Kempson S A, Shah S V, Werness P G, Berndt T, Lee P H, Smith L H, Knox F G, Dousa T P
Kidney Int. 1980 Jul;18(1):36-47. doi: 10.1038/ki.1980.108.
Alimentary phosphorus deprivation due to a low-phosphorus diet (LPD) elicits a profound antiphosphaturia and an increase in sodium-dependent inorganic phosphate (Pi) uptake by renal cortical brush border membrane (BBM) vesicles. But, in alimentary phosphorus deprivation due to total fasting, high urinary excretion of Pi persists. In the present study, we determined whether low tubular reabsorption of Pi in fasting is due to a diminished capacity of the specific Pi transport system with the renal cortical luminal BBM or whether it is due to a reduced transepithelial reabsorption of Pi because of metabolic conditions occurring in proximal tubule cells during fasting. Sodium-dependent Pi transport in compared with fasted rats or rats fed a normal phosphorus diet. Sodium-dependent uptake of D-glucose was significantly lower in LPD rats, compared with fast animals or animals fed a normal diet. Thus, in contrast to LPD, fasting does nt elicit an increase in Pi transport and a decrease in D-glucose transport across the isolated renal BBM. The same differences in BBM transport of Pi were present also in thyroparathyroidectomized rats. Further experiments demonstrated that the adaptation of renal function and the renal BBM transport to LPD are overridden by a subsequent period of total fasting. Results of the present study show that fasting both prevents and reverses the renal response of rats to alimentary phosphorus deprivation. The differences in Pi excretion between fasted rats, LPD rats, and LPD rats subsequently fasted are attributed, at least in part, to specific adaptive changes in sodium-dependent Pi transport across the luminal BBM, rather than to alterations in other cellular (metabolic) components of transepithelial Pi reabsorption in the proximal tubule.
低磷饮食（LPD）导致的营养性磷缺乏会引发显著的抗磷尿症，并使肾皮质刷状缘膜（BBM）囊泡对钠依赖性无机磷酸盐（Pi）的摄取增加。但是，在完全禁食导致的营养性磷缺乏中，Pi的高尿排泄持续存在。在本研究中，我们确定了禁食时Pi的肾小管重吸收降低是由于肾皮质管腔BBM中特定Pi转运系统的能力降低，还是由于禁食期间近端小管细胞中发生的代谢状况导致Pi的跨上皮重吸收减少。与禁食大鼠或喂食正常磷饮食的大鼠相比，研究了钠依赖性Pi转运。与禁食动物或喂食正常饮食的动物相比，LPD大鼠中D-葡萄糖的钠依赖性摄取显著降低。因此，与LPD相反，禁食不会引起跨分离肾BBM的Pi转运增加和D-葡萄糖转运减少。甲状旁腺切除的大鼠在BBM对Pi的转运上也存在同样的差异。进一步的实验表明，随后的完全禁食会覆盖肾功能和肾BBM转运对LPD的适应性。本研究结果表明，禁食既能预防也能逆转大鼠对营养性磷缺乏的肾脏反应。禁食大鼠、LPD大鼠和随后禁食的LPD大鼠之间Pi排泄的差异至少部分归因于跨管腔BBM的钠依赖性Pi转运的特定适应性变化，而不是近端小管中跨上皮Pi重吸收的其他细胞（代谢）成分的改变。
