Hypothermia and cardiac contractile function in the isolated rat heart

Introduction: Metabolic suppression in the ischemic heart is characterized by NAD + depletion. How nicotinamide (NAM) supplementation affects NAD + repletion and cardiac arrest outcomes is unknown. Hypothesis: We hypothesized that NAM supplementation restores tissue NAD + and promotes glucose oxidation and sorbitol clearance, resulting in improved cardiac function and survival in a mouse model of cardiac arrest. Methods: Adult C57BL6 mice were subjected to an established KCL-induced 8 min cardiac arrest, randomly assigned to receive saline (NS) or 100 mg/kg NAM during cardiopulmonary resuscitation (CPR). Survival, MAP, ETCO 2, and ECG were monitored for 4 h after the return of spontaneous circulation (ROSC). Direct cardiac effects were assessed using a cardiomyocyte stunning model and an isolated rat heart Langendroff model to measure the contraction recovery and cardiac function, respectively. NAD + , lactate and ATP were measured by assay kits and AMPK phosphorylation was measured by Western blot. Results: Cardiomyocyte NAD + content decreased from 4.51 ± 0.03 nMol/g pre-ischemia to 2.69 ± 0.42 nMol/g at the end of ischemia. Treatment with 0.01 mM NAM completely restored the cellular level of NAD + and improved contractile recovery by 10 min reperfusion (58.1 ± 7.3% of baseline contractile velocity vs.18.5 ± 3.7% in control cells). NAM administered immediately after ROSC significantly improved mouse survival, with 10/10 survival at 4 h as compared to 5/10 in the NS group. NAM-treated mice displayed improved NAD + content in hearts obtained at 4 h post-ROSC compared to saline treated hearts (4.5 ± 0.1 nMol/g vs. 2.4 ± 0.1 nMol/g). NAM significantly reduced sorbitol accumulation in heart from saline control of 20.4 ± 2.7 μMol/g to 7.2 ± 1.5 μMol/g at 30 min post-ROSC, indicating less glucose shunting to polyol pathway. Cardiac contractile function was completely recovered with 1 mM NAM treatment in the isolated perfused rat heart. Compared with buffer control, NAM treatment increased heart content of NAD + , lactate, ATP and phosphorylated AMPK. Conclusion: NAM is efficacious for restoring cardiac NAD + and promotes metabolic and contractile recovery, with improved survival of cardiac arrest.

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Effect of Chronic Continuous Normobaric Hypoxia on Functional State of Cardiac Mitochondria and Tolerance of Isolated Rat Heart to Ischemia and Reperfusion: Role of µ and δ2 Opioid Receptors

Physiological Research ◽

10.33549/physiolres.933945 ◽

2019 ◽

pp. 909-920 ◽

Cited By ~ 1

Author(s):

E.S. Prokudina ◽

N.V. Naryzhnaya ◽

A.V. Mukhomedzyanov ◽

A.S. Gorbunov ◽

Y. Zhang ◽

...

Keyword(s):

Creatine Kinase ◽

Opioid Receptors ◽

Mitochondrial Function ◽

Rat Heart ◽

Contractile Function ◽

Isolated Rat Heart ◽

Retention Capacity ◽

Calcium Retention ◽

Calcium Retention Capacity ◽

Isolated Rat

Chronic continuous normobaric hypoxia (CNH) increases cardiac tolerance to ischemia/reperfusion injury in vivo and this effect is mediated via µ and δ2 opioid receptors (ORs) activation. CNH has also been shown to be cardioprotective in isolated rat heart. In this study, we hypothesize that this cardioprotective effect of CNH is mediated by activation of µ and δ2 ORs and preservation of mitochondrial function. Hearts from rats adapted to CNH (12 % oxygen) for 3 weeks were extracted, perfused in the Langendorff mode and subjected to 45 min of global ischemia and 30 min of reperfusion. Intervention groups were pretreated for 10 min with antagonists for different OR types: naloxone (300 nmol/l), the selective δ OR antagonist TIPP(ψ) (30 nmol/l), the selective δ1 OR antagonist BNTX (1 nmol/l), the selective δ2 OR antagonist naltriben (1 nmol/l), the selective peptide μ OR antagonist CTAP (100 nmol/l) and the selective κ OR antagonist nor-binaltorphimine (3 nmol/l). Creatine kinase activity in coronary effluent and cardiac contractile function were monitored to assess cardiac injury and functional impairment. Additionally, cardiac tissue was collected to measure ATP and to isolate mitochondria to measure respiration rate and calcium retention capacity. Adaptation to CNH decreased myocardial creatine kinase release during reperfusion and improved the postischemic recovery of contractile function. Additionally, CNH improved mitochondrial state 3 and uncoupled respiration rates, ADP/O, mitochondrial transmembrane potential and calcium retention capacity and myocardial ATP level during reperfusion compared to the normoxic group. These protective effects were completely abolished by naloxone, TIPP(ψ), naltriben, CTAP but not BNTX or nor-binaltorphimine. These results suggest that cardioprotection associated with adaptation to CNH is mediated by µ and δ2 opioid receptors activation and preservation of mitochondrial function.

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