Iodinated radiographic contrast media possess antioxidant properties in vitro.

PURPOSE: To study potential properties of iodinated radiographic contrast media (IRCM) for intravascular use in in vitro free radical generating reactions. MATERIAL AND METHODS: Superoxide (*O2-) and hydroxyl (*OH) radicals were generated in xanthine oxidase and Fenton reactions. *O2- was assayed by the nitroblue tetrazolium (NBT) method, whereas *OH was assayed by an aromatic hydroxylation (2-hydroxybenzoic acid) method. Total antioxidant status (TAS) of test substances was determined by a colorimetric assay. Finally, acetyl-cholinesterase (AChE) activity was measured in the absence and presence of IRCM. RESULTS: High concentrations (>50 mM) of IRCM inhibited *O2- production, ionic more than non-ionic IRCM. Medium concentrations (25-50 mM) of IRCM reduced *OH production, and both types of IRCM were equally potent. Low concentrations (<25 mM) of non-ionic IRCM displayed higher antioxidant capacity than their ionic counterparts when tested in the TAS assay. Visipaque 320 (iodixanol) was found to have the highest TAS value, followed by Omnipaque 350 (iohexol), Hexabrix 320 (ioxaglate), and Urografin 370 (diatrizoate). CONCLUSION: IRCM have in vitro antioxidant properties in concentrations relevant for their clinical application. These properties may therefore be of potential importance when evaluating IRCM effects in vivo, particularly those concerning cardiovascular and renal function.

Identification and regulation of the gastric H+/K+-ATPase in the rat heart.

UNLABELLED: Previous reports indicate that H+/K+-adenosine triphosphatase (ATPase) might be expressed in the heart. AIMS: The objectives of the present study were to explore the presence of H+/K+-ATPase protein and gene expression in the rat heart and to investigate whether the enzyme could contribute to potassium transport across the sarcolemma. METHODS AND RESULTS: We performed reverse transcription-polymerase chain reaction (RT-PCR) on mRNA from myocardium and isolated cardiomyocytes using primers specific for the gastric H+/K+-ATPase alpha-subunit. The PCR products were sequenced and the predicted gastric H+/K+-ATPase sequence was verified. Western blots from myocardium detected a 34-kDa band and a 94-kDa band, indicating the beta-subunit and alpha-subunit of the gastric H+/K+-ATPase, respectively. Immunocytochemistry detected significant immunoreactivity of the beta-subunit in cardiomyocytes. H+/K+-ATPase-dependent potassium transport was assessed by 86Rb+-uptake in isolated cardiomyocytes. Both ouabain and the selective H+/K+-ATPase inhibitor Schering 28080 reduced 86Rb+-uptake at maximum specific inhibition, by 70 and 25%, respectively; the effects were additive. Competitive RT-PCR analysis indicated a significant upregulation of the myocardial H+/K+-ATPase in heart failure after myocardial infarction. CONCLUSION: The gastric isoform of H+/K+-ATPase is expressed in rat cardiac myocytes, both at transcript and protein levels. Functional studies indicate that the enzyme could contribute to potassium and pHi regulation in cardiomyocytes.

Cardioprotective effects of the MR contrast agent MnDPDP and its metabolite MnPLED upon reperfusion of the ischemic porcine myocardium.

