<p> Intestinal phosphorus absorption is a key
contributor to the body phosphorus pool, but much is unknown regarding
physiological adaptations in intestinal phosphorus absorption that occur in
vivo. We sought to measure changes in intestinal phosphorus absorption efficiency
and phosphorus balance in adolescent females and in rats in response to several
factors, using physiologically relevant assessment approaches including
whole-body phosphorus balance techniques and <i>in situ</i> ligated intestinal loop absorption methods.</p>
<p> We
first assessed phosphorus balance and net phosphorus absorption in female
adolescents from a controlled crossover study with two levels of calcium
intake. Despite an increased calcium intake of 600 mg/day, there was no change
in phosphorus balance, nor a significant change in net phosphorus absorption.</p>
<p> Next,
we measured intestinal phosphorus absorption efficiency with the <i>in situ</i> ligated loop method in healthy
Sprague Dawley rats as well as the Cy/+ rat model of progressive kidney
disease. We found 10-week-old healthy rats had a small but higher absorption
efficiency of phosphorus compared to 20- and 30-week-old rats, while 20-week
Cy/+ rats had higher absorption efficiency than 30-week-old. Each of these
results corresponded to net phosphorus absorption from balance as well as the
concentration of 1,25-dihydroxyvitamin D3. In healthy rats, there was no effect
of altering the level of phosphorus in the diet on absorption efficiency. In
Cy/+ rats, kidney disease produced a small <i>increase</i>
in absorption efficiency, contrary to the predicted decrease that would occur
with lower 1,25-dihydroxyvitamin D3 observed in CKD. Gene expression of the
major intestinal phosphate transporter, NaPi-2b, largely followed absorption
patterns.</p>
<p> The
utility of the Cy/+ model is limited to males as females do not begin to show
signs of progressive kidney decline until a much older age. Therefore, we
sought to test whether ovariectomy would accelerate kidney disease in Cy/+
females, with the aim of establishing a postmenopausal model of progressive
kidney disease. Our results show that kidney disease is not accelerated by
ovariectomy in this rat strain, as measured by kidney weight and biochemistries
including blood urea nitrogen, creatinine, creatinine clearance, and plasma
phosphorus and calcium.</p>
<p> Our
results utilizing <i>in situ</i> absorption
measures as well as net absorption of phosphorus suggest that some of the factors
that are understood to influence the intestinal absorption of phosphorus do not
have a significant influence in a physiological context.</p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/7503842 |
| Date | 10 May 2019 |
| Creators | Colby J Vorland (6114410) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/The_Physiological_Relevance_of_the_Adaptive_Capacity_of_Intestinal_Phosphorus_Absorption/7503842 |
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