Myocardial protection during cardiac surgery from the viewpoint of coronary endothelial function

L-arginine cardioplegia reduces oxidative stress and preserves diastolic function in patients with low ejection fraction undergoing coronary artery surgery

PL-arginine cardioplegia decreases biochemical markers of myocardial damage and oxidative stress in patients with normal left ventricular function. We investigated the effects of L-arginine supplemented cardioplegic arrest in patients with reduced ejection fraction. Fifty-three adult patients with left ventricular ejection fraction <35% undergoing elective coronary artery bypass surgery were randomised to receive blood cardioplegia with or without L-arginine. Following cardiopulmonary bypass, measured endpoints were cardiac troponin-I concentration at 12 and 24 hours, coronary sinus concentrations of malondialdehyde and superoxide dismutase activity at five and 15 minutes, lactic acid flux at one, five and 15 minutes and left ventricular systolic and diastolic function after protamine administration. There were no differences in cardiac troponin-I between groups. Malondialdehyde was lower in the L-arginine group, 0.28 ± 0.12 vs 0.48 ± 0.32 (5 minutes) and 0.31 ± 0.14 vs 0.38 ± 0.15 nmol.ml(-1) (15 minutes) (P=0.0004). Superoxide dismutase activity was higher in L-arginine group, 229 ± 87 vs 191.3 ± 68 (5 minutes), 229 ± 54 vs 198 ± 15 nmol.minute(-1).m(l) (15 minutes) (P=0.005). Lactic acid flux was lower in L-arginine group, 0.15 ± 0.23 vs 0.48 ± 0.32 (1 minute), 0.08 ± 0.19 vs 0.38 ± 0.31 (5 minutes) and -0.15 ± 0.13 vs 0.26 ± 0.30 mmol.l(-1) (15 minutes), (P=0.0003). There was no difference in left ventricular systolic function. The mitral annular tissue Doppler inflow (e') velocity during early diastole improved in the L-arginine group following cardiopulmonary bypass (control 4.2 ± 1.9 cm.s(-1) to 3.6 ± 1.2 cm.s(-1) vs L-arginine 3.8 ±1.2 cm.s(-1) to 4.6 ± 1.4 cm.s(-1)) (P=0.018). In patients with reduced ejection fraction, L-arginine supplemented cardioplegic arrest did not affect postoperative cardiac troponin-I levels, but attenuated cardiac cellular peroxidation and improved early left ventricular diastolic function.

Thiorphan enhances bradykinin-induced vascular relaxation in hypoxic/hyperkalaemic porcine coronary artery

Relaxation induced by bradykinin is diminished by hypoxia in epicardial coronary arteries. The bradykinin-degrading enzyme, neutral endopeptidase (NEP, EC.3.4.24.11), is a potential target for coronary artery vasodilators. In this study, we examined the effect of thiorphan, an inhibitor of NEP, on the tone of porcine isolated coronary artery under hypoxic conditions. Endothelium-intact porcine isolated coronary artery rings were isometrically contracted with a prostaglandin F(2alpha) analogue (U46619, 0.75 microM) and potassium chloride (KCl, 30 mM), and relaxed with bradykinin (1-1000 nM) under normoxic (partial pressure of oxygen, pO(2) approximately 90-100 mmHg) and moderately hypoxic (pO(2) approximately 50-60 mmHg) conditions. Experiments were performed to study the effects of 30 min pre-treatment with the NEP-inhibitor, thiorphan (10 microM), both at physiological and at low pO(2)s. Hypoxia inhibited the bradykinin-induced relaxation in porcine epicardial coronary arteries. In normoxia, thiorphan significantly enhanced the decrease of coronary tone produced by bradykinin (1-10 nM) when U46619 was used as contractile agent. Under hypoxic conditions, in U46619 contracture, thiorphan did not influence, but in KCl contracture it enhanced the magnitude of relaxations induced by bradykinin. In the absence of bradykinin, thiorphan had no significant effect on the basal, KCl- and U46619-elevated tones and on the hypoxia-induced decrease of coronary artery tone. Inhibition of NEP-enzyme activity may effectively improve the relaxing capacity of epicardial coronary arteries under hypoxic/hyperkalemic conditions. This effect could be potentially utilized when the endothelial function and relaxation of the coronary arteries are impaired under clinical conditions.

Nitric oxide and endothelium-derived hyperpolarizing factor in human arteries and veins

BACKGROUND

We have investigated and compared nitric oxide (NO) release and endothelium-derived hyperpolarizing factor (EDHF)-mediated hyperpolarization in the human internal mammary artery (IMA), radial artery (RA), saphenous vein (SV), and coronary artery.

MATERIALS AND METHODS

Vessel segments taken from coronary artery bypass grafting or heart transplantation patients were placed in an organ chamber. NO-sensitive electrode or intracellular glass microelectrode was used to study NO or EDHF in response to acetylcholine (ACh) and bradykinin (BK).

RESULTS

The resting membrane potential of the smooth muscle cells of IMA, RA, and SV was -58 +/- 0.84 (n = 61), -61 +/- 1.3 mV (n = 46, p = 0.03), and -62 +/- 0.9 mV (n = 23, p = 0.0001) respectively. BK- (10(-7) M) induced EDHF-mediated hyperpolarization (-10.9 +/- 1.5 mV, n = 7) in the IMA was significantly greater than that in RA (-5.8 +/- 0.9 mV, n = 6, p = 0.04) and SV (-5.1 +/- 0.5 mV, n = 8, p < 0.01). The basal release of NO in IMA (16.8 +/- 1.9 nM) was significantly higher than that in RA (11.1 +/- 1.0 nM, n = 12, p = 0.02) and in SV (9.9 +/- 2.8 nM, n = 13, p < 0.001). The stimulated release of NO to BK in IMA was significantly greater than that in RA (44.3 +/- 4.0 vs 25.8 +/- 3.6 nM, n = 8, p = 0.004). The duration of NO release was longer in IMA than in RA or in SV.

CONCLUSIONS

The basal and stimulated release of NO and EDHF-mediated hyperpolarization in the IMA are significantly greater than that in the RA and SV. EDHF exists in all these human vessels. This study reveals the differences among human vessels regarding the endothelial function that have implications in vasospasm, coronary protection, or long-term graft patency.