PURPOSE: To evaluate whether manganese dipyridoxyl diphosphate (MnDPDP) or its metabolite manganese dipyridoxyl ethyldiamine (MnPLED) reduces post-ischemic myocardial injury. MATERIAL AND METHODS: Left anterior descending artery (LAD) in anesthetized pigs was occluded (30 min) followed by reperfusion (120 min) during hemodynamic monitoring and infarct assessment. Three micromol/kg MnDPDP, 1 micromol/kg MnPLED (or a mixture of both) or saline was injected i.v. 10 min before reperfusion followed by infusion of either 3 micromol/kg/h MnDPDP, 1 micromol/kg/h MnPLED (or a mixture of both) or saline. The plasma concentrations of MnDPDP, MnPLED and other metabolites (e.g., ZnDPDP and ZnPLED) were analyzed. RESULTS: Femoral blood flow was reduced by 60% during early reperfusion in controls, whereas only 23 and 31% reductions were seen in animals treated with MnDPDP and MnPLED. During that time, +LV/dP and -LV/dP (maximum rate of left ventricular isovolumic contraction and relaxation, respectively), systolic pressure and diastolic pressure fell significantly less in animals treated with MnDPDP or MnPLED. Three out of 5 control animals experienced ventricular fibrillation (VF) during reperfusion, whereas VF was not seen in any of the pigs treated with MnPLED or/and MnDPDP. The infarct sizes in saline- and MnPLED-treated animals were 39+/-6 and 16+/-5%, respectively, of the occluded areas. MnDPDP did not reduce the infarct size. A mixture of MnDPDP and MnPLED significantly reduced infarct size (10+/-4%). When reperfusion started and throughout reperfusion, almost all injected MnDPDP was present as Zn-metabolites. CONCLUSION: MnPLED seems to reduce reperfusion-induced cardiac dysfunction and infarct size in pigs. MnDPDP does not reduce infarct size in the pig, probably because of the rapid exchange of Mn2+ for Zn2+ taking place in the pig.

Hyperosmotic perfusion of the beating rat heart and the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger.

The aim of the present study was to investigate the role of the Na+/K+/2Cl- co-transporter and the Na+/H+ exchanger on contractile function and electrolyte regulation during hyperosmotic perfusion of the heart. Langendorff perfused rat hearts were subjected to hyperosmolal perfusion in 10-min intervals. Perfusates were made hyperosmotic by adding mannitol to the buffer (370, 450 and 600 mOsmol/kg H2O). Cardiac contractile function was monitored with a balloon in the left ventricle (LV) coupled to a pressure transducer. Cardiac effluent was sampled repeatedly throughout and after hyperosmotic perfusion and analysed for content of Na+, K+, and Cl-. All three hyperosmotic perfusates initially reduced LV developed pressure (LVDP), but for 370 and 450 mOsmol/kg H2O, LVDP recovered to baseline within 4 min of perfusion. With 600 mOsmol/kg H2O, LVDP recovered slowly and was 50% below baseline after 10 min of hyperosmotic perfusion. Inhibition of the Na+/H+ exchanger with 5-(N-ethyl-N-isopropyl) amiloride (EIPA) and 3-methylsulfonyl-4-piperidinobenzoyl-guanidine methanesulfonate (HOE 694) abolished the recovery of LVDP to the 600 mOsmol/kg H2O perfusate, whereas inhibition of the Na+/K+/2Cl- co-transporter had no impact on LVDP. Potassium was taken up by the heart during hyperosmotic perfusion and this uptake was significantly reduced with inhibition of the Na+/H+ exchanger. Intracellular pH was assessed with 31p magnetic resonance spectroscopy and hyperosmolality induced a significant alkalosis that was dependent upon the Na+/H+ exchanger. The rat heart responds to moderate elevations in osmolality with a transient reduction in contractile function, whereas an elevation of 300 mOsmol/kg H2O persistently reduces contractile function. The Na+/H+ exchanger, but not the Na+/K+/2Cl- co-transporter, is of importance in contractile recovery and electrolyte regulation during hyperosmotic perfusion in the rat heart.

Protective effects of repetitive injections of radiographic contrast media on the subsequent tolerance to ischemia in the isolated rat heart.

PURPOSE: Despite detailed knowledge of the effects of X-ray contrast media on cardiac function, no studies have examined the effect of contrast media injections on the subsequent tolerance to ischemia in the heart. METHODS: Isolated perfused rat hearts were exposed to repetitive injections of iohexol, iodixanol, or ioxaglate before 30 min of global ischemia and 120 min of reperfusion. These groups were compared with control (no pretreatment) and ischemic preconditioning known to reduce infarct size. Physiologic variables and infarct size were measured RESULTS: Pretreatment with iodixanol reduced infarct size significantly compared with control and thus afforded protection against ischemia. Injections with iohexol and ioxaglate reduced infarct size, although not significantly, compared with control. CONCLUSION: Pretreatment of the isolated rat heart with commonly used contrast media enhances the cardiac tolerance to subsequent ischemia. The mechanism behind this protective effect could not be determined, but could involve stretching of the heart and/or generation of nitric oxide.

