Abraham M I, Woods R E, Breedlove D K, Kempson S A
Department of Physiology and Biophysics, Indiana University School of Medicine, Indianapolis 46202-5120.
Am J Physiol. 1992 May;262(5 Pt 2):F731-6. doi: 10.1152/ajprenal.1992.262.5.F731.
Insulin stimulates the Na(+)-Pi cotransport system in the brush-border membrane (BBM) of the renal proximal tubule, and an acute decrease in plasma insulin leads to a decrease in renal reabsorption of Pi. It has been proposed that insulin may play a role in the rapid renal adaptation to dietary deprivation of Pi. This hypothesis was tested using rats with low plasma insulin due to streptozotocin-induced diabetes. Both control and diabetic rats were housed in metabolic cages and fed either a normal Pi diet or a low Pi diet for 3 days. At the end of the third day, BBM vesicles were prepared from renal cortex and Na(+)-Pi cotransport was measured. At the whole kidney level, diabetic rats showed a normal adaptive response. There was a prompt and marked decrease in urinary Pi excretion when the rats ate a low Pi diet. At the BBM level, however, the adaptive response was absent. There was no increase in Na(+)-Pi cotransport in diabetic rats fed low Pi diet. Treatment of diabetic rats with exogenous insulin before feeding low Pi diet restored the adaptive increase in Pi transport by BBM. Insulin appears to be required for the adaptation of proximal tubule Pi transport to low Pi diet. In the absence of this adaptation in proximal tubule BBM, a compensatory response in the kidney may produce an increase in Pi reabsorption in later segments of the nephron.
胰岛素可刺激肾近端小管刷状缘膜（BBM）中的钠 - 磷共转运系统，血浆胰岛素的急性减少会导致肾脏对磷的重吸收减少。有人提出胰岛素可能在肾脏对低磷饮食的快速适应性调节中发挥作用。本研究利用链脲佐菌素诱导糖尿病导致血浆胰岛素水平降低的大鼠对这一假说进行了验证。将对照大鼠和糖尿病大鼠置于代谢笼中，分别给予正常磷饮食或低磷饮食3天。在第三天结束时，从肾皮质制备BBM囊泡并测定钠 - 磷共转运。在全肾水平，糖尿病大鼠表现出正常的适应性反应。当大鼠食用低磷饮食时，尿磷排泄迅速且显著减少。然而，在BBM水平，适应性反应缺失。喂食低磷饮食的糖尿病大鼠钠 - 磷共转运没有增加。在喂食低磷饮食前用外源性胰岛素治疗糖尿病大鼠可恢复BBM对磷转运的适应性增加。胰岛素似乎是近端小管磷转运适应低磷饮食所必需的。在近端小管BBM缺乏这种适应性的情况下，肾脏的代偿反应可能会导致肾单位后期节段对磷的重吸收增加。
