Biomedical subjects

J I Shapiro

Publications and source records attributed to J I Shapiro.

At least 19 recordsLinked to original sources

PubMed2001

Cardiac performance in inbred rat genetic models of low and high running capacity.

1. Previous work demonstrating that DA inbred rats are superior to COP inbred rats in aerobic treadmill running capacity has indicated their utility as genetic models to explore this trait. We tested the general hypothesis that intermediate phenotypes of cardiac function and calcium metabolism are responsible for the difference in capacity between these strains. 2. Logical cardiac trait differences were estimated at a tissue (isolated papillary muscle), cellular (isolated left ventricular cells), and biochemical level of organization. 3. DA hearts were found to give significantly higher values than COP hearts for: (1) maximal developed tension (38.3 % greater), and rates of tension change in contraction (61 %) or relaxation (59 %) of isolated papillary muscle, (2) fractional shortening (50 %), amplitude of the Ca(2+) transient (78.6 %), and caffeine-induced release of Ca(2+) from the sarcoplasmic reticulum (SR; 260 %) in isolated ventricular myocytes, and (3) Na(+),K(+)-ATPase activity of isolated myocytes (17.3 %). 4. Our results suggest that these trait differences may prove useful for further studies into the genes responsible for natural variations in both ventricular function and aerobic endurance capacity. Understanding the genetic basis of aerobic capacity will help define the continuum between health and disease.

Animals↗

PubMed2001

Effects of uremic serum on isolated cardiac myocyte calcium cycling and contractile function.

BACKGROUND: Diastolic dysfunction occurs in patients with chronic renal failure. Moreover, serum from uremic patients contains one or more inhibitors of the plasmalemmal Na,K-ATPase (sodium pump). We hypothesized that a circulating substance present in uremic sera contributes to both sodium pump inhibition and diastolic dysfunction. METHODS: Serum samples were obtained from six patients with chronic renal failure and diastolic dysfunction. RESULTS: Their serum samples caused marked inhibition of Na,K-ATPase purified from dog kidney at all concentrations studied (all P < 0.01) and also impaired ouabain-sensitive rubidium uptake by myocytes isolated from Sprague-Dawley rats (P < 0.01). These cardiac myocytes were studied for their contractile function with video-edge detection and calcium metabolism with indo-1 fluorescence spectroscopy after exposure to these uremic sera. These uremic sera caused increases in myocyte fractional shortening (P < 0.01) as well as an increase in the time constant of relengthening (P < 0.01). Examining the calcium transient, the time constant for calcium recovery was also increased (P < 0.01). Exposure of these cells to sera from age- and sex-matched healthy subjects did not result in significant changes in contraction or calcium cycling. Extracts of uremic serum samples inhibited isolated Na,K-ATPase whereas extracts of normal serum samples did not. The effect of uremic serum extracts on contractile function and calcium cycling were quite similar to that of intact serum or the addition of ouabain. Co-incubation of uremic serum extract with an antibody fragment directed against digoxin markedly attenuated the inhibition of Na,K-ATPase activity and completely prevented any effects on calcium cycling or contractile function. CONCLUSION: These data show that one or more substances are present in uremic sera that acutely cause increased force of contraction and impaired recovery of cardiac myocyte calcium concentration as well as impaired relaxation. As these effects are similar to that seen with ouabain and can be prevented by co-incubation with an antibody fragment to digitalis, which also attenuates the sodium pump inhibitory effect, we suggest that this (these) substance(s) circulating in uremic sera and inhibiting the sodium pump also causes the acute diastolic dysfunction seen in our system.

Adult↗

PubMed2001

Effects of enhanced oxygen release from hemoglobin by RSR13 in an acute renal failure model.