Effect of magnesium infusion on bleeding time in healthy male volunteers.

Intravenous magnesium has proved to be valuable in the treatment of cardiac arrhythmias and eclampsia, but the specific mode of action is not established. In this study the effect of magnesium sulphate (MgSO4) infusion on bleeding time and endogenous prostacyclin (PGI2) production in healthy male volunteers was investigated. Thirty-five males (age 18-30 years) randomized in a double-blind, placebo-controlled, cross-over study were investigated. MgSO4 was given as a bolus (8 mmol, 12 min) followed by continuous infusion (8 mmol in 108 ml saline, 120 min). Control was equal volumes of physiological saline. Heart rate, blood pressure and bleeding time (according to Ivy) were recorded as well as blood concentrations of magnesium and creatinine. Urine PGI2 was analysed as the stable metabolite 6-keto-prostaglandin F1alpha (6-keto-PGF1alpha). Treatment with MgSO4 did not affect bleeding time (MgSO4; 8.4+/-3.5 vs. control 8.0+/-2.7 min) nor the production of PGI2 (MgSO4; 1.2 microg 6-keto-PGF1alpha/g creatinine vs. control; 1.1 microg 6-keto-PGF1alpha/g creatinine). Intravenous infusion of MgSO4 does not affect the PGI2/platelet axis in healthy male volunteers. Studies in patients with endothelium dysfunction and/or concomitant drug therapy are required before the anti-thrombogenic effect of MgSO4 in vivo is discarded.

Elevated levels of endogenous adenosine alter metabolism and enhance reduction in contractile function during low-flow ischemia: associated changes in expression of Ca(2+)-ATPase and phospholamban.

Adenosine has several potentially cardioprotective effects including vasodilatation, reduction in heart rate and alterations in metabolism. Adenosine inhibits catecholamine-induced increase in contractile function mainly through inhibition of phosphorylation of phospholamban (PLB), the main regulatory protein of Ca(2+)-ATPase in sarcoplasmic reticulum (SR), and during ischemia it reduces calcium (Ca2+) overload. In this study we examined the effects of endogenous adenosine on contractile function and metabolism during low-flow ischemia (LFI) and investigated whether endogenous adenosine can alter expression of the Ca(2+)-ATPase/PLB-system and other Ca(2+)-regulatory proteins. Isolated blood-perfused piglet hearts underwent 120 min 10% flow. Hearts were treated with either saline, the adenosine receptor blocker (8)-sulfophenyl theophylline (8SPT, 300 micromol/l) or the nucleoside transport inhibitor draflazine (1 micromol/l). During LFI, 8SPT did not substantially influence metabolic or functional responses. However, draflazine enhanced the reduction in heart rate, contractile force and MVO(2), with less release of H+ and CO2. Before LFI there were no significant differences between groups for any of the proteins (Ca(2+)-ATPase, ryanodine-receptor, Na+/K(+)-ATPase) or mRNAs (Ca(2+)-ATPase, PLB, calsequestrin, Na+/Ca(2+)-exchanger) measured. At end of LFI mRNA-level of PLB was higher in draflazine-treated hearts compared to both other groups (P<0.01 vs both). Also, at end of LFI protein-level of Ca(2+)-ATPase was lower in draflazine-treated hearts (P<0.05 vs both), and a parallel trend towards a lower mRNA-level was seen (P=0.11 vs saline and P=0.43 vs 8SPT). During LFI tissue Ca2+ tended to rise in saline- and 8SPT-treated hearts but not in draflazine-treated hearts (at end of LFI, P=0.01 vs 8SPT). We conclude that the amount of adenosine normally produced during LFI does not substantially influence function and metabolism. However, increased endogenous levels by draflazine enhance downregulation of function and reduce signs of anaerobic metabolism. At end of LFI associated changes in expression of PLB and Ca(2+)-ATPase were seen. The functional significance was not determined in the present study. However, altered protein-levels might influence Ca(2+)-handling in sarcoplasmic reticulum and thus affect contractile force and tolerance to ischemia.

