodium bicarbonate 8.4% 2 ml, fentanyl 100 micro g, lidocaine 2% or normal saline. The pH and osmolality of all mixtures were measured. Patient data were analysed using ordinal logistic regression. Osmolality and pH data were analysed using the Kruskal-Wallis test with Dunn's multiple comparison test.

RESULTS

When compared with rocuronium alone, only the addition of saline failed to significantly reduce the pain reported by patients. The addition of fentanyl reduced the complaint of pain by 1.9 times (P<0.049) and the addition of lidocaine 2% reduced it by 3.6 times (P<0.0001). Sodium bicarbonate 8.4% reduced the reporting of pain by 18.4 times (P<0.0001).

CONCLUSIONS

Sodium bicarbonate 8.4%, when added to rocuronium, markedly reduces the experience of pain during the i.v. administration of a small dose of rocuronium.

Angiotensin II reduces infarct size and has no effect on post-ischaemic contractile dysfunction in isolated rat hearts

1. In order to test the hypothesis that angiotensin II exacerbates myocardial ischaemia-reperfusion (IR) injury, we examined the effects of graded angiotension II concentrations of angiotensin II on IR injury in both working and non-working (Langendorff) isolated rat hearts. 2. Non-working hearts were subjected to 30 min aerobic perfusion (baseline) then 25 min of global, no-flow ischaemia followed by 30 min of reperfusion either in the absence (control, n=7) or presence of 1 (n=6) or 10 nM (n=5) angiotensin II). Recoveries of LV developed pressure and coronary flow after 30 min reperfusion in control hearts (58+/-9 and 40+/-8% of baseline levels, respectively) were no different from hearts treated with 1 or 10 nM angiotensin II. Infarct size (determined at the end of reperfusion by triphenyltetrazolium chloride staining) was reduced by angiotensin II in a concentration-dependent manner (from a control value of 27+/-3 to 18+/-4% and 9+/-3% of the LV, respectively). 3. Working hearts were subjected to 50 min pre-ischaemic (pre-I) aerobic perfusion then 30 min of global, no-flow ischaemia followed by 30 min of reperfusion either in the absence (control, n=14) or presence of 1 (n=8), 10 (n=7) or 100 nM (n=7) angiotensin II). In controls, post-ischaemic (post-I) left ventricular (LV) work and efficiency of oxygen consumption were depressed (43+/-9 and 42+/-10% of pre-I levels, respectively). The presence of angiotensin II throughout IR had no effect on LV work compared with control. 4. Thus, angiotensin II reduces infarct size in a concentration-dependent manner but has no effect on contractile stunning associated with IR in isolated rat hearts.

Dichloroacetate improves cardiac efficiency after ischemia independent of changes in mitochondrial proton leak

Dichloroacetate (DCA) is a pyruvate dehydrogenase activator that increases cardiac efficiency during reperfusion of ischemic hearts. We determined whether DCA increases efficiency of mitochondrial ATP production by measuring proton leak in mitochondria from isolated working rat hearts subjected to 30 min of ischemia and 60 min of reperfusion. In untreated hearts, cardiac work and efficiency decreased during reperfusion to 26% and 40% of preischemic values, respectively. Membrane potential was significantly lower in mitochondria from reperfused (175.6 +/- 2.2 mV) versus aerobic (185.8 +/- 3.1 mV) hearts. DCA (1 mM added at reperfusion) improved recovery of cardiac work (1.9-fold) and efficiency (1.5-fold) but had no effect on mitochondrial membrane potential (170.6 +/- 2.9 mV). At the maximal attainable membrane potential, O(2) consumption (nmol O(2) x mg(-1) x min(-1)) did not differ between untreated or DCA-treated hearts (128.3 +/- 7.5 and 120.6 +/- 7.6, respectively) but was significantly greater than aerobic hearts (76.6 +/- 7.6). During reperfusion, DCA increased glucose oxidation 2.5-fold and decreased H(+) production from glucose metabolism to 53% of untreated hearts. Because H(+) production decreases cardiac efficiency, we suggest that DCA increases cardiac efficiency during reperfusion of ischemic hearts by increasing the efficiency of ATP use and not by increasing the efficiency of ATP production.

Enhanced expression of angiotensin II type 2 receptor, inositol 1,4, 5-trisphosphate receptor, and protein kinase cepsilon during cardioprotection induced by angiotensin II type 2 receptor blockade

We hypothesized that the cardioprotective effect of angiotensin II type 2 receptor (AT(2)R) blockade with PD 123,319 (PD) on the recovery of left ventricular (LV) mechanical function after ischemia/reperfusion (IR) in the isolated working rat heart is associated with the enhanced expression of AT(2)R protein and mRNA as well as an increase in inositol 1,4,5-trisphosphate type 2 receptor (IP(3)R) and protein kinase Cepsilon (PKCepsilon) proteins. We assessed AT(2)R, angiotensin II type 1 receptor (AT(1)R), IP(3)R, and PKCepsilon protein expression (Western blots) and AT(2)R mRNA levels (Northern blots) in myocardium from isolated working rat hearts that were subjected to global ischemia (30 minutes) followed by reperfusion (30 minutes). Groups of adult rat hearts (n=6) were exposed to no IR, no IR+PD (0.3 micromol/L), IR, and IR+PD. Compared with no IR and no IR+PD, IR decreased (P<0.05) functional recovery and AT(2)R mRNA and protein, as well as AT(1)R mRNA (not protein) and IP(3)R and PKCepsilon proteins. Compared with IR, PD+IR improved LV functional recovery (P<0.05) and markedly increased AT(2)R mRNA and protein (P<0.001). However, PD did not change AT(1)R mRNA or protein. More importantly, PD+IR markedly increased IP(3)R and PKCepsilon proteins. The downregulation of AT(2)R mRNA and protein with IR and their upregulation with PD indicate that the effects of PD are AT(2)R specific. The overall results suggest that the cardioprotective effect of acute PD treatment on LV functional recovery after IR in the isolated working rat heart is specifically due to AT(2)R blockade and is associated with enhanced downstream IP(3)R and PKCepsilon signaling.

Characterization of cardioprotection mediated by AT2 receptor antagonism after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

Whether cardioprotection induced by the angiotensin II (AngII) type 2 receptor (AT(2)R) antagonist PD123,319 (PD) after ischemia-reperfusion (IR) is influenced by the concentration of PD, presence of AngII, timing of exposure, or inhibition of proton production from glucose metabolism is not known.

METHODS AND RESULTS

We examined these factors in isolated working rat hearts subjected to IR injury, no treatment (control), or treatment with N(6)-cyclohexyl adenosine (CHA, 0.5 micromol/L), an adenosine A(1) receptor agonist that induces cardioprotection by decreasing protons ("positive" control). Compared with control, 1 micromol/L PD present throughout IR improved recovery of left ventricular work (73 +/- 5 vs. 40 +/- 8%) to the level with CHA (82 +/- 5%), but 0.1 micromol/L PD did not (58 +/- 6 vs. 40 +/- 8%). AngII (1 nmol/L) did not effect postischemic recovery associated with 1 micromol/L PD (73 +/- 7%) but improved that associated with 0.1 micromol/L PD (86 +/- 3%). PD (1 micromol/L), present solely during reperfusion, enhanced postischemic left ventricular recovery to 72 +/- 5%. Also, PD (1 micromol/L) did not affect glycolytic rates or proton production in nonischemic or IR hearts.

CONCLUSION

PD-induced cardioprotection is 1) PD concentration-dependent, 2) AngII-sensitive, 3) mediated during reperfusion, and 4) independent of proton production, suggesting that reduction in IR injury and indirect AT(1)R stimulation might be involved.