BACKGROUND: Acute renal failure is believed to be caused, in some circumstances, by impaired oxygen delivery to the outer medulla. This study examined the effect of RSR13, a synthetic allosteric modifier of hemoglobin oxygen-binding affinity, on renal function in a setting of acute renal failure in rats. METHODS: An in vivo model of acute renal failure in the rat produced by reduced renal mass, salt restriction, volume depletion, prostaglandin inhibition, and radiocontrast administration was used. A computer-based simulation of oxygen tensions along the nephron was utilized to interpret the findings. Mechanistic studies were subsequently performed using oxygen-sensitive electrodes and 31P nuclear magnetic resonance (NMR) spectroscopy to define the effect of RSR13 on renal function in the setting of compromised acute renal failure. RESULTS: RSR13 did not attenuate acute renal failure in this model; rather, serum creatinine increased to a greater degree in the RSR13-treated rats than in rats receiving saline vehicle as the control (P < 0.05). Simulations explained this finding under conditions of severe medullary hypoxia. Mechanistic studies demonstrated marked worsening of medullary hypoxia following RSR13 under conditions similar to our experimental model. Furosemide pretreatment to reduce the imbalance between oxygen supply and demand markedly attenuated the basal-medullary hypoxia produced in the presence of indomethacin and RSR13 (P < 0.01). Additionally, 31P NMR studies demonstrated renal adenosine 5'-triphosphate (ATP) depletion in rats with acute renal failure treated with RSR13 (45% decrease, P < 0.01); again, this effect of RSR13 was completely prevented by pretreatment with furosemide. CONCLUSIONS: Under conditions of severe renal medullary hypoxia, induced in part by indomethacin-mediated reductions in outer medullary blood flow, the administration of RSR13 can exacerbate acute renal dysfunction. However, reducing the rate of oxygen consumption by inhibiting sodium transport with furosemide pretreatment or post-treatment appears to be functionally protective.

Acute Kidney Injury↗

PubMed2001

A potential role for immune activation in hemodialysis hypotension.

The necessary exposure of blood to biomembranes during hemodialysis has been viewed by many as an immunogenic challenge leading to an acute phase response. In this study we examined the relationship between hemodialysis-induced immune activation and intradialytic hypotension, using the acute phase reactant serum C-reactive protein (CRP) as a surrogate for immunogenic activation. The maximum percent change in mean arterial pressure (MAP) was found to correlate significantly with CRP (r = 0.67, p < 0.05) in nine consecutive patients with a history of symptomatic hypotension during hemodialysis. In contrast, no correlation was found between CRP and maximum percent change in MAP in eight consecutive hemodialysis patients without intradialytic hypotension. Since interleukin-6 (IL-6) is a major regulator of CRP, the relationship between these two proteins was examined. Plasma IL-6 levels were found to correlate both with CRP (r = 0.67, p < 0.05) and with mean maximum percent change in MAP (r = 0.70, p < 0.05) in hemodialysis patients with a prior history of hypotension. IL-6 levels did not correlate with CRP or blood pressure in the hemodynamically stable patients. The results suggest that immune activation working through IL-6, CRP and other cytokines may play a role in the pathogenesis of hemodialysis hypotension in some patients.

Adult↗

PubMed2001

Initial evidence of endothelial cell apoptosis as a mechanism of systemic capillary leak syndrome.

BACKGROUND: Systemic capillary leak syndrome (SCLS) is a rare disorder of unknown etiology that is characterized by acute recurrent attacks of hypovolemic shock commonly following an inflammatory stimulus such as a viral illness. Prophylactic therapy is generally ineffective, and the outcome is frequently fatal. METHODS: In order to investigate the cellular mechanisms leading to SCLS, we examined the effects of sera from two patients with active SCLS on microvascular endothelial cell apoptosis in vitro. Apoptosis was determined by morphologic criteria, DNA fragmentation, annexin V stain, and by a quantitative photometric assay. The apoptotic pathway was investigated by Western blot of endothelial cells lysate after exposure to SCLS sera. RESULTS: The sera from patients with active SCLS mediated profound apoptosis of microvascular endothelial cells shortly after exposure. The exposed microvascular endothelial cells underwent immediate apoptosis as evidenced by morphologic changes, plasma membrane phosphatidylserine exposure, and by DNA fragmentation. Increased Bax/Bcl-2 ratio in endothelial cells exposed to SCLS sera was observed and suggested an oxidation injury as the possible mechanism for endothelial apoptosis. This potential mechanism was further explored by measuring intracellular reactive oxygen species (ROS) following SCLS serum exposure. Sera from both patients caused marked increases in ROS, initially detectable at 1 h and persisted for at least 12 h, with control serum from healthy subjects showing no effect on basal endothelial cell ROS concentrations. CONCLUSION: Components from the sera of patients with active systemic capillary leak syndrome in contrast to healthy subject sera mediate early and extensive endothelial apoptosis in vitro that is associated with oxidation injury. These data represent compelling initial evidence for oxidation-induced apoptosis as a likely mechanism for endothelial injury leading to SCLS.