Myocardial manganese elevation and proton relaxivity enhancement with manganese dipyridoxyl diphosphate. Ex vivo assessments in normally perfused and ischemic guinea pig hearts.

Manganese (Mn) dipyridoxyl diphosphate (MnDPDP) is the active component of a contrast medium for liver MRI. By being metabolized, MnDPDP releases Mn(2+), which is taken up and retained in hepatocytes. The study examined whether MnDPDP elevates Mn content and enhances proton relaxivity in normal myocardium, but not in ischemic myocardium with reduced coronary flow and impaired metabolism. Isolated guinea pig hearts were perfused at normal flow or low flow, inducing global subtotal ischemia. Ventricular ATP and Mn contents, T(1) and T(2) were measured. At normal flow tissue Mn content increased from the control level of 4.1 to 70.4 micromol/100g dry wt with MnDPDP (3000 microM), while low-flow perfusion with MnDPDP (3000 microM) resulted in a Mn content of 16.6 micromol/100 g dry wt. Prolonged ischemia (35 and 90 min) reduced tissue Mn down to the control level. T(1) shortening closely paralleled myocardial Mn elevations during both normal and low-flow perfusion. The use of a Mn(2+)-releasing contrast agent like MnDPDP may be a promising principle in MRI assessments of myocardial function and viability in coronary heart disease by revealing a differential pattern of changes in T(1) relative to coronary flow, cell Mn uptake and retention, ion channel function and metabolism.

Cardiac metal contents after infusions of manganese. An experimental evaluation in the isolated rat heart.

RATIONALE AND OBJECTIVES: Manganese dipyridoxyl diphosphate (MnDPDP), a contrast agent for liver MRI, releases free Mn2+ in a graded manner. The aim of the study was to compare the effects of brief versus prolonged infusions of MnDPDP and manganese chloride (MnCl2) on cardiac function, metabolism, Mn accumulation, and tissue metal content. METHODS: Isolated perfused rat hearts received 1-minute or 10-minute infusions of MnDPDP (100 microM, 1000 microM) or of MnCl2 (10 microM, 100 microM). Physiologic indices were measured intermittently, and tissue high-energy phosphate compounds and Ca/Fe/Mg/Mn/Zn contents were measured after a standardized Mn washout. RESULTS: One-minute and 10-minute infusions induced, respectively, minor and marked depressions of contractile function and corresponding elevations in myocardial Mn content. MnCl2 was markedly more potent than MnDPDP. Ten-minute infusions of the highest concentration of MnDPDP and MnCl2 lowered tissue Mg and elevated tissue Ca (MnCl2), whereas high-energy phosphates were unaffected. CONCLUSIONS: Mn uptake after Mn infusion is strongly related to the duration, concentration, and dose of free Mn ions. Differences in Mn accumulation between MnDPDP and MnCl2 were more pronounced after the 10-minute infusion.

Cardiac contractile function and electrolyte regulation during hyperosmolal stress: an experimental study in the isolated rabbit heart.

