Nakazawa K, Kasuya Y, Shigenobu K
Department of Chemical Pharmacology, Faculty of Pharmaceutical Sciences, University of Tokyo, Japan.
Jpn J Pharmacol. 1987 Sep;45(1):89-95. doi: 10.1254/jjp.45.89.
Effects of phenylephrine on contraction and Ca-action potentials were investigated to clarify whether the alpha-adrenergic mechanism may play a role in chick ventricles. Phenylephrine increased the contractile force of the ventricles isolated from both embryonic and hatched chicks, while methoxamine did not affect their contractility. Developmental changes in the sensitivity to phenylephrine, i.e., increase with age from late embryonic to early neonatal stages, were quite similar to those to a beta-agonist, isoproterenol. The positive inotropism of phenylephrine was antagonized by phentolamine and sotalol, but not antagonized by prazosin or yohimbine. Isobutylmethylxanthine augmented the effect of phenylephrine. Maximum upstroke velocity of Ca-action potentials recorded in partially depolarized ventricles were enhanced by phenylephrine, and the enhancement was eliminated by sotalol but not by phentolamine. The results suggested that the beta-adrenergic action of phenylephrine may be involved in part of its positive inotropic effect, which is mediated by increased Ca-influx through sarcolemma. Another mechanism may also participate in the effects of phenylephrine, but may not necessarily be classified as an "alpha-adrenergic effect".
研究了去氧肾上腺素对收缩和钙动作电位的影响，以阐明α-肾上腺素能机制是否可能在鸡心室中发挥作用。去氧肾上腺素增加了从胚胎期和孵化后的雏鸡分离出的心室的收缩力，而甲氧明对其收缩性没有影响。对去氧肾上腺素敏感性的发育变化，即从胚胎后期到新生儿早期随年龄增加，与对β-激动剂异丙肾上腺素的变化非常相似。去氧肾上腺素的正性肌力作用被酚妥拉明和索他洛尔拮抗，但不被哌唑嗪或育亨宾拮抗。异丁基甲基黄嘌呤增强了去氧肾上腺素的作用。在部分去极化心室中记录的钙动作电位的最大上升速度被去氧肾上腺素增强，并且这种增强被索他洛尔消除，但不被酚妥拉明消除。结果表明，去氧肾上腺素的β-肾上腺素能作用可能参与了其部分正性肌力作用，这是由通过肌膜增加的钙内流介导的。另一种机制也可能参与去氧肾上腺素的作用，但不一定归类为“α-肾上腺素能效应”。