Apoptosis↗

PubMed2000

Ouabain interaction with cardiac Na+/K+-ATPase initiates signal cascades independent of changes in intracellular Na+ and Ca2+ concentrations.

We have shown previously that partial inhibition of the cardiac myocyte Na(+)/K(+)-ATPase activates signal pathways that regulate myocyte growth and growth-related genes and that increases in intracellular Ca(2+) concentration ([Ca(2+)](i)) and reactive oxygen species (ROS) are two essential second messengers within these pathways. The aim of this work was to explore the relation between [Ca(2+)](i) and ROS. When myocytes were in a Ca(2+)-free medium, ouabain caused no change in [Ca(2+)](i), but it increased ROS as it did when the cells were in a Ca(2+)-containing medium. Ouabain-induced increase in ROS also occurred under conditions where there was little or no change in [Na(+)](i). Exposure of myocytes in Ca(2+)-free medium to monensin did not increase ROS. Increase in protein tyrosine phosphorylation, an early event induced by ouabain, was also independent of changes in [Ca(2+)](i) and [Na(+)](i). Ouabain-induced generation of ROS in myocytes was antagonized by genistein, a dominant negative Ras, and myxothiazol/diphenyleneiodonium, indicating a mitochondrial origin for the Ras-dependent ROS generation. These findings, along with our previous data, indicate that increases in [Ca(2+)](i) and ROS in cardiac myocytes are induced by two parallel pathways initiated at the plasma membrane: One being the ouabain-altered transient interactions of a fraction of the Na(+)/K(+)-ATPase with neighboring proteins (Src, growth factor receptors, adaptor proteins, and Ras) leading to ROS generation, and the other, inhibition of the transport function of another fraction of the Na(+)/K(+)-ATPase leading to rise in [Ca(2+)](i). Evidently, the gene regulatory effects of ouabain in cardiac myocytes require the downstream collaborations of ROS and [Ca(2+)](i).

Animals↗

PubMed2000

Effects of hypokalemia on cardiac growth.

In neonatal myocytes grown in culture, reductions in extracellular potassium concentration produced a hypertrophic response as assessed by induction of early response genes, atrial natriuretic peptide and skeletal actin, and repression of the alpha3 isoform of the sodium pump in a dose dependent manner. The degree of alpha3 repression appeared to be dose dependent with decreases in media (K). Similarly, decreases in media potassium concentrations caused increases in cytosolic calcium concentration in a dose dependent manner; moreover these increases in cytosolic calcium concentration correlated quite well with repression of alpha3 expression. In contrast, although moderate reductions of potassium concentration induced upregulation of skACT and ANP, severely reduced potassium concentrations caused repression of skACT and ANP expression. In parallel studies performed in vivo, 3-5 weeks dietary K restriction induced molecular phenotypical changes similar to that seen in the neonatal myocyte model without demonstrable growth as assessed by the heart weight/body weight ratio. However, when rates subjected to dietary K restriction were subsequently subjected to acute aortic constriction, cardiac growth was greater than in rats fed a control diet. These data suggest that hypokalemia may produce molecular phenotypic alterations consistent with cardiac hypertrophy as well as contribute to hypertrophy in an in vivo model.

Animals↗

PubMed1999

Intracellular reactive oxygen species mediate the linkage of Na+/K+-ATPase to hypertrophy and its marker genes in cardiac myocytes.