Perturbations of the extracellular osmotic environment leads to cell volume changes. The aim of the present study was to evaluate the effects of hyperosmolality on cardiac contractile function and in particular the role of ionic mechanisms anticipated to be operative during hyperosmolal exposure. Paced rabbit hearts were perfused in the Langendorff mode and were exposed to 330, 370, 410, 450 and 600 mOsm kg-1 in 10 min. intervals intervened by 15 min. isosmolal buffer perfusion (by adding mannitol). Thereafter, 370 and 600 mOsm kg-1 perfusates were chosen for investigation of the effects of inhibition of the Na-K-2Cl co-transporter (bumetanide 1 microM and 10 microM), the Na+/H+ exchanger (5-(N-ethyl-N-isopropyl amiloride (EIPA) 100 nM) and the Na+/K(+)-ATPase (ouabain 50 nM). After a rapid and transient decrease in left ventricular developed pressure, all perfusates up to 450 mOsm kg-1 increased LVDP. The 600 mOsm kg-1 perfusate initially reduced LVDP by 50%, but LVDP increased to 85% of initial value at the end of the 10 min. perfusion. EIPA attenuated the recovery of LVDP during perfusion with 600 mOsm kg-1, whereas bumetanide did not affect cardiac contractile function. A net uptake of potassium was observed during hyperosmolal perfusion. Inhibition of the Na+/H+ exchanger resulted in a continued release of cardiac water throughout hyperosmolal perfusion. Isolated perfused rabbit hearts tolerate considerable elevations in perfusate osmolality. Our results suggest that the Na+/H+ antiporter is activated on hyperosmolal exposure with a secondary activation of the Na+/K(+)-ATPase. Since inhibition with bumetanide did not affect contractility or electrolyte movements, the Na-K-2Cl co-transporter does not seem to play an important role in cardiac response to hyperosmolality in rabbits.

Manganese dipyridoxyl diphosphate: MRI contrast agent with antioxidative and cardioprotective properties?

Manganese dipyridoxyl diphosphate (MnDPDP) is a contrast agent for magnetic resonance imaging (MRI) of the liver. Aims of the study were to examine if MnDPDP possesses superoxide dismutase (SOD) mimetic activity in vitro, and if antioxidant protection can be demonstrated in an ex vivo rat heart model. Superoxide (*O-2) and hydroxyl radicals (*OH-) were generated in xanthine oxidase and Fenton reactions. Spin adducts with 5,5-dimethyl-1-pyrroline-N-oxide were detected by electron spin resonance spectroscopy. Contractile function and enzyme release were monitored in rat hearts during hypoxia-reoxygenation. Low microM concentrations of MnDPDP and its metabolite Mn dipyridoxyl ethylene-diamine (MnPLED) dismutated *O-2, but showed no activity in Fenton or catalase reactions. MnDPDP 30 microM improved contractile function and reduced enzyme release in rat hearts during reoxygenation. It is concluded that MnDPDP and MnPLED possess SOD mimetic activities and may thereby protect the heart in oxidative stress.

Hyperosmotic pretreatment reduces infarct size in the rat heart.

Preconditioning of the heart can be achieved by an ischemia/reperfusion stimulus, but also by stretching of the heart by an acute volume overload. Since manipulations of the extracellular osmolality affects cell size, we hypothesized that hyperosmotic pretreatment of the isolated perfused rat heart could reduce infarct size following regional ischemia (RI). Langendorff perfused rat hearts were subjected to 30 min RI by ligature of the main branch of the left coronary artery followed by 120 min reperfusion (control group). Ischemic preconditioning (IP-5') was achieved by 5 min total global ischemia and 5 min reperfusion prior to RI. Hyperosmotic pretreatment was accomplished by perfusion with a hyperosmotic buffer (600 mOsm/kg H2O by adding mannitol) for 1 min, 2 min or 5 min. At the end of the experiments, the hearts were cut into 2 mm slices, incubated with triphenyltetrazoliumchloride before scanning and computerized for estimation of infarct size. The average infarct size (as percentage of area at risk) in the control group was 42% and was significantly reduced to 16% by ischemic preconditioning and to 17% by 2 min hyperosmotic pretreatment. Neither 1 min nor 5 min hyperosmotic pretreatment reduced infarct size as compared to the controls. The infarct reducing effect of 2 min hyperosmotic pretreatment was not blunted by inhibition of protein kinase C (chelerytrine chloride), the Na+/H+-exchanger (HOE 694) or stretch-activated anion channels (gadolinium chloride). The results indicate that short-lasting hyperosmotic perturbations of the extracellular environment may precondition the heart to a subsequent ischemic insult.

