Protective effect of atrial natriuretic peptide on electrical-field-stimulated rat ventricular strips during hypoxia

Atrial natriuretic factor in normothermic and hypothermic cardiopulmonary bypass

Background: To evaluate the plasmatic changes of atrial natriuretic factor (ANF) during and after cardiopulmonary bypass (CPB) in normothermia and hypothermia.

Methods: Twenty-three patients (n=23) undergoing coronary artery bypass graft surgery were randomly assigned to two groups. In Group I (n=11), the patients underwent operation in normothermia; in Group II (n=12), the operation was performed in hypothermia (268C).

Results: Plasma ANF levels were determined after induction of anaesthesia, at the end of CPB and one hour postoperatively. There were no demographic differences between the two groups, diuresis (p=0.90) and natriuresis (p=0.95). Plasma levels of ANF were significantly elevated during and after CPB in both groups (p <0.01). The groups differed significantly for plasma levels of ANF during CPB and postoperatively ( p<0.05), but did not differ prebypass (p=0.08). There was no correlation in either group between ANF release and central venous pressure, natriuresis and diuresis. There was only a borderline relationship between ANF concentration and diuresis after CPB in Group I.

Conclusion: CPB triggers the production and release of ANF. The present study demonstrates a significantly enhanced ANF release during hypothermia and reperfusion after ischaemia. Thus, these data suggest the protective role of ANF on the hypoxic myocardium, and they confirm that ANF does not play a role in diuresis and natriuresis during and after hypothermic CPB.

Phosphatidylinositol 3-kinase and ERK1/2 are not involved in adenosine A1, A2Aor A3receptor-mediated preconditioning in rat ventricle strips

Mitogen-activated protein kinase kinase (MEK)/extracellular signal-regulated kinase 1 and 2 (ERK1/2) and phosphatidylinositol 3-kinase (PI3-kinase)/protein kinase B (PKB; also known as Akt) are important antiapoptotic signalling pathways which have recently been implicated in cardioprotection. However, at present the involvement of ERK1/2 and PI3-kinase/PKB in adenosine receptor-mediated cardioprotection is poorly understood. In this study we used isolated rat right ventricular strips, contracted by electrical-field stimulation, in order to investigate the role of ERK1/2 and PI3-kinase/PKB in adenosine receptor-induced cardioprotection. Ventricle strips were pretreated for 2 min with the agonists adenosine (non-selective), CPA (A1 selective), CGS 21680 (A2A selective) and Cl-IB-MECA (A3 selective) before 30 min hypoxia followed by 30 min reoxygenation. Each agonist significantly improved posthypoxic percentage contraction recovery compared to control strips. Similarly hypoxic preconditioning (10 min hypoxia followed by 20 min reoxygenation) significantly improved posthypoxic percentage contraction recovery compared to non-preconditioned strips. The selective adenosine receptor antagonists DPCPX (A1), ZM 241385 (A2A) and MRS 1220 (A3) attenuated cardioprotection induced by CPA, CGS 21680 and Cl-IB-MECA, respectively. Pre-incubation (30 min) of ventricle strips with the MEK1 inhibitor PD 98059 (50 microM) or the PI3-kinase inhibitor wortmannin (100 nM) significantly reduced posthypoxic percentage contraction recovery induced by hypoxic preconditioning. In contrast, PD 98059 and wortmannin had no significant effect on cardioprotection induced by CPA, Cl-IB-MECA or CGS 21680. Overall these data indicate that although selective A1, A2A and A3 adenosine receptor agonists induce preconditioning in rat right ventricular strips the effects are independent of ERK1/2- and PI3-kinase-dependent pathways. In contrast ERK1/2 and PI3-kinase-dependent pathways do appear to be involved in early hypoxic preconditioning.