Phentolamine prevents the adverse effects of adenosine on glycolysis and mechanical function in isolated working rat hearts subjected to antecedent ischemia

Adenosine inhibits glycolysis from exogenous glucose, reduces proton production and enhances post-ischemic left ventricular minute work (LV work) following ischemia in isolated working rat hearts perfused with glucose and fatty acids. In hearts partially depleted of glycogen by antecedent ischemic stress (AIS)--two cycles of ischemia (10 min) and reperfusion (5 min)--adenosine stimulates rather than inhibits glycolysis, increases proton production and worsens recovery of post-ischemic LV work. We determined if the switch in adenosine effect on glycolysis and recovery of LV work following ischemia in hearts subject to AIS was due to the reduction in glycogen content per se or because of alpha-adrenoceptor stimulation. One series of hearts underwent a 35-min period of substrate-free Langendorff perfusion (substrate-free glycogen depletion; SFGD) and a second series of hearts was subjected to AIS. Both series of hearts had a similar glycogen content (approximately 70 micromol/g dry wt) prior to drug treatment. In SFGD hearts perfused aerobically, adenosine (500 microM) inhibited glycolysis from exogenous glucose and reduced proton production. In SFGD hearts reperfused after prolonged ischemia, adenosine exerted similar effects on glucose metabolism and enhanced recovery of post-ischemic LV work (87.2 +/- 2.2% of preischemic values) relative to untreated hearts (25.9 +/- 13.3% of preischemic values). In AIS hearts perfused aerobically or subject to ischemia and reperfusion, phentolamine (1 microM) given in combination with adenosine, prevented adenosine-induced stimulation of glycolysis from exogenous glucose and reduced calculated proton production from glucose. Recoveries of post-ischemic LV work in AIS hearts for untreated, adenosine, phentolamine and adenosine/phentolamine groups were 34.4 +/- 11.4%, 8.6 +/- 3.9%, 16.3 +/- 13.5% and 73.2 +/- 13.1% respectively, of preischemic values. Glycogen depletion in the absence of ischemia does not switch the effect of adenosine from inhibition to stimulation of glycolysis or alter the cardioprotective properties of adenosine in hearts subject to ischemia and reperfusion. The detrimental switch in the metabolic and cardioprotective effects of adenosine, in hearts subject to AIS, can be prevented by phentolamine, an alpha-adrenoceptor antagonist. These data support the concept that modulation of glucose metabolism is an important factor in the mechanical functional recovery of the post-ischemic heart.

Activation of Ca(2+)-independent nitric oxide synthase by 17beta-estradiol in post-ischemic rat heart

BACKGROUND

Nitric oxide (NO) donors or facilitation of endogenous NO production is cardioprotective. This study sought to determine whether enhanced myocardial NO production might contribute to estrogen-induced cardioprotection.

METHODS

Ca(2+)-dependent and Ca(2+)-independent NOS activities (pmol min(-1) mg(-1) protein), NOS protein expression (quantitative immunoblot), cGMP content (pmol mg(-1) protein) and LV work (Joules) were measured in hearts isolated from ovariectomized rats that were either untreated or treated chronically with 17beta-estradiol (0.25 mg, 21 day release formulation).

RESULTS

After 14 days, serum levels of 17beta-estradiol were 6+/-1 and 135+/-16 pg ml(-1) in untreated and 17beta-estradiol-treated animals, respectively. After 60 min aerobic working mode perfusion, Ca(2+)-dependent NOS (untreated, 1.47+/-0.36; 17beta-estradiol 1.13+/-0.25) and Ca(2+)-independent NOS (untreated, 0.45+/-0.24; 17beta-estradiol, 0.41+/-0.21) activities, eNOS and iNOS proteins and cGMP content (untreated, 0.64+/-0.08; 17beta-estradiol, 0.76+/-0.12) were not different in the two groups. After 60 min low-flow (0.5 ml min(-1)) ischemia and 30 min reperfusion, Ca(2+)-dependent NOS activities were again similar (untreated, 1.25+/-0.23; 17beta-estradiol, 0.78+/-0.27). However, after reperfusion, Ca(2+)-independent NOS activity (untreated, 0. 39+/-0.10; 17beta-estradiol, 1.36+/-0.36) was 3.5-fold higher (P=0. 008) and cGMP content (untreated, 0.30+/-0.03; 17beta-estradiol, 0. 49+/-0.07) was 1.6-fold higher (P=0.017) in hearts from 17beta-estradiol-treated animals. Although pre-ischemic function was similar, recovery of post-ischemic LV work was 2-fold greater (P=0.024) in the 17beta-estradiol group.

CONCLUSION

The ability of ischemia and reperfusion in combination with chronic 17beta-estradiol to increase Ca(2+)-independent NOS activity and cGMP content supports a role for enhanced myocardial NO signaling in 17beta-estradiol-induced cardioprotection.

Enhancement of post-ischemic myocardial function by chronic 17 beta -estradiol treatment: role of alterations in glucose metabolism

This study was designed to assess the effects of chronic estrogen replacement therapy on mechanical function and glucose utilization in aerobic and post-ischemic hearts. Ovariectomized female rats were either untreated or were treated subcutaneously with 17 beta -estradiol (0.25 mg 21-day slow release pellets). After 14 days, when serum concentrations of 17 beta -estradiol were 3.8+/-0.8 and 148+/-15 pg/ml, respectively, hearts were isolated and perfused in working mode with Krebs-Henseleit solution containing 1.2 m m palmitate and 11 m m[5-(3)H/U-(14)C]glucose. Hearts were perfused aerobically (60 min) and then subjected to low-flow ischemia (0.5 ml/min, 60 min) followed by reperfusion (30 min). During reperfusion, hearts from rats treated chronically with 17 beta -estradiol had an improved (two-fold) recovery of mechanical function. 17 beta -estradiol (400 p m, 109 pg/ml), when present acutely in heart perfusate during ischemia and reperfusion, did not improve recovery. Chronic 17 beta -estradiol increased glucose oxidation during reperfusion as well as during aerobic perfusion but had no effect on glycolysis. Chronic 17 beta -estradiol also altered post-ischemic glycogen metabolism and increased glycogen content and glycogen synthase activity at the end of reperfusion. As stimulation of glucose oxidation has been shown previously to be cardioprotective, and as the enhanced rate of glucose oxidation was not simply a consequence of enhanced recovery of mechanical function, alterations in glycogen and glucose utilization may contribute to the direct cardioprotective effects of chronic estrogen treatment.

Estimation of desflurane concentration using isoflurane channel in optical infrared analyzer

PURPOSE

To estimate desflurane concentration on the isoflurane channel in an optical infrared analyzer using a simple regression equation.

METHODS

Desflurane in concentrations of 0% to 3% in 0.5% increments and 3% to 12% in 1% increments in 2 L.min-1 oxygen was delivered simultaneously to an Ohmeda 5250 RGM desflurane channel, an Ohmeda 5250 RGM isoflurane channel, and a Datex Capnomac Ultima isoflurane channel at room temperature and atmospheric pressure. For each concentration increment, the displayed gas concentrations were recorded. By comparing the readings from the desflurane channel of Ohmeda RGM and the isoflurane channels from Ohmeda RGM and Datex Capnomac Ultima respectively, the linear regression relationship and the slope of the fitted line (conversion factor) between two channels were obtained. Similar measurements were performed using 2 L.min-1 mixture of nitrous oxide 50% and oxygen 50%. The measurements were repeated with different monitors three months later.

RESULTS

All four analysers tested were linear (r2 > 0.9) for measuring desflurane using isoflurane channels over the range of concentrations studied on two different days. The accuracy of the estimation using the mean conversion factor of the four monitors was within 10% error from the readings of the commercially available desflurane channel analyzer. There was no noticeable effect on the slope (conversion factor) of the linear regression with O2 100% or 50/50 mixture of N2O and O2.

CONCLUSION

The concentration of desflurane can be estimated by a simple conversion factor using an isoflurane channel of an infrared system.

The growth of microorganisms in propofol and mixtures of propofol and lidocaine

Propofol emulsion supports bacterial growth. Extrinsic contamination of propofol has been implicated as an etiological event in postsurgical infections. When added to propofol, local anesthetics (e.g., lidocaine) alleviate the pain associated with injecting it. Because local anesthetics have antimicrobial activity, we determined whether lidocaine would inhibit microbial growth by comparing the growth of four microorganisms in propofol and in mixtures of propofol and lidocaine. Known quanta of Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Candida albicans were inoculated into solutions of 1% propofol, 0.2% lidocaine in propofol, 0.5% lidocaine in propofol, 0.5% lidocaine in isotonic sodium chloride solution, and 0.9% isotonic sodium chloride solution. All microorganisms were taken from stock cultures and incubated for 24 h. Growth of microorganisms in each solution was compared by counting the number of colony-forming units grown from a subculture of the solution at 0, 3, 6, 12 and 24 h. Propofol supported the growth of E. coli and C. albicans. Propofol maintained static levels of S. aureus and was bactericidal toward P. aeruginosa. The addition of 0.2% and 0.5% lidocaine to propofol failed to prevent the growth of the studied microorganisms. The effect of 0.5% lidocaine in isotonic sodium chloride solution did not differ from the effects of isotonic sodium chloride solution alone. We conclude that lidocaine, when added to propofol in clinically acceptable concentrations, does not exhibit antimicrobial properties.

IMPLICATIONS

Local anesthetics such as lidocaine have antimicrobial activity. Propofol supports the growth of bacteria responsible for infection. Bacteria were added to propofol and propofol mixed with lidocaine. The addition of lidocaine to propofol in clinically relevant concentrations did not prevent the growth of bacteria. The addition of lidocaine to propofol cannot prevent infection from contaminated propofol.