Beta-adrenergic signalling and threshold adrenaline concentration for induction of fibrillation in the perfused heart pretreated with antihypertensive drugs.

Recent investigations have shown that antihypertensive drug treatment leads to enhanced myocardial beta-adrenoceptor sensitivity. This study was therefore conducted to establish whether or not such hypersensitivity might trigger myocardial arrhythmia subsequent to adrenaline exposure. Adult male Wistar rats (n = 6 per group) were treated with either placebo (vehicle), metoprolol (2.40 mg.kg-1.day-1), timolol (0.075 mg.kg-1.day-1), verapamil (5.50 mg.kg-1.day-1) or enalapril (0.50 mg.kg-1.day-1) for 20 consecutive days. Hearts were excised and perfused ad modum Langendorff in the presence of an adrenaline gradient (0-300 nM) for 20 min with either 3.0 mM or 5.9 mM of potassium in the perfusion buffer. Adrenaline threshold concentration (ATC, nanomolar) at myocardial fibrillation was recorded, as well as tissue cAMP contents, beta-adrenoceptor number, G-protein levels and signalling effector enzyme activities. The main findings were: (1) ATC and cAMP levels were affected in hearts perfused with low-concentration potassium buffer only. In terms of ATC, the beneficial effect of each drug regimen appeared to be in the rank order of: placebo = enalapril > verapamil > timolol > metoprolol. There was an inverse correlation between ATC and myocardial cAMP contents at the start of fibrillation; (2) Subsequent to fibrillation, beta-adrenoceptor number, hormone-elicited adenylate cyclase activities and Gs alpha:Gi2 alpha-ratio were no different from preperfusion values; (3) Significant inverse correlations between beta 1-adrenoceptor numbers and ATC were observed. We conclude that alterations in beta-adrenoceptor number, G proteins and cAMP induced by antihypertensive drugs are predictive of the myocardial sensitivity to adrenaline in terms of time to continuous and irrevocable fibrillation.

Importance of endogenous adenosine during ischemia and reperfusion in neonatal porcine hearts.

BACKGROUND: Adenosine has several potentially cardioprotective effects. We hypothesized that the effects of endogenous adenosine vary with degree of ischemia and that elevating endogenous levels is protective. METHODS AND RESULTS: Isolated blood-perfused piglet hearts underwent 120 minutes of low-flow ischemia (10% flow) or 90 minutes of zero-flow ischemia, all with 60 minutes of reperfusion. Hearts were treated with either saline, the adenosine receptor blocker 8-sulfophenyltheophylline (8SPT, 300 micromol x L(-1)), or the nucleoside transport inhibitor draflazine (1 micromol x L(-1)). In separate groups, biopsies were obtained before and at the end of ischemia. Compared with saline, 8SPT did not significantly alter functional recovery in either protocol. Draflazine significantly improved percent recovery of left ventricular systolic pressure both in the low-flow protocol (92+/-3% versus 75+/-2% [saline] and 73+/-3% [8SPT], P<.001 for both) and in the zero-flow protocol (76+/-3% versus 59+/-4% [saline] and 46+/-9% [8SPT], P<.05 for both). In the zero-flow protocol, draflazine also significantly reduced ischemic contracture and release of creatine kinase. Tissue adenosine at the end of ischemia was elevated by draflazine compared with saline-treated hearts: after low-flow ischemia to 0.10+/-0.05 versus 0.00+/-0.00 micromol x g(-1) dry wt (P<.05) and after zero-flow ischemia to 1.73+/-0.82 versus 0.15+/-0.03 micromol x g(-1) dry wt (P<.05). CONCLUSIONS: In neonatal porcine hearts, endogenous adenosine produced during ischemia does not influence ischemic injury or functional recovery. Elevating endogenous adenosine by draflazine elicits cardioprotection in both low-flow and zero-flow conditions.

