Grojec M S, Ishac E J, Kapocsi J, Kunos G
Laboratory of Physiologic and Pharmacologic Studies, National Institute on Alcohol Abuse and Alcoholism, Bethesda, Maryland 20892.
Arch Biochem Biophys. 1990 Nov 15;283(1):34-9. doi: 10.1016/0003-9861(90)90608-2.
The fatty acid composition of total lipids and the adrenoceptor-mediated activation of glycogenolysis were studied in isolated hepatocytes from rats maintained on a control diet or on an essential fatty acid (EFA)-free diet. In cells from rats on the EFA-free diet there was a marked reduction in linoleic and arachidonic acid (AA) contents and an increase in eicosatrienoic, oleic, and palmitoleic acid contents compared to controls. In freshly isolated cells from both groups, phosphorylase a activity was increased by phenylephrine or epinephrine but not by isoproterenol, and the effect of epinephrine was inhibited by phenoxybenzamine but not by propranolol. When control cells were preincubated in a serum-free buffer for 4 h before testing, the effect of phenylephrine on phosphorylase a activity was reduced, isoproterenol became a potent agonist and the effect of epinephrine was partially inhibited either by phenoxybenzamine or by propranolol. The emerging beta-adrenergic response in 4-h cells was associated with a marked potentiation of isoproterenol-induced cAMP accumulation. A similar 4-h preincubation of EFA-deficient cells resulted in a reduced response to phenylephrine while isoproterenol remained ineffective for increasing either phosphorylase a activity or cAMP production. The response of these 4-h cells to isoproterenol could be restored by in vivo replacement of the EFA-deficient diet with control diet for the last 4 weeks prior to the experiment, but not by the in vitro exposure of the EFA-deficient cells to 10 microM AA throughout the 4-h incubation period. Extending previous observations (Refs. (6-8)), the present results suggest that the time-dependent emergence of beta-adrenergic glycogenolysis, but not the parallel reduction of the alpha-adrenergic response, is mediated by AA or its metabolite(s), which probably act by facilitating the G-protein-dependent coupling of beta-receptors.
研究了给予对照饮食或无必需脂肪酸（EFA）饮食的大鼠分离肝细胞中总脂质的脂肪酸组成以及肾上腺素能受体介导的糖原分解激活情况。与对照组相比，无EFA饮食大鼠的细胞中，亚油酸和花生四烯酸（AA）含量显著降低，而二十碳三烯酸、油酸和棕榈油酸含量增加。在两组新鲜分离的细胞中，去氧肾上腺素或肾上腺素可增加磷酸化酶a活性，但异丙肾上腺素无此作用，且肾上腺素的作用可被酚苄明抑制，但不被普萘洛尔抑制。当对照细胞在无血清缓冲液中预孵育4小时后进行测试时，去氧肾上腺素对磷酸化酶a活性的作用减弱，异丙肾上腺素成为强效激动剂，肾上腺素的作用可被酚苄明或普萘洛尔部分抑制。4小时培养的细胞中出现的β-肾上腺素能反应与异丙肾上腺素诱导的cAMP积累显著增强有关。对EFA缺乏细胞进行类似的4小时预孵育，导致对去氧肾上腺素的反应减弱，而异丙肾上腺素对增加磷酸化酶a活性或cAMP生成均无效。在实验前的最后4周，用对照饮食对EFA缺乏饮食进行体内替代，可恢复这些4小时培养细胞对异丙肾上腺素的反应，但在整个4小时孵育期将EFA缺乏细胞体外暴露于10μM AA则不能恢复。扩展先前的观察结果（参考文献（6 - 8）），目前的结果表明，β-肾上腺素能糖原分解的时间依赖性出现，而非α-肾上腺素能反应的平行降低，是由AA或其代谢产物介导的，它们可能通过促进β受体的G蛋白依赖性偶联发挥作用。