Assessment of glycogen turnover in aerobic, ischemic, and reperfused working rat hearts

Glycogen and its turnover are important components of myocardial glucose metabolism that significantly impact on postischemic recovery. We developed a method to measure glycogen turnover (rates of glycogen synthesis and degradation) in isolated working rat hearts using [3H]- and [14C]glucose. In aerobic hearts perfused with 11 mM glucose, 1.2 mM palmitate, and 100 microU/ml insulin, rates of glycogen synthesis and degradation were 1.24 +/- 0.3 and 0.53 +/- 0. 25 micromol. min-1. g dry wt-1, respectively. Low-flow ischemia (0.5 ml/min, 60 min) elicited a marked glycogenolysis; rates of glycogen synthesis and degradation were 0.54 +/- 0.16 and 2.12 +/- 0.14 micromol. min-1. g dry wt-1, respectively. During reperfusion (30 min), mechanical function recovered to 20% of preischemic values. Rates of synthesis and degradation were 1.66 +/- 0.16 and 1.55 +/- 0. 21 micromol. min-1. g dry wt-1, respectively, and glycogen content remained unchanged (25 +/- 3 micromol/g dry wt). The assessment of glycogen metabolism needs to take into account the simultaneous synthesis and degradation of glycogen. With this approach, a substantial turnover of glycogen was detectable not only during aerobic conditions but also during ischemia as well as reperfusion.

Acute effects of triiodothyronine on glucose and fatty acid metabolism during reperfusion of ischemic rat hearts

Clinical studies have demonstrated improved myocardial recovery after severe ischemia in response to acute triiodothyronine (T3) treatment. We determined whether T3 improves the recovery of ischemic hearts by improving energy substrate metabolism. Isolated working rat hearts were perfused with 5.5 mM glucose and 1.2 mM palmitate and were subjected to 30 min of no-flow ischemia. Glycolysis, glucose oxidation, and palmitate oxidation were measured during aerobic reperfusion by adding [5-3H]glucose, [U-14C]glucose, or [9,10-3H]palmitate to the perfusate, respectively. During reperfusion, cardiac work in untreated hearts recovered to a lesser extent than myocardial O2 consumption (MVO2), resulting in a decreased recovery of cardiac efficiency, which recovered to only 25% of preischemic values. Treatment of hearts with T3 (10 nM) before ischemia increased glucose oxidation during reperfusion, which was associated with a significant increase in pyruvate dehydrogenase (PDH) activity, the rate-limiting enzyme for glucose oxidation. In contrast, T3 had no effect on MVO2, glycolysis, or palmitate oxidation. This resulted in a significant decrease in H+ production from glycolysis uncoupled from glucose oxidation (2.7 +/- 0.3 and 1.9 +/- 0.3 micromol . g dry wt-1 . min-1 in control and T3-treated hearts, respectively, P < 0.05), as well as a 3.2-fold improvement in cardiac work and a 2.3-fold increase in cardiac efficiency compared with untreated postischemic hearts (P < 0.05). These data suggest that T3 can exert acute effects that improve the coupling of glycolysis to glucose oxidation, thereby decreasing H+ production and increasing cardiac efficiency as well as contractile function during reperfusion of the postischemic heart.

K(ATP)-channel activation: effects on myocardial recovery from ischaemia and role in the cardioprotective response to adenosine A1-receptor stimulation

1. Optimization of myocardial energy substrate metabolism improves the recovery of mechanical function of the post-ischaemic heart. This study investigated the role of K(ATP)-channels in the regulation of the metabolic and mechanical function of the aerobic and post-ischaemic heart by measuring the effects of the selective K(ATP)-channel activator, cromakalim, and the effects of the K(ATP)-channel antagonist, glibenclamide, in rat fatty acid perfused, working hearts in vitro. The role of K(ATP) channels in the cardioprotective actions of the adenosine A1-receptor agonist, N6-cyclohexyladenosine (CHA) was also investigated. 2. Myocardial glucose metabolism, mechanical function and efficiency were measured simultaneously in hearts perfused with modified Krebs-Henseleit solution containing 2.5 mM Ca2+, 11 mM glucose, 1.2 mM palmitate and 100 mu l(-1) insulin, and paced at 300 beats min(-1). Rates of glycolysis and glucose oxidation were measured from the quantitative production of 3H20 and 14CO2, respectively, from [5-3H/ U-14C]-glucose. 3. In hearts perfused under aerobic conditions, cromakalim (10 microM), CHA (0.5 microM) or glibenclamide (30 microM) had no effect on mechanical function. Cromakalim did not affect glycolysis or glucose oxidation, whereas glibenclamide significantly increased rates of glycolysis and proton production. CHA significantly reduced rates of glycolysis and proton production but had no effect on glucose oxidation. Glibenclamide did not alter CHA-induced inhibition of glycolysis and proton production. 4. In hearts reperfused for 30 min following 30 min of ischaemia, left ventricular minute work (LV work) recovered to 24% of aerobic baseline values. Cromakalim (10 microM), administered 5 min before ischaemia, had no significant effect on mechanical recovery or glucose metabolism. CHA (0.5 microM) significantly increased the recovery of LV work to 67% of aerobic baseline values and also significantly inhibited rates of glycolysis and proton production. Glibenclamide (30 microM) significantly depressed the recovery of mechanical function to < 1% of aerobic baseline values and stimulated glycolysis and proton production. 5. Despite the deleterious actions of glibenclamide per se in post-ischaemic hearts, the beneficial effects of CHA (0.5 microM) on the recovery of mechanical function and proton production were not affected by glibenclamide. 6. The data indicate that the cardioprotective mechanism of adenosine A1-receptor stimulation does not involve the activation of K(ATP)-channels. Furthermore, in rat fatty acid perfused, working hearts, stimulation of K(ATP)-channels is not cardioprotective and has no significant effects on myocardial glucose metabolism.

Cardioprotection by activation of NO/cGMP pathway after cardioplegic arrest and 8-hour storage

BACKGROUND

We determined whether activation of the nitric oxide/cyclic guanosine monophosphate pathway by sodium nitroprusside (SNP) protects hearts subjected to cardioplegic arrest and prolonged hypothermic storage.

METHODS

Isolated rat hearts arrested with St. Thomas' II cardioplegia and stored at 3 degrees +/- 1 degree C for 8 hours were reperfused at 37 degrees C in Langendorff (10 minutes) and working (60 minutes) modes.

RESULTS

During reperfusion, left ventricular work was depressed in stored hearts relative to fresh hearts. When present during arrest, storage, and both reperfusion phases, SNP (200 mumol/L) improved work to values close to those in fresh hearts. When added only during the 10-minute period of Langendorff reperfusion, SNP also improved the subsequent recovery of work. This effect was antagonized by the soluble guanylyl cyclase inhibitor 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ). Poststorage coronary perfusion was not increased by SNP.

CONCLUSIONS

The ability of SNP to enhance recovery independent of changes in coronary perfusion and in an ODQ-sensitive manner suggests that SNP-induced protection is due to activation of the myocardial nitric oxide/cyclic guanisine monophosphate pathway. These results suggest that supplementing cardioplegic solutions with SNP, administering SNP during early reperfusion, or both may offer additional means to improve donor heart preservation.

Intrinsic ANG II type 1 receptor stimulation contributes to recovery of postischemic mechanical function

To determine whether intrinsic angiotensin II (ANG II) type 1 receptor (AT1-R) stimulation modulates recovery of postischemic mechanical function, we studied the effects of selective AT1-R blockade with losartan on proton production from glucose metabolism and recovery of function in isolated working rat hearts perfused with Krebs-Henseleit buffer containing palmitate, glucose, and insulin. Aerobic perfusion (50 min) was followed by global, no-flow ischemia (30 min) and reperfusion (30 min) in the presence (n = 10) or absence (n = 14) of losartan (1 mumol/l) or the cardioprotective adenosine A1 receptor agonist N6-cyclohexyladenosine (CHA, 0.5 mumol/l, n = 11). During reperfusion in untreated hearts (controls), left ventricular (LV) minute work partially recovered to 38% of aerobic baseline, whereas proton production increased to 155%. Compared with controls, CHA improved recovery of LV work to 79% and reduced proton production to 44%. Losartan depressed recovery of LV work to 0% without altering proton production. However, exogenous ANG II (1-100 nmol/l) in combination with losartan restored recovery of LV work during reperfusion in a concentration-dependent manner, suggesting that postischemic recovery of function depends on intrinsic AT1-R stimulation.

Propofol and thiopental in a 1:1 volume mixture is chemically stable

Propofol and thiopental have been used clinically in combination for induction of anesthesia. Studies suggest that this mixture has synergistic activity, recovery characteristics similar to propofol alone, and bactericidal effects on multiple organisms. It may therefore be both clinically useful and cost-effective. In this study, we examined the chemical stability of this mixture. We used high-performance liquid chromatography to quantify the concentration of both propofol and thiopental in a given sample. This technique allows the detection of loss in total drug mass and of the appearance of breakdown products resulting from drug interaction. Ten samples of a 1:1 mixture by volume were prepared and assayed at Time 0 and Days 1, 3, and 7. Half the samples were incubated at 23 degrees C and the rest were stored at 4 degrees C. Other mixtures were assayed before and after filtration at Time 0 and Days 1 and 7 after storage at 23 degrees C. The assay was able to measure accurately the quantity of drug present in the samples. There was no significant decrease in the quantities of either propofol or thiopental in the mixture over the 7-day period. We conclude that the 1:1 volume mixture of propofol and thiopental is chemically stable for 1 wk at room temperature.

