Gyurko R, Kuhlencordt P, Fishman M C, Huang P L
Cardiovascular Research Center and Cardiology Division, Department of Medicine, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts 02129, USA.
Am J Physiol Heart Circ Physiol. 2000 Mar;278(3):H971-81. doi: 10.1152/ajpheart.2000.278.3.H971.
To study the role of endothelial nitric oxide synthase (eNOS) in cardiac function, we compared eNOS expression, contractility, and relaxation in the left ventricles of wild-type and eNOS-deficient mice. eNOS immunostaining is localized to the macro- and microvascular endothelium throughout the myocardium in wild-type mice and is absent in eNOS-/- mice. Whereas blood pressure is elevated in eNOS-/- mice, baseline cardiac contractility (dP/dt(max)) is similar in wild-type and eNOS-/- mice (9,673 +/- 2, 447 and 9,928 +/- 1,566 mmHg/s, respectively). The beta-adrenergic agonist isoproterenol (Iso) at doses of >/=1 ng causes enhanced increases in dP/dt(max) in eNOS-/- mice compared with wild-type controls in vivo (P < 0.01) as well as in Langendorff isolated heart preparations (P < 0.02). beta-Adrenergic receptor binding (B(max)) is not significantly different in the two groups of animals (B(max) = 41.4 +/- 9.4 and 36.1 +/- 5.1 fmol/mg for wild-type and eNOS-/-). Iso-stimulated ventricular relaxation is also enhanced in the eNOS-/- mice, as measured by dP/dt(min) in the isolated heart. However, baseline ventricular relaxation is normal in eNOS-/- mice (tau = 5.2 +/- 1.0 and 5.6 +/- 1.5 ms for wild-type and eNOS-/-, respectively), whereas it is impaired in wild-type mice after NOS inhibition (tau = 8.3 +/- 2.4 ms). cGMP levels in the left ventricle are unaffected by eNOS gene deletion (wild-type: 3.1 +/- 0.8 pmol/mg, eNOS-/-: 3.1 +/- 0.6 pmol/mg), leading us to examine the level of another physiological regulator of cGMP. Atrial natriuretic peptide (ANP) expression is markedly upregulated in the eNOS-/- mice, and exogenous ANP restores ventricular relaxation in wild-type mice treated with NOS inhibitors. These results suggest that eNOS attenuates both inotropic and lusitropic responses to beta-adrenergic stimulation, and it also appears to regulate baseline ventricular relaxation in conjunction with ANP.
为研究内皮型一氧化氮合酶（eNOS）在心脏功能中的作用，我们比较了野生型和eNOS基因敲除小鼠左心室中eNOS的表达、收缩性及舒张功能。在野生型小鼠中，eNOS免疫染色定位于整个心肌的大、微血管内皮，而在eNOS基因敲除小鼠中则不存在。尽管eNOS基因敲除小鼠血压升高，但野生型和eNOS基因敲除小鼠的基线心脏收缩性（dP/dt(max)）相似（分别为9,673±2,447和9,928±1,566 mmHg/s）。在体内给予剂量≥1 ng的β-肾上腺素能激动剂异丙肾上腺素（Iso）后，与野生型对照相比，eNOS基因敲除小鼠的dP/dt(max)增加更为显著（P<0.01），在离体Langendorff心脏标本中也是如此（P<0.02）。两组动物的β-肾上腺素能受体结合（B(max)）无显著差异（野生型和eNOS基因敲除小鼠的B(max)分别为41.4±9.4和36.1±5.1 fmol/mg）。通过离体心脏中的dP/dt(min)测量发现，Iso刺激的心室舒张在eNOS基因敲除小鼠中也增强。然而，eNOS基因敲除小鼠的基线心室舒张功能正常（野生型和eNOS基因敲除小鼠的τ分别为5.2±1.0和5.6±1.5 ms），而野生型小鼠在抑制NOS后心室舒张功能受损（τ=8.3±2.4 ms）。左心室中的cGMP水平不受eNOS基因缺失的影响（野生型：3.1±0.8 pmol/mg，eNOS基因敲除小鼠：3.1±0.6 pmol/mg），这促使我们检测cGMP的另一种生理调节因子的水平。心房利钠肽（ANP）的表达在eNOS基因敲除小鼠中显著上调，外源性ANP可恢复用NOS抑制剂处理的野生型小鼠的心室舒张功能。这些结果表明，eNOS减弱了对β-肾上腺素能刺激的变力性和变时性反应，并且似乎还与ANP共同调节基线心室舒张功能。