Atrial natriuretic peptide increases glucose uptake during hypoxia in cardiomyocytes

The action of atrial natriuretic peptide on glucose uptake during hypoxia was investigated in neonatal cardiomyocytes. When the cultures were exposed to 100 n and 1 and 10 micro M of atrial natriuretic peptide for 60 min, hypoxia-induced glucose uptake significantly increased from 20.4 +/- 1.2 to 28.2 +/- 3.1, 31.6 +/- 2.7, and 30.1 +/- 2.8 pmol/h/mg protein, respectively, although atrial natriuretic peptide alone did not significantly affect the basal glucose uptake in normoxic condition. The atrial natriuretic peptide-stimulated glucose uptake during hypoxia was significantly decreased by 100 n of genistein and tyrphostin A-23 (a tyrosine kinase inhibitor) from 31.6 +/- 2.7 to 22.8 +/- 2.4 and 23.8 +/- 2.7 pmol/h/mg protein. U73122 100 n, which is a phospholipase C antagonist, significantly inhibited the atrial natriuretic peptide-induced glucose uptake under hypoxic conditions from 31.6 +/- 2.7 to 13.6 +/- 1.9 pmol/h/mg protein. However, the atrial natriuretic peptide-induced glucose uptake did not involve elevation of intracellular Ca and phosphatidylinositol (PI)3 kinase. It was concluded that the atrial natriuretic peptide-stimulated glucose uptake during hypoxia acts through a phospholipase C-tyrosine kinase pathway.

Effects of intraoperative administration of atrial natriuretic peptide

BACKGROUND

Biological activity of endogenous atrial natriuretic peptide (ANP) may decrease during cardiopulmonary bypass. To evaluate the effects of intraoperative administration of exogenous ANP in patients undergoing cardiopulmonary bypass, we conducted a prospective randomized study.

METHODS

Eighteen patients undergoing mitral valve surgery were randomized to receive either ANP treatment (ANP group; n = 9) or no ANP treatment (control group; n = 9). Atrial natriuretic peptide was given immediately after initiation of cardiopulmonary bypass for 6 hours (0.05 microg x kg(-1) x min(-1)). Plasma ANP, brain natriuretic peptide and cyclic guanosine monophosphate (cGMP) levels, hemodynamic variables and renal function were assessed perioperatively.

RESULTS

Administration of ANP increased plasma cyclic guanosine monophosphate levels, urine output and fractional sodium excretion, and decreased preload, afterload and plasma brain natriuretic peptide levels significantly (p < 0.05). Plasma cyclic guanosine monophosphate levels correlated with plasma ANP levels (r = 0.95, p = 0.0001), correlated with fractional sodium excretion (r = 0.53, p = 0.02), and correlated inversely with systemic vascular resistance (r = -0.54, p = 0.02).

CONCLUSIONS

Intraoperative administration of ANP had potent effects on natriuresis and systemic vasodilation by elevating cyclic guanosine monophosphate levels. The results suggest that the technique is useful for the management of hemodynamics and water-sodium retention after cardiopulmonary bypass.

Myocardial circulatory and metabolic effects of atrial natriuretic peptide after coronary artery bypass grafting

The purpose of this study was to examine the effects of incremental infusion rates of human atrial natriuretic peptide (ANP), 25, 50, 100 ng.kg-1. min-1, on myocardial blood flow and metabolism (n = 10), and to compare the effects of ANP on these variables with those of equipotent infusion rates of sodium nitroprusside (SNP) (n = 9) 1-3 h after coronary artery bypass grafting (CABG). ANP induced a dose-dependent decrease in mean arterial blood pressure and systemic vascular resistance. There were no changes in cardiac index, heart rate, or cardiac filling pressures. ANP caused no changes in myocardial blood flow or its distribution, and caused no changes in myocardial oxygen extraction. Regional myocardial lactate uptake (RMLU) and extraction (RMLE) increased significantly (P < 0.05) at 50 ng.kg-1.min-1 (10.2 +/- 3.8 mumol/min and 8.2% +/- 3.0%, respectively) as compared to control (-1.1 +/- 3.0 mumol/min and -1.3% +/- 3.3%, respectively). RMLE and RMLU were significantly (P < 0.05) higher with ANP (5.7% +/- 2.5% and 6.8 +/- 3.7 mumol/min, respectively) compared to SNP (-1.5% +/- 2.1% and -0.1 +/- 3.7 mumol/min, respectively). We conclude that ANP has no dilatory effects on coronary vascular resistance vessels and thus lacks the potential to maldistribute flow, and that ANP improves myocardial lactate metabolism after CABG.