de Mazancourt P, Lacasa D, Giot J, Giudicelli Y
Department of Biochemistry, Faculty of Medicine Paris-Quest, Centre Hospitalier de Poissy, France.
Endocrinology. 1989 Mar;124(3):1131-9. doi: 10.1210/endo-124-3-1131.
The aim of this study was to establish the mechanism by which adrenalectomy promotes the antilipolytic effect of the adenosine analog (-)-N6-(R-phenyl-isopropyl)adenosine (R-PIA) in rat fat cells. This action of adrenalectomy was not specific for R-PIA, since it was also observed with nicotinic acid and was prevented by phosphodiesterase inhibitors. In contrast, the inhibitory effect of R-PIA and nicotinic acid toward isoproterenol-stimulated cAMP accumulation was unaltered by adrenalectomy regardless of whether phosphodiesterase inhibitors were present. Whatever the conditions used, however, the cAMP levels in adrenalectomized rat adipocytes were one quarter to one third of those in sham-operated rats and remained below the limit over which variations in cAMP had no more influence in lipolysis. Both total and particulate low Km cAMP phosphodiesterase activities per adipocyte were decreased in adrenalectomized rats, but the stimulatory responses of the particulate enzyme to R-PIA remained unchanged. Pertussis toxin-catalyzed ADP ribosylation studies revealed a marked decrease in the total amount of the alpha-subunits of Go and the adenylate cyclase inhibitory regulatory protein Gi after adrenalectomy. However, the inhibitory dose-response curves of adenylate cyclase to R-PIA, nicotinic acid, GTP, guanylylimidodiphosphate, and guanosine 5'-O-(3-thiotriphosphate) were unaltered by adrenalectomy, indicating that the inhibitory function of Gi is unimpaired by adrenalectomy. Lastly, adrenalectomy resulted in a 60% reduction of the Mn2+-stimulated adenylate cyclase activity/adipocyte, which indicates that adrenalectomy causes a defect in adenylate cyclase catalytic activity. Thus, enhanced antilipolytic effects of R-PIA induced by adrenalectomy do not involve increased function of the adenosine receptor Gi-coupled adenylate cyclase inhibitory pathway, but are related to abnormally low intracellular cAMP levels due to defective adenylate cyclase catalytic activity.
本研究的目的是确定肾上腺切除术促进腺苷类似物（-）-N6-（R-苯基-异丙基）腺苷（R-PIA）对大鼠脂肪细胞抗脂解作用的机制。肾上腺切除术的这种作用并非R-PIA所特有，因为烟酸也有此作用，且磷酸二酯酶抑制剂可阻止该作用。相反，无论有无磷酸二酯酶抑制剂，肾上腺切除术均不改变R-PIA和烟酸对异丙肾上腺素刺激的环磷酸腺苷（cAMP）积累的抑制作用。然而，无论采用何种条件，肾上腺切除大鼠脂肪细胞中的cAMP水平仅为假手术大鼠的四分之一至三分之一，且仍低于cAMP变化对脂解作用不再产生影响的阈值。肾上腺切除大鼠的每个脂肪细胞中，总的和颗粒性低Km cAMP磷酸二酯酶活性均降低，但颗粒性酶对R-PIA的刺激反应保持不变。百日咳毒素催化的ADP核糖基化研究显示，肾上腺切除术后Go的α亚基总量以及腺苷酸环化酶抑制调节蛋白Gi显著减少。然而，肾上腺切除术并未改变腺苷酸环化酶对R-PIA、烟酸、鸟苷三磷酸（GTP）、鸟苷亚氨基二磷酸和鸟苷5'-O-（3-硫代三磷酸）的抑制剂量反应曲线，表明肾上腺切除术并未损害Gi的抑制功能。最后，肾上腺切除术导致每个脂肪细胞中锰离子刺激的腺苷酸环化酶活性降低60%，这表明肾上腺切除术导致腺苷酸环化酶催化活性存在缺陷。因此，肾上腺切除术诱导的R-PIA增强抗脂解作用并不涉及腺苷受体Gi偶联的腺苷酸环化酶抑制途径功能增强，而是与腺苷酸环化酶催化活性缺陷导致的细胞内cAMP水平异常降低有关。