We showed before that in cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophy and transcriptional regulations of growth-related marker genes through multiple Ca2+-dependent signal pathways many of which involve Ras and p42/44 mitogen-activated protein kinases. The aim of this work was to explore the roles of intracellular reactive oxygen species (ROS) in these ouabain-initiated pathways. Ouabain caused a rapid generation of ROS within the myocytes that was prevented by preexposure of cells to N-acetylcysteine (NAC) or vitamin E. These antioxidants also blocked or attenuated the following actions of ouabain: inductions of the genes of skeletal alpha-actin and atrial natriuretic factor, repression of the gene of the alpha3-subunit of Na+/K+-ATPase, activation of mitogen-activated protein kinases, activation of Ras-dependent protein synthesis, and activation of transcription factor NF-kappaB. Induction of c-fos and activation of AP-1 by ouabain were not sensitive to NAC. Ouabain-induced inhibition of active Rb+ uptake through Na+/K+-ATPase and the resulting rise in intracellular Ca2+ were also not prevented by NAC. A phorbol ester that also causes myocyte hypertrophy did not increase ROS generation, and its effects on marker genes and protein synthesis were not affected by NAC. We conclude the following: (a) ROS are essential second messengers within some but not all signal pathways that are activated by the effect of ouabain on Na+/K+-ATPase; (b) the ROS-dependent pathways are involved in ouabain-induced hypertrophy; (c) increased ROS generation is not a common response of the myocyte to all hypertrophic stimuli; and (d) it may be possible to dissociate the positive inotropic effect of ouabain from its growth-related effects by alteration of the redox state of the cardiac myocyte.

Acetylcysteine↗

PubMed1999

Absence of a dose-response of cyclosporine levels to clinically used doses of diltiazem and verapamil.

We examined the effect of different doses of calcium channel blockers on plasma cyclosporine levels. As previously reported by multiple investigators, we observed that the administration of verapamil or diltiazem, but not nifedipine or isradipine, caused a significant increase in plasma cyclosporine levels achieved for a given dose of cyclosporine. In this article, we show that the effect of verapamil and diltiazem on cyclosporine levels appears to be independent of dosage within their usual prescription range.

Administration, Oral↗

PubMed1999

Time course of response to pulse methylprednisolone therapy in renal transplant recipients with acute allograft rejection.

All rejection episodes that occurred from 1990 to 1995 treated by the University of Colorado renal transplant service were evaluated through a review of patient charts. Seventy-one episodes of rejection were treated initially with pulse steroids consisting of pulse methylprednisolone, 500 mg/d for 3 days, with sufficient follow-up to determine whether the patient would respond to this treatment. There was no difference between responders and nonresponders to methylprednisolone treatment with respect to serum creatinine level at time of diagnosis, age of allograft, nadir serum creatinine level, or presence of oliguria. The time course of change in serum creatinine levels (in milligrams per deciliter) in responders and nonresponders was similar until day 5, at which time significant differences could be seen (P < 0.01). In the 34 patients treated with OKT3 (muromonab-CD3), statistically significant differences between responders and nonresponders were only seen at day 14, but the small number of nonresponders (n = 4) makes this analysis inconclusive. Based on these data, it appears one cannot truly evaluate whether a patient will respond to three daily pulses of methylprednisolone until at least 3 days have passed since completion of therapy.

Acute Disease↗

PubMed1999

Factors maintaining a pH gradient within the kidney: role of the vasculature architecture.

BACKGROUND: The architecture of the vasa rectae produces significant oxygen (O2) "shunting" and marked decreases in renal medullary pO2 values. We hypothesized that carbon dioxide (CO2) trapping and increases in medullary pCO2 along with decreases in medullary pH values should also accompany this O2 shunting. METHODS: We developed computer simulations employing a model of gas exchange through the countercurrent vasculature that predicted trapping of CO2 along with O2 shunting. To test the validity of this model directly, medullary pH was measured by using needle electrodes in the in situ kidney before and after the administration of mannitol or furosemide, or by decreasing blood flow with a transient decrease of renal perfusion pressure with a suprarenal clamp. Data are expressed as mean +/- SD. RESULTS: Medullary pH was lower than cortical pH (7.20 +/- 0.09 vs. 7.39 +/- 0.08, P < 0.01). Mannitol caused a decrease in medullary pH to 7.02 +/- 0.07 (P < 0.01), whereas furosemide increased medullary pH to 7. 31 +/- 0.09 (P < 0.01). Brief periods of severe hypotension decreased medullary pH to 6.90 +/- 0.09 (P < 0.01). CONCLUSIONS: These data demonstrate that a significant pH gradient exists within the kidney parenchyma. This gradient is related to the metabolic activity of the thick ascending limb of Henle and the countercurrent vascular architecture, and may be relevant to a variety of physiological phenomena involved in volume, electrolyte, and acid-based homeostasis.