IMPLICATIONS

A mixture of propofol and thiopental has been used to induce anesthesia. We investigated the chemical stability of this mixture using high-performance liquid chromatography and found it to be stable for at least 24 h.

Peroxynitrite impairs cardiac contractile function by decreasing cardiac efficiency

Peroxynitrite (ONOO-) inhibits energy metabolism in isolated cells and mitochondria and may be involved in the depression of cardiac mechanical function during pathophysiological states. We determined the actions of ONOO- on cardiac function and energy metabolism in isolated working rat hearts and compared them with the NO donor S-nitroso-DL-acetylpenicillamine (SNAP). After a 15-min baseline aerobic perfusion, ONOO- (4 or 40 microM), SNAP (40 microM), or their vehicles were infused over a 60-min period. ONOO- or SNAP (40 microM each) caused a rapid and sustained rise in coronary flow. Infusion of 40 microM (but not 4 microM) ONOO- caused a marked depression in cardiac work with a delayed onset but no change in O2 consumption, resulting in a marked loss of cardiac efficiency. Cardiac work, O2 consumption, and cardiac efficiency remained constant in vehicle- and SNAP-treated hearts. ONOO- (40 microM) enhanced glycolysis and glucose oxidation but did not change pyruvate oxidation compared with its vehicle control, whereas SNAP was without effect. ONOO(-)-mediated depression in cardiac efficiency may be due to reduced coupling between ATP production and mechanical work.

Opposite effects of angiotensin AT1 and AT2 receptor antagonists on recovery of mechanical function after ischemia-reperfusion in isolated working rat hearts

BACKGROUND

Angiotensin II type 1 (AT1) receptor antagonists, when given over the long term, reduce the deleterious consequences of ischemia-reperfusion injury. Whether short-term administration of AT1 or angiotensin II type 2 (AT2) receptor antagonists is cardioprotective has not been investigated.

METHODS AND RESULTS

The effects of short-term administration of selective AT1 and AT2 receptor antagonists on the recovery of mechanical function during reperfusion after 30 minutes of global, no-flow ischemia were studied in left atrium-perfused isolated working rat hearts. Control hearts (n = 8) showed incomplete recovery of left ventricular minute work (LV work) and cardiac efficiency during reperfusion to 51 +/- 15% and 61 +/- 19% of preischemic levels, respectively. Compared with control hearts, the selective AT2 receptor antagonist PD123,319 (0.3 mumol/L) given before ischemia (n = 7) improved the recovery of LV work and efficiency to 82 +/- 4% and 98 +/- 7% of preischemic levels, respectively (P < .01). In contrast, the selective AT1 antagonist losartan (1 mumol/L) blocked the recovery of LV work and depressed efficiency to 0 +/- 0% and 1 +/- 0% (n = 7) of preischemic levels, respectively (P < .01; n = 7). Neither antagonist altered coronary vascular conductance.

CONCLUSIONS

This is the first demonstration that short-term treatment with a selective AT1 versus AT2 antagonist exerts different effects on recovery of mechanical function after ischemia-reperfusion: the AT2 antagonist was cardioprotective, whereas the AT1 antagonist was not. These data suggest that AT2 antagonists and AT1 agonists may offer novel approaches for the treatment of mechanical dysfunction after ischemia-reperfusion.

Antecedent ischemia reverses effects of adenosine on glycolysis and mechanical function of working hearts

This study compared the effects of adenosine (Ado) on the coupling of glycolysis and glucose oxidation and on mechanical function in normal hearts and in hearts subjected to transient ischemia. Isolated working rat hearts were perfused with Krebs containing 1.2 mM palmitate and 100 microU/ml insulin. After 15 min of aerobic perfusion, hearts underwent either two cycles of 10 min of ischemia and 5 min of reperfusion (stressed) or 30 min of aerobic perfusion (control). After 45 min, hearts underwent either aerobic perfusion for 35 min (series A) or 30 min of ischemia and 30 min of reperfusion (series B). In series A, left ventricular minute work (LV work) was similar in control and stressed hearts and was not affected by Ado (500 microM) or N6-cyclohexyladenosine (CHA 0.5 microM). Ado reduced glycolysis by 49% in control hearts but increased glycolysis by 74% in stressed hearts. CHA inhibited glycolysis in both groups by 50 and 62%, respectively. In series B, LV work during reperfusion recovered to a similar extent in untreated control and stressed hearts. In control hearts, Ado reduced glycolysis by 50% while enhancing LV work to 81% of preischemic values. In stressed hearts, Ado increased glycolysis by 34% and depressed LV work to 9%, whereas CHA inhibited glycolysis by 53% and LV work to 91%. These data indicate that coupling of glycolysis to glucose oxidation is a key determinant of mechanical function of the postischemic myocardium. They also show that the metabolic and protective effects of Ado depend on the status of the heart before sustained ischemia.

Cardiac efficiency is improved after ischemia by altering both the source and fate of protons

Cardiac efficiency is decreased in hearts after severe ischemia. We determined whether reducing the production of H+ from glucose metabolism or inhibiting the clearance of H+ via Na(+)-H+ exchange could increase cardiac efficiency during reperfusion. This was achieved using dichloroacetate (DCA) to stimulate glucose oxidation and 5-(N,N-dimethyl)-amiloride (DMA) to inhibit Na(+)-H+ exchange, respectively. Isolated working rat hearts were subjected to 30 minutes of global ischemia and 60 minutes of reperfusion. Glycolysis and oxidation rates of glucose, lactate, and palmitate were measured. Recovery of cardiac work, O2 consumption (MVO2), and rates of acetyl-coenzyme A and ATP production during reperfusion were determined. After ischemia, cardiac work recovered to 35 +/- 5% of preischemic values in control hearts (n = 23), although MVO2, tricarboxylic acid (TCA) cycle activity, and ATP production from glycolysis and oxidative metabolism rapidly recovered to preischemic levels. This decrease in cardiac efficiency was accompanied by a substantial production of H+ from glucose metabolism DCA caused a 2.2-fold increase in glucose oxidation, a 46 +/- 17% decrease in H+ production, a 1.6-fold increase in cardiac efficiency, and a 2.0-fold increase in cardiac work during reperfusion (n = 17). Inhibition of Na(+)-H+ exchange with DMA did not alter TCA cycle activity and ATP production rates but did result in a 1.8-fold increase in cardiac efficiency and a 1.7-fold increase in cardiac work (n = 12). These data show that cardiac efficiency and the contractile function after ischemia can be improved by either reducing the rate of H+ production from glucose metabolism during reperfusion or inhibiting the clearance of H+ via Na(+)-H+ exchange. Our data suggest that an increased requirement for ATP to restore ischemia-reperfusion-induced alterations in ion homeostasis contributes to the decrease in cardiac efficiency and contractile function after ischemia.

Characterization of 5'AMP-activated protein kinase activity in the heart and its role in inhibiting acetyl-CoA carboxylase during reperfusion following ischemia

Despite the high expression of 5'AMP activated protein kinase (AMPK) in heart, the activity and function of this enzyme in heart muscle has not been characterized. We demonstrate that rat hearts have a high AMPK activity, comparable to that found in liver, which could be stimulated up to 3-fold by 5'AMP. Cardiac AMPK is also under phosphorylation control, since in vitro incubation of cardiac AMPK with protein phosphatase 2A completely abolished activity, while incubation with ATP/Mg(2+) resulted in over a 2-fold increase in activity. To investigate the function of AMPK in heart muscle, isolated working rat hearts were subjected to 30 min of global no-flow ischemia, followed by 60 min of aerobic reperfusion. AMPK activity was increased in heart at the end of reperfusion compared to aerobic controls (379 +/- 53 (n=5) vs. 139 +/- 19 (n=5) pmol x min(-1) x mg protein(-1), P<0.05, respectively). Treatment of AMPK in vitro with protein phosphatase 2A reversed this activation. Since AMPK can phosphorylate and inactivate acetyl-CoA carboxylase (ACC) in other tissues, and heart ACC has an important role in regulating fatty acid oxidation, we measured ACC activity in hearts reperfused post-ischemia. ACC activity was decreased at the end of reperfusion compared to aerobic controls (3.64 +/- 0.36 (n=9) vs. 10.93 +/- 0.60 (n=11) nmol x min(-1) x mg protein(-1), respectively, P<0.05). A significant negative correlation (r= -0.78) was observed between AMPK activity and ACC activity measured in aerobic and reperfused ischemic hearts. Low ACC activity could be reversed if ACC was extracted from hearts in the absence of phosphatase inhibitors, suggesting that phosphorylation of ACC decreased enzyme activity. This suggests that following ischemia AMPK is phosphorylated and activated (possibly by an AMPK kinase). AMPK then phosphorylates and inactivates ACC. The resultant decrease in malonyl-CoA levels could explain the acceleration of fatty acid oxidation that is observed during reperfusion of ischemic hearts.

