Silver P J, Harris A L, Canniff P C, Lepore R E, Bentley R G, Hamel L T, Evans D B
Department of Pharmacology, Sterling-Winthrop Research Institute, Rensselaer, New York 12144.
J Cardiovasc Pharmacol. 1989 Apr;13(4):530-40.
The purpose of the present study was to examine the interrelationships among phosphodiesterase (PDE) isozyme inhibition, cAMP formation, activation of cAMP-dependent protein kinase (cAPK), and positive inotropy in isolated guinea pig cardiac muscle mediated by the cardiotonic/vasodilator agent, milrinone. Milrinone was a potent and selective inhibitor of the "low Km" cAMP PDE isozyme (peak III) isolated by diethylaminoethyl ether cellulose chromatography, with IC50 values of 0.7 microM for peak III PDE and 100 microM for peak I PDE. In isolated papillary muscles frozen at peak inotropic responses, positive and significant correlations were evident between isometric force development as a function of cAMP content (r = 0.72, p less than 0.05) or cAPK activity ratio, an index of activation of cAPK (r = 0.79, p less than 0.001), for concentrations of milrinone from 0.1-1000 microM. Similar correlations were evident in muscles frozen at peak inotropic responses for the beta-adrenoreceptor agonist isoproterenol (r = 0.96, p less than 0.001; r = 0.98, p less than 0.001, respectively), but not for ouabain or Bay K-8644. The temporal sequence of these events was also quantitated for concentrations of milrinone (100 microM) and isoproterenol (3 nM) that produced approximately a 100% increase in isometric force. Whereas early time interval of force development (30 s, 1 min, isoproterenol; 30 s milrinone) were not accompanied by significant increases in either cAMP content or cAPK activity ratio, peak increases in force development for both isoproterenol (2 min) and milrinone (1 min) were related to peak increases in cAPK activity ratios. In summary, these results show that significant increases in cAMP content or cAPK activation are correlated with positive inotropy in isolated guinea pig papillary muscles with milrinone. These correlations occur at concentrations of milrinone that inhibit cardiac PDE isozymes and are similar to the known cAMP-dependent cardiostimulant isoproterenol. These data support the hypothesis that selective PDE isozyme inhibition is a mechanism by which milrinone effects positive inotropy.
本研究的目的是探讨强心/血管扩张剂米力农介导的豚鼠离体心肌中磷酸二酯酶（PDE）同工酶抑制、环磷酸腺苷（cAMP）生成、环磷酸腺苷依赖性蛋白激酶（cAPK）激活与正性肌力作用之间的相互关系。米力农是通过二乙氨基乙基纤维素色谱法分离得到的“低Km”cAMP PDE同工酶（峰III）的强效选择性抑制剂，峰III PDE的IC50值为0.7 microM，峰I PDE的IC50值为100 microM。在以最大正性肌力反应时冻结的离体乳头肌中，对于0.1 - 1000 microM浓度的米力农，等长力的产生与cAMP含量（r = 0.72，p < 0.05）或cAPK活性比（cAPK激活的指标，r = 0.79，p < 0.001）呈正相关且具有显著性。在以最大正性肌力反应时冻结的肌肉中，β - 肾上腺素能受体激动剂异丙肾上腺素也有类似的相关性（分别为r = 0.96，p < 0.001；r = 0.98，p < 0.001），但哇巴因或Bay K - 8644则没有。对于使等长力增加约100%的米力农（100 microM）和异丙肾上腺素（3 nM）浓度，还对这些事件的时间顺序进行了定量分析。虽然早期的力发展时间段（30秒、1分钟，异丙肾上腺素；30秒，米力农）并没有伴随着cAMP含量或cAPK活性比的显著增加，但异丙肾上腺素（2分钟）和米力农（1分钟）的力发展峰值增加与cAPK活性比的峰值增加相关。总之，这些结果表明，米力农作用下豚鼠离体乳头肌中cAMP含量或cAPK激活的显著增加与正性肌力作用相关。这些相关性出现在抑制心脏PDE同工酶的米力农浓度下，并且与已知依赖cAMP的心脏兴奋剂异丙肾上腺素相似。这些数据支持了选择性PDE同工酶抑制是米力农产生正性肌力作用的一种机制这一假说。