Animals↗

PubMed1999

Ischemic preconditioning attenuates functional, metabolic, and morphologic injury from ischemic acute renal failure in the rat.

Ischemic preconditioning has been shown to ameliorate injury due to subsequent ischemia in several organs. However, relatively little is known about preconditioning and the kidney. To address this, rats were randomized to control (C, N = 14), 2 min of ischemic preconditioning (P2 N = 10), 3 periods of 2 min of ischemia separated by 5 min periods of reflow (P2,3 N = 7), or three 5 min periods of ischemia separated by 5 min of reflow (P5,3 N = 6) prior to 45 min of bilateral renal ischemia followed by 24 hours of reperfusion. We observed a lower serum creatinine after 24 hours of reflow in P2, P2, 3 but not P5, 3 rats compared with C. Histology was examined in the C and P2, 3 groups and demonstrated less severe injury in the P2, 3 group. To gain insight into the mechanism by which preconditioning ameliorated ischemic injury, we performed near IR spectroscopy and 31P NMR spectroscopy. Based on near IR spectroscopy, the P2, 3 group had closer coupling of cytochrome aa3 redox state with that of hemoglobin during reflow. In the 31P NMR studies, the changes in ATP and pHi were similar during ischemia, but the P2, 3 group recovered ATP and pHi faster than C. These data suggest that ischemic preconditioning may ameliorate ischemic renal injury as assessed by functional, metabolic and morphological methods. The mechanism(s) by which this occurs requires additional study.

Acute Kidney Injury↗

PubMed1998

Acute and chronic hypokalemia sensitize the isolated heart to hypoxic injury.

We examined the effects of acute and/or chronic hypokalemia on responses to 30 min of hypoxia and recovery in the isolated, perfused heart model. We found that both acute hypokalemia and chronic hypokalemia impaired contractility [expressed as maximum slope of pressure increase over time (dP/dt): 501 +/- 49 and 529 +/- 48 vs. 1,302 +/- 118 mmHg/s, P < 0.01] and recovery of ATP concentrations (determined with 31P NMR spectroscopy: 30 +/- 6 and 40 +/- 10 vs. 67 +/- 5% initial, P < 0.05) at 30 min of recovery. Moreover, the combination of acute hypokalemia and chronic hypokalemia had additive effects (dP/dt 166 +/- 15 mmHg/s and ATP 21 +/- 7% initial, both P < 0.01). We also measured cytosolic calcium with surface fluorescence spectroscopy after indo 1 loading. Acute hypokalemia and acute hypokalemia + chronic hypokalemia increased cytosolic calcium (averaged throughout the cardiac cycle) during and after hypoxia (390- to 460-nm ratio at 30 min of recovery: 0.46 +/- 0.07 and 0.65 +/- 0.07 vs. 0.18 +/- 0.03, P < 0.01), whereas control and chronic hypokalemia hearts had only small changes with hypoxia and recovery. Finally, when we examined mitochondria isolated from hearts perfused under experimental conditions, we found that chronic hypokalemia-alone mitochondria and chronic hypokalemia + acute hypokalemia mitochondria had marked impairment of state 3 respiration compared with control hearts (52 +/- 13 and 50 +/- 9 vs. 128 +/- 10 natm.min-1.mg protein-1 with succinate as substrate, P < 0.01), whereas acute hypokalemia mitochondria demonstrated only subtle changes. These data suggest that both acute hypokalemia and chronic hypokalemia impair cardiac responses to hypoxia. The mechanism may involve impairment of calcium metabolism, but cytosolic calcium alterations do not explain all of the metabolic and functional effects of acute hypokalemia and chronic hypokalemia in the setting of hypoxia.