Inhibition of glycolysis and enhanced mechanical function of working rat hearts as a result of adenosine A1 receptor stimulation during reperfusion following ischaemia

1. This study examined effects of adenosine and selective adenosine A1 and A2 receptor agonists on glucose metabolism in rat isolated working hearts perfused under aerobic conditions and during reperfusion after 35 min of global no-flow ischaemia. 2. Hearts were perfused with a modified Krebs-Henseleit buffer containing 1.25 mM Ca2+, 11 mM glucose, 1.2 mM palmitate and insulin (100 muu ml-1), and paced at 280 beats min-1. Rates of glycolysis and glucose oxidation were measured from the quantitative production of 3H2O and 14CO2, respectively, from [5-3H/U-14C]-glucose. 3. Under aerobic conditions, adenosine (100 microM) and the adenosine A1 receptor agonist, N6-cyclohexyladenosine (CHA, 0.05 microM), inhibited glycolysis but had no effect on either glucose oxidation or mechanical function (as assessed by heart rate systolic pressure product). The improved coupling of glycolysis to glucose oxidation reduced the calculated rate of proton production from glucose metabolism. The adenosine A1 receptor antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX 0.3 microM) did not alter glycolysis or glucose oxidation per se but completely antagonized the adenosine- and CHA-induced inhibition of glycolysis and proton production. 4. During aerobic reperfusion following ischaemia, CHA (0.05 microM) again inhibited glycolysis and proton production from glucose metabolism and had no effect on glucose oxidation. CHA also significantly enhanced the recovery of mechanical function. In contrast, the selective adenosine A2a receptor agonist, CGS-21680 (1.0 microM), exerted no metabolic or mechanical effects. Similar profiles of action were seen if these agonists were present during ischaemia and throughout reperfusion or when they were present only during reperfusion. 5. DPCPX (0.3 microM), added at reperfusion, antagonized the CHA-induced improvement in mechanical function. It also significantly depressed the recovery of mechanical function per se during reperfusion. Both the metabolic and mechanical effects of adenosine (100 microM) were antagonized by the nonselective A1/A2 antagonist, 8-sulphophenyltheophylline (100 microM). 6. These data demonstrate that inhibition of glycolysis and improved recovery of mechanical function during reperfusion of rat isolated hearts are mediated by an adenosine A1 receptor mechanism. Improved coupling of glycolysis and glucose oxidation during reperfusion may contribute to the enhanced recovery of mechanical function by decreasing proton production from glucose metabolism and the potential for intracellular Ca2+ accumulation, which if not corrected leads to mechanical dysfunction of the postischaemic myocardium.

Uncoupling of contractile function from mitochondrial TCA cycle activity and MVO2 during reperfusion of ischemic hearts

In this study we determined whether contractile function becomes uncoupled during reperfusion of ischemic hearts from mitochondrial tricarboxylic acid (TCA) cycle activity or myocardial O2 consumption (MVO2). Isolated working rat hearts perfused with buffer containing 1.2 mM palmitate and 11 mM glucose were subjected to 30 min of global ischemia followed by 60 min of aerobic reperfusion. During reperfusion, cardiac work recovered to 26.5 +/- 5.4% (n = 29) of preischemic levels, even though TCA cycle activity, fatty acid beta-oxidation, glucose oxidation, glycolysis, and MVO2 rapidly recovered. As a result, the efficiency of coupling between cardiac work and TCA cycle activity and between cardiac work and mitochondrial respiration decreased during reperfusion. In contrast, coupling of TCA cycle activity to MVO2 during reperfusion recovered to preischemic values. Addition of 1 mM dichloroacetate at reperfusion resulted in a significant increase in both cardiac work and cardiac efficiency during reperfusion. This was associated with a significant decrease in H+ production due to an improved balance between glycolysis and glucose oxidation. These data demonstrate that mitochondrial function and overall myocardial ATP production quickly recover in rat hearts after a 30-min period of global ischemia. However, mitochondrial ATP production is not efficiently translated into mechanical work during reperfusion. This may be due to an imbalance between glycolysis and glucose oxidation, resulting in an increase in H+ production and a decrease in cardiac efficiency.

Ischemic preconditioning inhibits glycolysis and proton production in isolated working rat hearts

The effect of ischemic preconditioning (IPC) on glycolysis, glucose oxidation, adenine nucleotide and nucleoside levels, and mechanical function was studied in isolated paced working rat hearts under aerobic conditions or when reperfused following sustained ischemia. IPC inhibited glycolysis in aerobic hearts (4.48 +/- 0.66 vs. 3.18 +/- 0.39 mumol.min-1.g dry wt-1) and calculated proton production attributable to exogenous glucose (7.79 +/- 1.31 vs. 4.73 +/- 0.81 mumol.min-1.g dry wt-1). In hearts subjected to ischemia and reperfusion, IPC decreased, relative to controls, glycogen content before the onset of ischemia (116.6 +/- 4.3 vs. 158.0 +/- 8.4 mumol/dry wt) and decreased consumption of glycogen during ischemia (54 +/- 6 vs. 76 +/- 7 mumol/dry wt). During reperfusion, glycolysis was lower in IPC hearts (2.45 +/- 0.16 vs. 4.4 +/- 0.46 mumol.min-1.g dry wt-1), as was calculated proton production (3.57 +/- 0.30 vs. 8.38 +/- 0.93 mumol.min-1.g dry wt-1). Glucose oxidation was similar in control and IPC hearts. Adenosine and ATP content of IPC hearts, relative to controls, were higher at the end of ischemia, being 0.86 +/- 0.08 vs. 0.34 +/- 0.15 mumol/g dry wt and 11.3 +/- 0.8 vs. 5.0 +/- 1.6 mumol/g dry wt, respectively. IPC enhanced recovery of ventricular work during reperfusion of ischemic hearts from 37 to 68%. These results indicate that IPC is associated with a reduction in glycogen content, inhibition of glycolysis during ischemia and reperfusion, and a decrease in proton production from glucose. These changes may, in part, explain the enhanced recovery of mechanical function observed in IPC hearts.

Evaluation of a long-range adaptive predictive controller for computerized drug delivery systems

A closed-loop adaptive control system, based on the generalized predictive control law with a terminal matching condition, has been developed for computerized drug delivery. The control law is a minimization of the squares of prediction errors over a small future prediction horizon plus weighted square of the prediction error at steady-state. A control-relevant, long-range identification algorithm is used for on-line parameter estimation. Since the control and identification are mutually compatible, the system truly satisfies the approximate dual control criterion. The system has been applied to the control of mean arterial pressure (MAP) by automatic infusion of sodium nitroprusside in the presence of physical and physiological constraints. Experimental evaluation on six mongrel dogs, in an ethics-approved manner, included setpoint tracking and regulation of MAP in the presence of unpredictable disturbances. The system was found to be capable of inducing hypotension in an average of 2.44 +/- 0.31 min (mean +/- standard error of mean) after probing without any overshoots in mean arterial pressure. The nitroprusside infusion was also free of any ringing. When the subjects were not disturbed, 96.2% of mean arterial pressure remained within 5 mm Hg of the target pressure. A series of disturbances introduced in the presence and absence of closed-loop control affirms the robustness and effectiveness of this control system.

Adenosine alters glucose use during ischemia and reperfusion in isolated rat hearts

BACKGROUND

Adenosine possesses marked cardioprotective properties, but the mechanisms for this beneficial effect are unclear. The objective of this study was to determine the effect of adenosine given before ischemia or at reperfusion on mechanical function, glucose oxidation, glycolysis, and metabolite levels in isolated, paced (280 beats per minute) working rat hearts.

