Hutson N J, Brumley F T, Assimacopoulos F D, Harper S C, Exton J H
J Biol Chem. 1976 Sep 10;251(17):5200-8.
Epinephrine and the alpha-adrenergic agonist phenylephrine activated phosphorylase, glycogenolysis, and gluconeogenesis from lactate in a dose-dependent manner in isolated rat liver parenchymal cells. The half-maximally active dose of epinephrine was 10-7 M and of phenylephrine was 10(-6) M. These effects were blocked by alpha-adrenergic antagonists including phenoxybenzamine, but were largely unaffected by beta-adrenergic antagonists including propranolol. Epinephrine caused a transient 2-fold elevation of adenosine 3':5'-monophosphate (cAMP) which was abolished by propranolol and other beta blockers, but was unaffected by phenoxybenzamine and other alpha blockers. Phenoxybenzamine and propranolol were shown to be specific for their respective adrenergic receptors and to not affect the actions of glucagon or exogenous cAMP. Neither epinephrine (10-7 M), phenylephrine (10-5 M), nor glucagon (10-7 M) inactivated glycogen synthase in liver cells from fed rats. When the glycogen synthase activity ratio (-glucose 6-phosphate/+ glucose 6-phosphate) was increased from 0.09 to 0.66 by preincubation of such cells with 40 mM glucose, these agents substantially inactivated the enzyme. Incubation of hepatocytes from fed rats resulted in glycogen depletion which was correlated with an increase in the glycogen synthase activity ratio and a decrease in phosphorylase alpha activity. In hepatocytes from fasted animals, the glycogen synthase activity ratio was 0.32 +/- 0.03, and epinephrine, glucagon, and phenylephrine were able to lower this significantly. The effects of epinephrine and phenylephrine on the enzyme were blocked by phenoxybenzamine, but were largely unaffected by propranolol. Maximal phosphorylase activation in hepatocytes from fasted rats incubated with 10(-5) M phenylephrine preceded the maximal inactivation of glycogen synthase. Addition of glucose rapidly reduced, in a dose-dependent manner, both basal and phenylephrine-elevated phosphorylase alpha activity in hepatocytes prepared from fasted rats. Glucose also increased the glycogen synthase activity ratio, but this effect lagged behind the change in phosphorylase. Phenylephrine (10-5 M) and glucagon (5 x 10(-10) M) decreased by one-half the fall in phosphoryalse alpha activity seen with 10 mM glucose and markedly suppressed the elevation of glycogen synthase activity. The following conclusions are drawn from these findings. (a) The effects of epinephrine and phenylephrine on carbohydrate metabolism in rat liver parenchymal cells are mediated predominantly by alpha-adrenergic receptors. (b) Stimulation of these receptors by epinephrine or phenylephrine results in activation of phosphorylase and gluconeogenesis and inactivation of glycogen synthase by mechanisms not involving an increase in cellular cAMP. (c) Activation of beta-adrenergic receptors by epinephrine leads to the accumulation of cAMP, but this is associated with minimal activation of phosphorylase or inactivation of glycogen synthase...
在分离的大鼠肝实质细胞中，肾上腺素和α-肾上腺素能激动剂去氧肾上腺素以剂量依赖性方式激活磷酸化酶、糖原分解以及由乳酸生成葡萄糖的糖异生作用。肾上腺素的半数最大活性剂量为10⁻⁷M，去氧肾上腺素的半数最大活性剂量为10⁻⁶M。这些作用被包括酚苄明在内的α-肾上腺素能拮抗剂阻断，但很大程度上不受包括普萘洛尔在内的β-肾上腺素能拮抗剂的影响。肾上腺素使腺苷3':5'-单磷酸（cAMP）瞬时升高2倍，这一升高被普萘洛尔和其他β受体阻滞剂消除，但不受酚苄明和其他α受体阻滞剂的影响。已证明酚苄明和普萘洛尔对各自的肾上腺素能受体具有特异性，且不影响胰高血糖素或外源性cAMP的作用。在喂食大鼠的肝细胞中，肾上腺素（10⁻⁷M）、去氧肾上腺素（10⁻⁵M）和胰高血糖素（10⁻⁷M）均未使糖原合酶失活。当通过用40mM葡萄糖预孵育此类细胞使糖原合酶活性比（-葡萄糖6-磷酸/+葡萄糖6-磷酸）从0.09增加到0.66时，这些药物可使该酶大量失活。对喂食大鼠的肝细胞进行孵育导致糖原耗竭，这与糖原合酶活性比增加和磷酸化酶α活性降低相关。在禁食动物的肝细胞中，糖原合酶活性比为0.32±0.03，肾上腺素、胰高血糖素和去氧肾上腺素能够使其显著降低。肾上腺素和去氧肾上腺素对该酶的作用被酚苄明阻断，但很大程度上不受普萘洛尔的影响。在用10⁻⁵M去氧肾上腺素孵育的禁食大鼠肝细胞中，磷酸化酶的最大激活先于糖原合酶的最大失活。添加葡萄糖以剂量依赖性方式迅速降低了禁食大鼠制备的肝细胞中基础和去氧肾上腺素升高的磷酸化酶α活性。葡萄糖还增加了糖原合酶活性比，但这种作用落后于磷酸化酶的变化。去氧肾上腺素（10⁻⁵M）和胰高血糖素（5×10⁻¹⁰M）使10mM葡萄糖引起的磷酸化酶α活性下降减半，并显著抑制糖原合酶活性的升高。从这些发现中得出以下结论。（a）肾上腺素和去氧肾上腺素对大鼠肝实质细胞碳水化合物代谢的作用主要由α-肾上腺素能受体介导。（b）肾上腺素或去氧肾上腺素对这些受体的刺激通过不涉及细胞cAMP增加的机制导致磷酸化酶激活和糖异生以及糖原合酶失活。（c）肾上腺素对β-肾上腺素能受体的激活导致cAMP积累，但这与磷酸化酶的最小激活或糖原合酶的失活相关……