Acute Disease↗

PubMed1998

Mechanisms of pH preservation during global ischemia in preconditioned rat heart: roles for PKC and NHE.

Ischemic preconditioning (PC) attenuates cardiac acidosis during global ischemia. This adaptation to ischemia is detectable before other better known indexes of PC are manifested. Clarification of the endogenous mechanisms may provide insights into how protein kinase C (PKC) signaling might be linked to altered intracellular biochemistry. 31P NMR studies of isolated, buffer-perfused rat heart were performed to determine whether functionally cardioprotective PC by cyclic ischemia (CI) and alpha1-adrenergic stimuli [phenylephrine (PE)] attenuated acidosis during ischemia and, if so, whether this 1) involves a PKC-dependent pathway and is due to 2) decreased glycolytic proton production, 3) an increase in proton buffering, or 4) proton extrusion. At the end of 20 min of global ischemia, both CI-PC (pH = 6.86 +/- 0.14) and PE-PC (pH = 6.90 +/- 0.13) attenuated end-ischemic acidosis (control pH = 6.54 +/- 0.1). PKC blockade with chelerythrine (Chel) prevented the attenuation of ischemic acidosis by PC stimuli (end-ischemic pH: CI + Chel, 6.43 +/- 0.06; PE + Chel, 6.17 +/- 0.17). End-ischemic lactate accumulation was decreased in CI-PC hearts (7.54 +/- 0.5 vs. control, 14.61 +/- 2.1 micromol/g wet wt) but not in those preconditioned through the alpha1-adrenergic receptor (12.25 +/- 0.9 micromol/g wet wt). Physiologically relevant buffers were not increased in the preconditioned groups. Blockade of the Na+/H+ exchanger [NHE; with 5-(N-ethyl-N-isopropyl) amiloride (EIPA) or HOE-694] eliminated the attenuation of ischemic acidosis seen with PC stimuli (pH: CI + EIPA, 6.5 +/- 0.1; PE + EIPA, 6.46 +/- 0.2; PE + HOE-694, 6.26 +/- 0.15; not significantly different from control). We conclude that CI and alpha1-adrenergic PC stimuli attenuate ischemic acidosis, and this may involve the cardiac amiloride-sensitive NHE. The signaling pathways of both these two stimuli appear to involve PKC.

Acidosis↗

PubMed1997

Effects of acetate on energy metabolism and function in the isolated perfused rat heart.

Impairment of cardiac contractile function is an important component of acetate associated hypotension during hemodialysis treatments. We examined the effect of acetate on cardiac energy metabolism using the isovolumic isolated perfused heart model. In this preparation, acetate (10 M) caused decreases in tissue ATP concentrations (12.3 +/- 0.8 vs. 15.6 +/- 1.0 micromol/g dry at 30 min, P < 0.05) as well as marked impairment of systolic function (dpdt = 863 +/- 135 vs. 1288 +/- 166 mm Hg/second at 30 min, P < 0.05). Although altering perfusate calcium concentrations (0.6, 1.2 and 2.4 mM) affected physiological responses to acetate (5 and 10 mM), the reductions in tissue ATP concentrations were similar. In isolated heart mitochondria, acetate (100 microM -10 mM) selectively impaired octanoate and palmityl carnitine supported State 3 respiration in a dose dependent fashion (P < 0.01), but did not affect respiration when succinate, pyruvate/malate or malate/glutamate was used as substrate. We suggest that high concentrations of acetate selectively impair fatty acid metabolism in heart issue. This in turn leads to decreases in ATP production and tissue ATP concentrations that ultimately result in impaired contractile function. As this occurs at relatively low concentrations of acetate, this finding may be relevant to other parenterally-administered acetate containing fluids.

Acetates↗

PubMed1997

Different preconditioning stimuli invoke disparate electromechanical and energetic responses to global ischemia in rat hearts.