METHODS AND RESULTS

Hearts were perfused with Krebs-Henseleit buffer containing 11 mM glucose, 1.2 mM palmitate, and 500 microU.mL-1 insulin at an 11.5 mm Hg left atrial preload and 80 mm Hg aortic afterload. Adenosine (100 microM) pretreatment or adenosine (100 microM) at reperfusion markedly increased the recovery of mechanical function (from 44% to 81% and 96%, respectively) after 60 minutes of low-flow ischemia (coronary flow, 0.5 mL.min-1). Glucose oxidation (mumol.min-1 x g dry wt-1) was inhibited during ischemia (from 0.44 +/- 0.04 to 0.12 +/- 0.01), and this was not altered by adenosine (100 microM). During reperfusion, glucose oxidation recovered (to 0.38 +/- 0.02) and adenosine (100 microM), given at reperfusion, further increased glucose oxidation (to 0.52 +/- 0.06). The rate of glycolysis (mumol.min-1 x g dry wt-1), which was unaffected by ischemia per se, was inhibited by adenosine pretreatment (from 4.7 +/- 0.3 to 2.6 +/- 0.3). During reperfusion, glycolysis was also inhibited by adenosine relative to control (3.9 +/- 0.8) either when present during ischemia (2.6 +/- 0.6) or during reperfusion (1.4 +/- 0.4). These effects of adenosine on glucose metabolism reduced the calculated rate of H+ production attributable to glucose metabolism during the ischemic and reperfusion periods. Tissue lactate levels (mumol.g dry wt-1), which increased during ischemia (from 9.3 +/- 1.1 to 87.4 +/- 10.3) and then declined during reperfusion (to 26.2 +/- 3.7), were depressed further by adenosine pretreatment (to 19.7 +/- 4.1) and by adenosine at reperfusion (to 13.6 +/- 2.1). ATP levels (mumol.g dry wt-1), which were depressed by ischemia (from 18.1 +/- 1.1 to 10.6 +/- 1.3) and tended to be further depressed during reperfusion (to 7.1 +/- 0.7), were increased by adenosine pretreatment (to 14.1 +/- 1.2) and by adenosine at reperfusion (to 15.6 +/- 2.4).

CONCLUSIONS

The effects of adenosine on glucose metabolism that would tend to decrease cellular acidosis and hence, Ca2+ overload, may explain the beneficial effects of adenosine on mechanical function observed in these hearts during reperfusion after ischemia.

Cardiovascular selectivity of adenosine receptor agonists in anaesthetized dogs

1. In order to determine the relevance of adenosine (Ado) receptor classification obtained from in vitro methods to the cardiovascular actions of Ado agonists in vivo, the cardiovascular effects of adenosine 5'-monophosphate (AMP), N6-cyclohexyladenosine (CHA, 400 fold A1-selective), 5'-N-ethyl-carboxamidoadenosine (NECA, A1 approximately A2) and 2-phenylaminoadenosine (PAA, 5 fold A2-selective) were compared in open-chest, fentanyl-pentobarbitone anaesthetized dogs. 2. Graded doses of CHA (10 to 1000 micrograms kg-1), NECA (0.5 to 100 micrograms kg-1) or PAA (0.1 to 20 micrograms kg-1) were administered intravenously and changes in haemodynamics and myocardial contractility were assessed 10 min following each dose. The effects of graded infusions of AMP (200 to 1000 micrograms kg-1 min-1) were also evaluated. 3. AMP and each of the Ado analogues (NECA > PAA > CHA) increased the systemic vascular conductance index (SVCI) in a dose-dependent manner and reduced mean arterial pressure (MAP). At doses causing similar increases in SVCI, these agonists caused (i) similar reflex increases in heart rate (HR) and cardiac index (CI) and decreases in AV conduction interval (AVi) and (ii) similar increases in coronary vascular conductance (CVC). 4. After cardiac autonomic blockade with atropine (0.2 mg kg-1) and propranolol (1 mg kg-1), AMP, CHA and PAA still increased SVCI and CVC and decreased MAP. CHA and PAA had no marked effects on HR, CI or AVi. As in the absence of cardiac autonomic blockade, equieffective vasodilator doses of CHA and PAA had identical effects on CVC, CI and AVi. 5.Myocardial contractility, as assessed by E,,,,, measurements, was stimulated by AMP in control animals. Following cardiac autonomic blockade, PAA increased contractility while AMP and CHA had no significant effects.6. Despite marked.differences in receptor selectivity in vitro, no marked differences between the actions of these Al- and A2-selective Ado receptor agonists on the cardiovascular system in vivo were apparent.Difficulties therefore exist in the application of in vitro Ado receptor selectivity data to the prediction of the cardiovascular effects of Ado agonists in vivo.

Enhancement of bupivacaine toxicity by diltiazem in anaesthetized dogs

We have studied the cardiovascular effects of graded doses of bupivacaine in the absence or presence of clinical concentrations (approximately 250 micrograms litre-1) of diltiazem in fentanyl-pentobarbitone anaesthetized dogs. Bupivacaine was given, increasing in a stepwise manner, as a loading dose (200, 400 or 600 micrograms kg-1) followed by a 30-min i.v. infusion (25, 100 or 200 micrograms kg-1 min-1, respectively). Thereafter, bupivacaine was infused at 400 micrograms kg-1 min-1 until each animal died. Group A (n = 7) received bupivacaine, group B (n = 5) diltiazem (400 micrograms kg-1 followed by 12 micrograms kg-1 min-1) and group C (n = 7) received diltiazem followed by bupivacaine given as in group A. Lethal plasma concentrations of bupivacaine were significantly smaller (P < 0.01) in group C (7.1 (SEM 0.7) vs 12.6 (1.5) mg litre-1). Bupivacaine produced similar decreases in cardiac index, left ventricular (LV) segmental work and the first derivative of LV pressure (LV dP/dt) in the absence and presence of diltiazem. In group A, bupivacaine increased systemic vascular resistance index (SVRI) and thus mean arterial pressure (MAP) was maintained. In group C, SVRI, reduced by diltiazem per se, did not increase in response to bupivacaine, so MAP was not maintained. Death resulted from a progressive decrease in cardiac contractility and MAP. Plasma concentrations of bupivacaine attained at the three doses were similar in the absence and presence of diltiazem. This study has shown that the toxicity of bupivacaine was increased approximately two-fold by diltiazem.

Adenosine modification of energy substrate use in isolated hearts perfused with fatty acids

The objective of this study was to determine the effect of adenosine on overall myocardial substrate utilization and mechanical function in isolated working rat hearts. Hearts were perfused with Krebs-Henseleit buffer containing 11 mM glucose (no fat) or with 11 mM glucose and 0.4 mM palmitate (normal fat). Steady-state rates of glycolysis, glucose oxidation, and fatty acid oxidation were measured by determination of quantitative 3H2O and 14CO2 production from radiolabeled substrates. The ratio of glycolysis (6.07 +/- 0.57 mumol.min-1.g dry wt-1) to glucose oxidation (3.12 +/- 0.28 mumol.min-1.g dry wt-1) under no fat conditions was 2:1. The addition of palmitate per se decreased glucose oxidation (to 0.81 +/- 0.09 mumol.min-1.g dry wt-1) and increased the glycolysis-to-glucose oxidation ratio to 6:1. Adenosine (100 microM) reduced this ratio to 3:1 by decreasing glycolysis (to 3.75 +/- 0.32 mumol.min-1.g dry wt-1) and increasing glucose oxidation (to 1.28 +/- 0.18 mumol.min-1.g dry wt-1) in the presence of palmitate. Steady-state palmitate oxidation rates were not altered by adenosine. Adenosine increased efficiency (work performed per unit O2 consumed) of spontaneously beating hearts but had no effect in paced hearts. These effects of adenosine on glucose metabolism may explain the beneficial actions of adenosine during reperfusion post ischemia.

Adenosine receptors and nucleoside transport sites in cardiac cells

1. Potential mechanisms responsible for the prominent depression of atrioventricular conduction by adenosine have been investigated in guinea-pig heart. 2. Adenosine A1 receptors and nucleoside transport (NT) sites were identified and enumerated in cardiac myocytes, atrioventricular conduction cells and coronary endothelial cells in 10 microns sections by autoradiographical analysis of the binding of the A1 selective antagonist 8-cyclopentyl-1,3-[3H]-dipropylxanthine ([3H]-DPCPX) and the NT ligand [3H]-nitrobenzylthioinosine ([3H]-NBMPR), respectively. 3. Atrioventricular conduction cells were identified by acetylcholinesterase histochemistry and endothelial cells by von Willebrand factor immunohistochemistry. 4. Site-specific binding of [3H]-DPCPX, when expressed as grains per cell nucleus was significantly higher (30 fold) in conduction cells than in surrounding myocytes. [3H]-DPCPX site density on endothelial cells in adjacent coronary vessels was not significantly different from myocytes. 5. In contrast, autoradiography of [3H]-NBMPR sites in these areas indicated that, relative to myocytes, conduction cells and endothelial cells were significantly enriched (2 fold and 4.5 fold, respectively) in NT sites. 6. The pronounced dromotropic effect of adenosine in guinea-pig heart is correlated with a higher density of adenosine A1 receptors in atrioventricular conduction cells than in myocytes. The NT capacity of these cells, as estimated by [3H]-NBMPR binding site density, is not increased in proportion to A1 receptors.

