Conway J G, Neptun D A, Garvey L K, Popp J A
Carcinogenesis. 1987 Jul;8(7):999-1004. doi: 10.1093/carcin/8.7.999.
The effect of carcinogen treatment on gamma-glutamyl transpeptidase (GGT)-mediated hydrolysis of GSH to glutamate and cysteinylglycine in the blood and bile compartments was investigated in livers perfused in situ. Treatment of rats with 40 p.p.m. diethylnitrosamine (DEN) in the drinking water or 0.02% 2-acetylaminofluorene (AAF) in the diet for 50-60 days increased GGT activity in liver homogenates by 100 and 800% respectively. Bile flow and the sum of glutamate and glutathione (GSH) efflux into the bile of perfused livers was not affected by carcinogen treatment. However, the ratio of GSH to glutamate in bile was 2.1, 1.1 and 0.2 in livers from control, DEN- and AAF-treated rats respectively. Pretreatment with L-(alpha S,5S)-alpha-amino-3-chloro-4,5-dihydro-5-isoxazoleacetic acid (AT125) decreased GGT activity in liver homogenates by about 85% and elevated the ratio of GSH to glutamate in the bile to 3.2 in all groups. Thus, the hydrolysis of GSH to glutamate in the bile of perfused livers correlated with the degree of induction of GGT by DEN and AAF treatments. Exogenous GSH (10 microM) infused into the portal vein of perfused livers from control, DEN- and AAF-treated rats was recovered completely in the effluent perfusate. Pretreatment with AT125 had no effect on the recovery of exogenous GSH in the effluent perfusate. Thus, metabolism of GSH in the blood space was not detected after short-term carcinogen treatment. To increase the possible hydrolysis of GSH in the perfusate, rats were treated for 130-180 days with DEN and GSH (60 microM) was infused into the hepatic artery of livers perfused simultaneously via the hepatic artery and portal vein. Only 50% of the infused GSH was recovered in the effluent perfusate of perfused livers from DEN-treated rats. In contrast, significantly more GSH (80-90%) was recovered from livers from control rats or DEN-treated rats that had received AT125 pretreatment. In addition AT125 pretreatment increased the basal rates of GSH efflux in livers from DEN-treated rats. Thus, DEN-induced GGT metabolizes GSH entering the liver via the hepatic artery. Furthermore, GGT may act to decrease the net efflux of GSH from perfused livers by causing the intraorgan recycling of GSH and its constituent amino acids.
在原位灌注肝脏中，研究了致癌物处理对血液和胆汁中γ-谷氨酰转肽酶（GGT）介导的谷胱甘肽（GSH）水解为谷氨酸和半胱氨酰甘氨酸的影响。用饮用水中40 ppm的二乙基亚硝胺（DEN）或饮食中0.02%的2-乙酰氨基芴（AAF）处理大鼠50 - 60天，肝脏匀浆中的GGT活性分别增加了100%和800%。致癌物处理未影响胆汁流量以及灌注肝脏中谷氨酸和谷胱甘肽（GSH）向胆汁中的流出总量。然而，对照组、DEN处理组和AAF处理组大鼠肝脏胆汁中GSH与谷氨酸的比值分别为2.1、1.1和0.2。用L-(αS,5S)-α-氨基-3-氯-4,5-二氢-5-异恶唑乙酸（AT125）预处理可使肝脏匀浆中的GGT活性降低约85%，并使所有组胆汁中GSH与谷氨酸的比值升高至3.2。因此，灌注肝脏胆汁中GSH水解为谷氨酸与DEN和AAF处理诱导GGT的程度相关。将外源性GSH（10 μM）注入对照组、DEN处理组和AAF处理组大鼠灌注肝脏的门静脉，在流出的灌注液中可完全回收。用AT125预处理对流出灌注液中外源性GSH的回收无影响。因此，短期致癌物处理后未检测到血液空间中GSH的代谢情况。为了增加灌注液中GSH的可能水解，用DEN处理大鼠130 - 180天，并将GSH（60 μM）注入同时经肝动脉和门静脉灌注的肝脏的肝动脉。在DEN处理大鼠的灌注肝脏流出灌注液中仅回收了50%注入的GSH。相比之下，从对照组大鼠或接受AT125预处理的DEN处理大鼠的肝脏中回收的GSH明显更多（80 - 90%）。此外，AT125预处理增加了DEN处理大鼠肝脏中GSH流出的基础速率。因此，DEN诱导的GGT代谢经肝动脉进入肝脏的GSH。此外，GGT可能通过引起GSH及其组成氨基酸在器官内循环来减少灌注肝脏中GSH的净流出。
