Wideman R F
Am J Physiol. 1984 Apr;246(4 Pt 2):F373-8. doi: 10.1152/ajprenal.1984.246.4.F373.
Parathyroid hormone (PTH) stimulates a secretory component of avian renal inorganic phosphate (Pi) transport, but the secreted Pi does not appear to be derived directly from peritubular (plasma) Pi. In the present study, experiments were conducted to determine whether differences in parathyroid status during 32P infusion influenced entry of the isotope into the Pi secretory pool. Fractional excretion values for Pi (FEPi) and 32P (FE32P) were compared in normal and parathyroidectomized (PTX) anesthetized birds that had been preinfused with 32P for 0, 90, and 240 min before PTH infusion. The results demonstrate that in the absence of exogenous PTH, FEPi is identical to FE32P in normal and PTX birds, reflecting full equilibration of 32P with excreted Pi under these conditions; and, regardless of the duration of 32P preequilibration or the parathyroid status of the experimental animals, exogenous PTH always causes FEPi to exceed FE32P. It is concluded that the Pi secretory pool is inaccessible to 32P under conditions that should markedly alter cellular Pi influx and efflux.
甲状旁腺激素（PTH）刺激禽类肾脏无机磷酸盐（Pi）转运的分泌成分，但分泌的Pi似乎并非直接来源于肾小管周围（血浆）Pi。在本研究中，进行了实验以确定在注入32P期间甲状旁腺状态的差异是否会影响该同位素进入Pi分泌池。在注入PTH前分别预注入32P 0、90和240分钟的正常和甲状旁腺切除（PTX）麻醉鸟类中，比较了Pi（FEPi）和32P（FE32P）的排泄分数值。结果表明，在没有外源性PTH的情况下，正常和PTX鸟类的FEPi与FE32P相同，这反映了在这些条件下32P与排泄的Pi完全平衡；并且，无论32P预平衡的持续时间或实验动物的甲状旁腺状态如何，外源性PTH总是导致FEPi超过FE32P。得出的结论是，在应显著改变细胞Pi流入和流出的条件下，32P无法进入Pi分泌池。