Comparison of the haemodynamic effects of adenosine monophosphate with sodium nitroprusside in a canine model of acute global left ventricular dysfunction

1. The haemodynamic effects of adenosine 5'-monophosphate (AMP) and sodium nitroprusside (SNP) were compared in anaesthetized dogs following the induction of acute left ventricular (LV) dysfunction. 2. LV dysfunction was induced by the intracoronary administration of glass microbeads until left ventricular end diastolic pressure (LVEDP) was increased from 5 to 15 mmHg. This was associated with a decrease in LV dP/dt and cardiac index (CI) of 30% and 27%, respectively, and an increase in systemic vascular resistance index (SVRI) of 37%. 3. Graded doses of AMP (100 to 1000 micrograms kg-1 min-1) or SNP (1 to 10 micrograms kg-1 min-1) reduced SVRI and increased CI in a dose-related manner. Heart rate was not altered by either agent. At doses that caused similar reductions in SVRI, CI was increased more by AMP than by SNP. 4. The mechanisms responsible for the greater elevation of CI by AMP relative to SNP may be related to its more selective arterial vasodilator activity. SNP reduced cardiac preload that limited the expected increase in CI. 5. The haemodynamic profile of AMP suggests that it may be useful in the pharmacological management of acute cardiac failure, either when used alone or in combination with positive inotropic agents and/or selective venodilators.

Gallbladder contractility and gallstone formation in the Richardson Ground Squirrel

The pathogenesis of cholesterol cholelithiasis in man is probably multifactorial and the mechanism by which gallbladder stasis occurs in gallstone patients has not been studied in detail. In the present study, time-dependent changes in gallbladder motility of the Richardson Ground Squirrels were investigated. 100 of animals were examined for their contractile responses of gallbladders to CCK-OP and Ach in vitro. Also, biochemical changes of serum and bile were investigated. There were no significant differences in motility of gallbladders to CCK-OP or Ach between control and cholesterol-fed animals. The results of this study indicate that gallbladder muscle contractility remains unchanged during the dietary induction of cholesterol gallstones in the Richardson Ground Squirrel.

Comparison of hemodynamic changes induced by adenosine monophosphate and sodium nitroprusside alone and during dopamine infusion in the anesthetized dog

Adenosine receptor stimulation, such as by adenosine monophosphate (AMP), elicits systemic vasodilation that may be useful to control cardiac afterload during treatment of acute low-output cardiac failure. This study compared the hemodynamic effects of graded doses of sodium nitroprusside (SNP) with those of AMP when infused alone or in combination with the positive inotropic agent dopamine (DA) in anesthetized dogs. Both SNP (2-25 micrograms.kg-1.min-1) and AMP (200-2500 micrograms.kg-1.min-1) were effective vasodilators and reduced systemic vascular resistance and arterial pressure in a dose-dependent manner. Heart rate and cardiac index were increased by both agents. When compared at dosages that caused similar decreases in arterial pressure, cardiac index was increased more by AMP than by SNP. Also, AMP-induced vasodilation was associated with less tachyphylaxis. Sodium nitroprusside and AMP, at the dosages used, did not depress atrioventricular nodal conduction or antagonize DA-induced increases in renal blood flow. At equivalent decreases in mean arterial pressure, the increase from baseline in cardiac and stroke indices observed with AMP alone was further increased by the concomitant administration of DA. These results suggest that AMP and DA-AMP may offer significant advantages over SNP or DA-SNP in situations where elevation of cardiac output and reduction in afterload are required.

Heterogeneity of nucleoside transport inhibitory sites in heart: a quantitative autoradiographical analysis

1. The distribution of nucleoside transport inhibitory sites in rat and guinea-pig cardiac sections was investigated by use of [3H]-nitrobenzylthioinosine ([3H]-NBMPR) autoradiography. The distribution of these sites was heterogeneous in guinea-pig sections and homogeneous in rat sections. 2. The areas of high density of nucleoside transport inhibitory sites found in guinea-pig cardiac sections were compared to the distribution of an endothelial cell marker, von Willebrand Factor, determined by radioimmunocytochemistry. These two markers were co-localized suggesting that coronary endothelial cells from guinea-pig have a high density of NBMPR binding sites and thus may have a high nucleoside transport capacity. 3. Nucleoside transporter subtypes with differing affinity for NBMPR or dipyridamole were investigated by quantitative autoradiography. Sites in rat tissues had high affinity for NBMPR (KD = 0.6 nM) but were of low sensitivity to dipyridamole (Ki = 3.1 microM). In guinea-pig sections, areas of high and low [3H]-NBMPR binding site density were analyzed separately. In both areas, sites had high affinity for NBMPR (KD = 1.4 nM, 4.5 nM, respectively) and dipyridamole (Ki = 108 nM, 245 nM, respectively). 4. While differences in density of nucleoside transport inhibitory sites are detectable between distinct regions of the heart, subtypes differing in affinity for NBMPR or dipyridamole were not evident. Therefore, more detailed structure activity studies are required to determine if subtypes of these sites exist within a single heart.

Subtypes of nucleoside transport inhibitory sites in heart: a quantitative autoradiographical analysis

We evaluated the interaction of several nucleoside transport inhibitors and substrates with the binding of [3H]nitrobenzylthioinosine ([3H]NBMPR) to nucleoside transport sites in guinea pig cardiac sections. Using quantitative autoradiography, we determined inhibition constants for inhibition of [3H]NBMPR binding to both coronary endothelial cells and cardiac myocytes. We studied the interactions of NBMPR, nitrobenzylthioguanosine, dipyridamole, dilazep, hexobendine, lidoflazine, mioflazine, soluflazine, adenosine, inosine and uridine for these two cell types. Of the compounds tested in this study, lidoflazine (8.2X) and hexobendine (6.3X) have the greatest selectivity for coronary endothelial cell nucleoside transporters. All other compounds had 3-fold or less selectivity. Therefore, there is evidence of nucleoside transporter subtypes between endothelial cells and myocytes. This heterogeneity of transport inhibitory sites on nucleoside transporters may allow the development of agents to modulate selectively some of the cardiovascular effects of adenosine.

Some pharmacological activities of novel adenine-related compounds isolated from a marine sponge Agelas mauritiana

Agelasimine A and agelasimine B, two novel compounds related to adenine, have been isolated from the orange sponge, Agelas mauritiana, and have been tested for a variety of biological activities. Both compounds inhibited proliferation of cultured L1210 leukemia cells at nanomolar concentrations with accumulation in the G1 stage of the cell cycle. However, no prolongation of life was observed in mice bearing P388 leukemia treated with these compounds. In the rat isolated aorta, micromolar concentrations of agelasimines were very effective in inhibiting contractions elicited by potassium chloride but had little or no effect on responses for prostaglandin F2 alpha and had modest effects on the responses to noradrenaline and significant effects on 5-hydroxytryptamine. Agelsamines A and B appeared to be equipotent in causing relaxation in rabbit jejunum and bovine coronary artery, and they also inhibited nucleoside transport into rabbit erythrocytes in micromolar concentrations.

5'-Deoxy-5'-methylthioadenosine: a nucleoside which differentiates between adenosine receptor types

The activities of an endogenous nucleoside, 5'-deoxy-5'-methylthioadenosine (MTA), on adenosine sensitive sites such as adenosine A1 and A2 receptors and the P-site, as well as on purine nucleoside transport, have been studied. This nucleoside competitively antagonized the A2 receptor-mediated stimulation of neuroblastoma adenylate cyclase, produced a GTP-dependent and 8-p-sulfophenyltheophylline-sensitive inhibition of adenylate cyclase activity in rat cerebellar membranes, and decreased the spontaneous contractile activity of isolated segments of rabbit jejunum. MTA was neither active at the P-site nor did it diminish the binding of [3H]nitrobenzylthioinosine, a nucleoside transport inhibitor. We conclude that (a) MTA is an agonist at the adenosine A1 receptor but an antagonist at the A2 receptor, and (b) the adenosine receptor which causes relaxation of rabbit jejunum is not a neuroblastoma-type A2 receptor which activates adenylate cyclase.

Periodic gallbladder contraction maintains bile acid circulation during the fasting period: a canine study

Using a canine model we have studied the relationship between the interdigestive cycle in the small intestine, motility changes in the biliary tract and bile acid output into the duodenum from direct hepatic secretion and gallbladder emptying. Under anaesthesia catheters were inserted into the gallbladder, common bile duct and duodenum, and electrodes were attached to the small intestine in five dogs. These animals were subsequently studied conscious and fasting. A double marker technique was used to measure bile acid output from the gallbladder and liver while pressure in the gallbladder and common bile duct and electrical activity in the small intestine were monitored. Four complete interdigestive cycles were recorded in each dog. Output of bile acids from the gallbladder fluctuated with the phases of the cycle: being lowest in phase I (3.9 +/- 0.7 mumol/min); increasing significantly (P less than 0.005) in phase II (9.8 +/- 1.0 mumol/min); remaining elevated in phase III (13.9 +/- 1.7 mumol/min); and falling significantly (P less than 0.05) in phase IV (8.4 +/- 1.8 mumol/min). In contrast, hepatic secretion of bile acids directly into the duodenum remained fairly constant. Intraluminal pressure in the biliary tract paralleled the fluctuation in gallbladder bile acid output, being significantly increased (P less than 0.05) in phases II and III. Periodic contraction of the gallbladder would, therefore, appear to be the principal mechanism for the phasic output of bile during fasting.