Cardiovascular safety of MnDPDP and MnCl2.

PURPOSE: To investigate the apparent discrepancy between expected basic physiological responses at the cellular level and the in vivo behaviour of both MnDPDP and MnCl2 administered i.v. prompted parallel investigations of these substances. MATERIAL AND METHODS: Studies were performed in isolated perfused rat hearts, isolated bovine mesenteric arteries, conscious dogs, and dogs with acute ischaemic heart failure. RESULTS: These studies confirmed that Mn+2 at high concentrations acted as a calcium antagonist inducing negative inotropy. Mn+2 at low concentrations was an effective superoxide scavenger, conserving nitric oxide and facilitating vasodilation. Mn+2 maintained or elevated heart rate (HR) and blood pressure (BP), and did not worsen existing cardiac failure. MnDPDP was about 10 times less potent than MnCl2 in eliciting these cardiovascular responses. CONCLUSION: The ex vivo properties of Mn+2, inducing vasodilation and negative inotropy, are counter-balanced in vivo through the action of 2 mechanisms: extensive plasma protein binding reducing active M+2, and the release of catecholamines which maintain or even raise HR and BP. Taken together with pharmacokinetic factors, including maximal plasma concentrations in humans given the recommended 5 mumol/kg dose, it is concluded that MnDPDP in normal clinical use represents no safety risk to the cardiovascular system.

Postnatal changes in mechanisms mediating acetylcholine-induced relaxation in piglet femoral arteries.

We studied the nitric oxide-cGMP pathway in endothelium-dependent relaxation in femoral arterial rings from piglets at different postnatal ages. Responses to acetylcholine (ACh) and sodium nitroprusside (SNP) were examined in phenylephrine-precontracted rings from newborn (10-22-h) and 7 d (7-10-d)-old piglets. Relaxant responses were investigated in endothelium-denuded rings and endothelium-intact controls, and in endothelium-intact rings incubated with the nitric oxide synthase (NOS) inhibitor N(G)-monomethyl-L-arginine acetate (L-NMMA), indomethacin, or the superoxide anion generator 6-anilinoquinoline-5,8-quinone (LY83583). Arterial rings from both age groups relaxed to a similar degree in response to ACh. Relaxation in rings from newborn piglets was insensitive to NOS inhibition by L-NMMA, whereas in artery rings from 7-d-old piglets, the relaxant response was significantly inhibited by L-NMMA. Incubation with LY83583 gave an inhibition of ACh-induced relaxation very similar to that of L-NMMA. Incubation with indomethacin had no significant effect on ACh-induced relaxation in either age group. Artery rings from both age groups relaxed 100% to SNP; the 7-d-old group was more sensitive than the newborn. NOS inhibition potentiated SNP-induced relaxation in both groups, but the potentiating effect was of greater magnitude in the newborn. Our results indicate a difference in the mechanism(s) underlying ACh-induced relaxation in the femoral artery from newborn and 7-d-old piglets, with an intact relaxant response in rings from the newborn despite NOS inhibition. The SNP results indicate a down-regulated soluble guanylate cyclase in the newborn, possibly related to a difference in basal NO release between the two age groups.

Biophysical factors and contractile function during coronary bolus perfusion: an experimental study in the isolated guinea pig heart.

RATIONALE AND OBJECTIVES: The purpose of this study was to evaluate the role of biophysical factors (viscosity, temperature, osmalality, perfusion pressure, and ionic washout) on cardiac contractility during coronary bolus perfusions. METHODS: Guinea pig hearts were perfused in the osmolality mode at constant and high flow (30 mL/min) and were subjected to boluses (injected in 1-8 seconds) of purely nonionic media: mannitol and iohexol (in hyposmolal, isosmolal, and twice isosmolal forms) and iodixanol (in a hyposmolal form). RESULTS: All contrast media elicited a dose-dependent increase in aortic pressure and contractile variables that was attenuated by an increased osmolality. Elevation of aortic pressure was followed by an increase in left ventricular systolic pressure and, with iodixamol and iohexol, a subsequent elevation of left ventricular end-diastolic pressure. Moderate hypothermic solutions (29 degrees C) did not alter the responses. The ionic washout profile was the same for the three substances, as were the individual washout profiles for sodium, potassium, chloride, magnesium, and calcium. CONCLUSION: An increase in osmolality attenuates the increased contractility induced by a purely nonionic medium. A viscosity-induced rise in perfusion pressure may increase contractility. A moderate reduction in bolus temperature does not alter the contractile responses. The ionic washout profile is the same for the main cardioactive electrolytes.