One hypothesized mechanism of the cardioprotection provided by preconditioning is decreased utilization of ATP during ischemia. Although ATP levels in preconditioned heart during ischemia have been previously studied, contractile activity during ischemia has not been investigated. Contractile activity accounts for significant ATP consumption during ischemia. We hypothesized that preconditioning stimuli may conserve energy during the ischemic period by decreasing myocardial contractile energy expenditure prior to asystolic cardiac arrest. We studied three preconditioning stimuli: (i) four cycles of 5-min periods of ischemia (4 x 5' CI), (ii) 2 min of alpha 1-adrenergic stimulation (phenylephrine; PE), and (iii) 2 min of P1-purinergic stimulation (adenosine). The effects of these stimuli on myocardial ATP, ventricular contractility, and the time to cessation of electromechanical function (asystole) during the sustained ischemic period were then examined. Preconditioning stimuli (4 x 5' CI, phenylephrine, and adenosine) improved postischemic functional recovery compared with nonpreconditioned controls. Myocardial ATP contents at the end of 20 min of global ischemia were higher for adenosine-treated (9.0 +/- 1.5 mumol/g dry weight; p < 0.05) and PE-treated (9.9 +/- 1.9 mumol/g dryweight; p < 0.05) hearts than for controls (6.6 +/- 1.2 mumol/g dry weight). The CI hearts began with lower myocardial ATP levels (9.9 +/- 1.2 mumol/g dry weight; p < 0.05) than other groups prior to the sustained ischemic period (control 13.4 +/- 1.0 mumol/g dry weight). As a result of a lower rate of ATP depletion, ATP levels in the CI group were similar to the untreated control after 20 min of sustained ischemia (5.5 +/- 0.7 mumol/g dry weight). Preconditioning with 4 x 5' CI or adenosine (but not PE) led to earlier ventricular arrest. Only adenosine-treated hearts demonstrated a more rapid decline in ventricular contractility during sustained ischemia than did nonpreconditioned control hearts. We conclude that while the final recovery of ventricular contractility after asystolic arrest and reperfusion is improved by preconditioning with different stimuli (4 x 5' CI, adenosine, or PE), each stimulus conferred a characteristic electromechanical and energy conservation strategy during sustained ischemia. Adenosine conserved myocardial ATP content and reduced total cardiac work (developed pressure and heart beats). CI conserved myocardial ATP and minimized the number of ischemic cardiac beats. PE preserved myocardial ATP during ischemia without changing contractile behavior. Thus, energy conservation strategies during ischemia could contribute to the protection afforded by preconditioning stimuli, but the mechanisms appear to differ among stimuli.

Adenosine↗

PubMed1997

Pathogenesis of cardiac dysfunction during metabolic acidosis: therapeutic implications.

Based on work performed in many laboratories including our own, we suggest the following schematic shown in Figure 4 to explain metabolic acidosis and the effects of alkalinization therapy. Metabolic acidosis induces prompt and substantial decreases in cardiac functional performance. This is mediated by an intracellular acidosis which impairs cardiac function directly as well as leads to an impairment of cardiac energy metabolism which further impairs cardiac function. Attempts to alkalinize the cell with sodium bicarbonate therapy lead to a paradoxical intracellular acidosis and further impairment of cardiac function, whereas Carbicarb may correct the intracellular acidosis and improve physiological function. However, at the time which this paper was written, Carbicarb was not available for clinical use in the United States.

Acidosis↗

PubMed1996

Stress-induced cardioadaptation reveals a code linking hormone receptors and spatial redistribution of PKC isoforms.

Extracellular agents, including growth factors, cytokines and hormones, transmit their information into cells utilizing a balanced mosaic of intracellular phosphatases and kinases. How do these agonists select the correct substrates and modify them in order to produce defined physiological responses? Our studies have centered on the mechanisms of stress-induced cardioprotection (preconditioning) against postischemic dysfunction. In several species, the ischemia-reperfusion resistant phenotype appears to be induced by metabotropic-receptor pathways linked to PKC. Our results on the isolated rat heart show that each protective stimulus involves a characteristic mosaic of PKC isoforms, translocating into distinct cellular compartments. The distinct receptor-stimulated PKC isoform profile engaged by each extracellular metabotropic agent could allow the heart several overlapping modes of phenotypic adaptation to ischemia.

Animals↗