Contractility of human gallbladder muscle in vitro

This study examined the effects of transmural nerve stimulation, acetylcholine, adrenoceptor agonists and several peptides on the contractility of strips of human gallbladder in vitro. Acetylcholine caused concentration-related contractions of the tissues and the sensitivity to acetylcholine was similar in gallbladders with mild and severe chronic cholecystitis. Noradrenaline and adrenaline relaxed gallbladder strips, probably via beta 2-adrenoceptor stimulation. Transmural nerve stimulation always caused contractions, but in the presence of atropine inhibitory responses were demonstrable and these were antagonized by propranolol. There was no evidence of non-adrenergic inhibitory neural responses. Of the peptides tested, only cholecystokinin octapeptide (CCK-OP), gastrin, pentagastrin, substance P and caerulein caused contractions. Responses to CCK-OP, gastrin and pentagastrin were antagonized by dibutyryl cyclic GMP. Hormones which had no effect upon human gallbladder strips included motilin, secretin, bombesin, neurotensin, glucagon, vasopressin, VIP and somatostatin. Considerable differences therefore exist between human tissues and those from experimental animals with respect to the direct actions of neural and hormonal stimuli on gallbladder contractility.

Nucleoside transport in guinea pig myocytes. Comparison of the affinities and transport velocities for adenosine and 2-chloroadenosine

The affinities of adenosine and 2-chloroadenosine for the nucleoside transport system of guinea pig myocytes were evaluated indirectly by studying the inhibition of the binding of [3H]nitrobenzylthioinosine and directly by measuring the influx of [3H]radiolabeled substrates. Maximal transport velocities of the two nucleosides were also obtained. [3H]Nitrobenzylthioinosine bound to a single class of high-affinity sites (KD of 0.8 nM) which possessed a maximal binding capacity (Bmax) of 870,000 sites/cell. Adenosine, 2-chloroadenosine or the nucleoside transport inhibitor, dipyridamole, competitively inhibited the site-specific binding of [3H]nitrobenzylthioinosine with Ki values of 318 microM, 22 microM and 75 nM respectively. Both [3H]adenosine and [3H]2-chloroadenosine entered myocytes in a saturable and inhibitible manner. Observed transport kinetic constants (Km and Vmax) were 146 microM and 24.2 pmoles/10(6) cells/sec, respectively, for adenosine and 36 microM and 11.7 pmoles/10(6) cells/sec, respectively for 2-chloroadenosine. Affinities of adenosine, 2-chloroadenosine, nitrobenzylthioinosine and dipyridamole for the nucleoside transport system derived from binding and influx methodologies were equivalent which confirms that [3H]nitrobenzylthioinosine binding sites are closely associated with the nucleoside transporter.

Nitrobenzylthioinosine: an in vivo inhibitor of pig erythrocyte energy metabolism

The potential role of plasma nucleosides as metabolic energy substrates for pig erythrocytes, which are impermeable to glucose, was investigated in vivo by infusion of anesthetized pigs with nitrobenzylthioinosine phosphate (NBMPR-P), a soluble prodrug form of the specific nucleoside transport inhibitor, nitrobenzylthioinosine. NBMPR-P administration (1 or 10 mg X kg-1 X h-1) led to complete in vivo blockade of erythrocyte nucleoside transport activity and was associated with a dramatic decrease in the erythrocyte [ATP]-to-[ADP] ratio from 11.4 at time 0 to 2.9 after 4 h (mean results from 3 animals). Plasma inosine concentrations increased progressively from 2-4 microM at time 0 to 20-70 microM after 4 h of drug administration. In contrast, plasma adenosine concentrations remained less than 0.4 microM in all samples. These data suggest that pig erythrocytes utilize plasma inosine as their physiological energy substrate.

Affinity of calcium channel inhibitors, benzodiazepines, and other vasoactive compounds for the nucleoside transport system

There is evidence to suggest that several different groups of drugs including the so-called coronary vasodilators, benzodiazepines, and calcium channel inhibitors may owe their vasoactivity, in part, to the potentiation of the vasorelaxant effects of endogenous adenosine. To measure the affinity of some of these agents for the membrane-located nucleoside transport system, competition binding assays have been performed using the high-affinity radioligand [3H]nitrobenzylthioinosine (NBMPR). Experiments were performed on human erythrocytes and cardiac membranes from guinea pigs and rats. Recognized nucleoside transport inhibitors had high affinity (less than 50 nM) for NBMPR recognition sites associated with the nucleoside transporter complex in human erythrocytes, whereas calcium channel inhibitors and benzodiazepines had predominantly low affinity (greater than 1 microM). Although some recognized transport inhibitors, such as dipyridamole, show marked differences in affinity for NBMPR sites in guinea pig and rat tissues, benzodiazepines and calcium channel blockers displayed no such species selectivity and had low affinity (greater than 1 microM) for NBMPR sites in both guinea pig and rat cardiac membranes. Consequently, it is unlikely that agents such as benzodiazepines and calcium channel inhibitors cause significant inhibition of adenosine transport, and hence potentiate adenosine actions, at the concentrations required to induce effects through occupation of their respective, specific high-affinity sites.

Species differences in the binding of [3H]nitrobenzylthioinosine to the nucleoside transport system in mammalian central nervous system membranes: evidence for interconvertible conformations of the binding site/transporter complex

The binding of [3H]nitrobenzylthioinosine (NBMPR) to specific sites in CNS membranes was investigated using cortical tissue from a variety of mammalian species. Mass law analysis of the site-specific binding of NBMPR data revealed that rat, mouse, guinea pig, and dog cortical membranes each contained an apparent single class of high-affinity (KD 0.11-4.9 nM) binding sites for NBMPR; rabbit cortical membranes, however, exhibited two distinct classes of NBMPR binding sites with KD values of 0.4 nM and 13.8 nM. Dipyridamole, a potent inhibitor of nucleoside transport, produced a biphasic profile of inhibition of the binding of NBMPR to guinea pig, rabbit, and dog membranes (IC50 less than 20 nM and IC50 greater than 6 microM for NBMPR binding sites displaying high and low affinity for dipyridamole, respectively). These results are indicative of heterogeneity of NBMPR binding sites in mammalian cortical membranes. Rat and mouse cortical membranes appear to possess only one type of NBMPR binding site, which has low affinity for dipyridamole. Detailed analysis of inhibitor-induced dissociation of NBMPR from its sites in each species led to the conclusion that these multiple forms of NBMPR binding sites are different conformations of a single site associated with the CNS nucleoside transport system, rather than two distinct sites. It is also suggested that the affinity of dipyridamole for each conformation of NBMPR site indicates the susceptibility of that conformation of the nucleoside transport system to inhibition by dipyridamole.

[3H]nitrobenzylthioinosine binding to the guinea pig CNS nucleoside transport system: a pharmacological characterization

The binding of [3H]nitrobenzylthioinosine (NBMPR) to specific membrane sites in guinea pig brain was rapid, reversible, and saturable, and was dependent upon protein concentration, pH, and temperature. Mass law analysis of the binding data for cortical membranes indicated that NBMPR bound with high affinity to a single class of sites at which the equilibrium dissociation constant (KD) for NBMPR was 0.10-0.25 nM and which possessed a maximum binding capacity (Bmax) per mg of protein of 300 fmol of NBMPR. Kinetic analysis of the site-specific binding of NBMPR yielded an independent estimate of the KD of 0.16 nM. A relatively homogeneous subcellular distribution of the sites for NBMPR was found in cortical tissue. Recognized inhibitors of nucleoside transport were potent, competitive inhibitors of the binding of NBMPR in guinea pig CNS membranes whereas benzodiazepines and phenothiazines have low affinity for the sites. NBMPR sites in guinea pig cortical membranes have characteristics similar to those for NBMPR in human erythrocytes, the occupation of which is associated with inhibition of nucleoside transport. The comparable affinities for a range of agents for sites in human erythrocytes and guinea pig CNS membranes suggest that NBMPR also binds to transport inhibitory elements of the guinea pig CNS nucleoside transport system. It is proposed that the study of the binding of NBMPR provides an effective method by which to examine drug interactions with the membrane-located nucleoside transport system in CNS membranes.