Department of Nutrition Science, Purdue University, West Lafayette, IN, United States of America.
Division of Nephrology, Department of Medicine, Indiana University School of Medicine, Indianapolis, IN, United States of America.
PLoS One. 2018 Nov 19;13(11):e0207601. doi: 10.1371/journal.pone.0207601. eCollection 2018.
Intestinal phosphorus absorption is an important component of whole-body phosphorus metabolism, and limiting dietary phosphorus absorption is particularly of interest as a therapeutic target in patients with chronic kidney disease to manage mineral bone disorders. Yet, mechanisms and regulation of intestinal phosphorus absorption have not been adequately studied and discrepancies in findings exist based on the absorption assessment technique used. In vitro techniques show rather consistent effects of dietary phosphorus intake level and age on intestinal sodium-dependent phosphate transport. But, the few studies that have used in vivo techniques conflict with these in vitro studies. Therefore, we aimed to investigate the effects of dietary phosphorus intake level on phosphorus absorption using the in situ ligated loop technique in three different aged rats. Male Sprague-Dawley rats (n = 72), were studied at 10-, 20-, and 30-weeks-of-age on a low (0.1%), normal (0.6%), or high (1.2%) phosphorus diet in a 3x3 factorial design (n = 8/group). Rats were fed their assigned diet for 2-weeks prior to absorption testing by jejunal ligated loop as a non-survival procedure, utilizing 33P radioisotope. Metabolic cages were used for determination of calcium and phosphorus balance over the final four days prior to sacrifice, and blood was collected at the time of sacrifice for biochemistries. Our results show that phosphorus absorption was higher in 10-week-old rats compared with 20- and 30-week-olds and this corresponded to higher gene expression of the major phosphate transporter, NaPi-2b, as well as higher whole-body phosphorus balance and net phosphorus absorption. Dietary phosphorus intake level did not affect jejunal phosphorus absorption or NaPi-2b gene expression. Our results contrast with studies utilizing in vitro techniques, but corroborate results of other rodent studies utilizing in situ or in vivo methods. Thus, there is need for additional studies that employ more physiological methods of phosphorus absorption assessment.
肠道磷吸收是全身磷代谢的重要组成部分，限制膳食磷吸收特别作为治疗慢性肾脏病患者矿物质骨代谢紊乱的靶点引起关注。然而，肠道磷吸收的机制和调节尚未得到充分研究，并且基于所使用的吸收评估技术存在发现的差异。体外技术显示饮食磷摄入水平和年龄对肠道钠依赖性磷酸盐转运具有相当一致的影响。但是，少数使用体内技术的研究与这些体外研究相冲突。因此，我们旨在使用原位结扎环技术在三种不同年龄的大鼠中研究饮食磷摄入水平对磷吸收的影响。雄性 Sprague-Dawley 大鼠（n = 72），在 10、20 和 30 周龄时，采用低（0.1%）、正常（0.6%）或高（1.2%）磷饮食进行 3x3 析因设计（n = 8/组）。大鼠在吸收测试前 2 周接受指定饮食喂养，通过空肠结扎环进行非存活程序，利用 33P 放射性同位素。代谢笼用于在处死前最后四天确定钙和磷平衡，并且在处死时采集血液用于生物化学。我们的结果表明，10 周龄大鼠的磷吸收高于 20 周龄和 30 周龄大鼠，这与主要磷酸盐转运体 NaPi-2b 的基因表达较高，以及全身磷平衡和净磷吸收较高相对应。饮食磷摄入水平不影响空肠磷吸收或 NaPi-2b 基因表达。我们的结果与利用体外技术的研究相反，但与利用原位或体内方法的其他啮齿动物研究的结果相符。因此，需要进行更多的研究，采用更生理的磷吸收评估方法。