Effects of MnDPDP, DPDP--, and MnCl2 on cardiac energy metabolism and manganese accumulation. An experimental study in the isolated perfused rat heart.

RATIONALE AND OBJECTIVES: Recent studies indicate that manganese dipyridoxyl diphosphate (MnDPDP) may function as a slow release agent for manganese ions (Mn++) and that MnDPDP is approximately 10 times less potent than manganese chloride (MnCl2) in depressing cardiac function. The authors examined the possibility that MnDPDP and MnCl2 may influence cardiac metabolism and enzyme release and lead to a tissue accumulation of Mn. METHODS: Manganese DPDP, DPDP--, or MnCl2 (1000 microM) was infused in isolated rat hearts, which were freeze-clamped at various time intervals during infusion (5 minutes) and recovery (14-minute washout). Enzyme (lactate dehydrogenase) release, tissue high energy phosphates, Mn contents, and physiologic indices were measured at various time intervals. RESULTS: No significant differences were noted for: lactate dehydrogenase in the treated groups; tissue creatine phosphate (CrP) and adenosine triphosphate in MnDPDP, DPDP--, and control groups; and tissue Mn in DPDP-- and control groups. Manganese-chloride and MnDPDP-treated hearts accumulated and retained Mn in an 8:1 ratio. Manganese chloride depressed cardiac function more effectively than MnDPDP. CONCLUSIONS: The study has shown that: heart tissue uptake and retention of Mn++ is rapid and effective; MnCl2 is approximately eight times more potent than MnDPDP in promoting these effects; and a rise in tissue Mn content to eight to nine times (MnDPDP) or 60 to 70 times (MnCl2) the normal level does not lead to acute side effects on cardiac energy metabolism, function, and enzyme release. The study indicates that MnDPDP may act like a slow release compound for Mn++ ions.

Manganese and the heart: acute cardiodepression and myocardial accumulation of manganese.

The aim of study was to assess acute effects of the divalent manganese ion (Mn2+) in an intact but isolated heart preparation. Rat hearts were perfused in the Langendorff mode at constant flow rate. Left ventricular (LV) developed pressure (LVDP). LV pressure first derivatives (LVdp/dt max and min), heart rate (HR) and aortic pressure (AoP) were recorded. Ventricular contents of high energy phosphate compounds (HEP) and Mn metal were measured at the end of experiment. Infusion of MnCl2 for 5 min with perfusate concentrations 1-3000 microM induced an immediate depression of contractile function at and above 30 microM and negative chronotropy at and above 300 microM. These IC50 values were found (microM): LVDP 250; LVdp/dt max 160; LVdp/dp min 120; HR 1000; and increase in AoP 80. Recovery of function during a 14 min washout period was rapid and extensive except for Mn2+ 3000 microM. Somewhat unexpected, Mr2+ 30-1000 microM raised coronary vascular resistance up to about twice the control level, whereas the vasoconstrictory response was overcome at 3000 microM. Mn2+ 3000 microM reduced tissue HEP Ventricular Mn content rose stepwise for perfusate Mn2+ above 1 microM up to about 55 times the control level for perfusate Mn2+ 3000 microM. It is concluded that: acute effects of Mn2+ like depression of contractility and rate is rapidly reversible; and rat hearts accumulate and buffer large amounts of Mn2+ without affecting cardiac function or energy metabolism in the acute stage.