Abstract
The rabbit is a much-used experimental animal in renal tubule physiology studies. Although a monogastric mammal, the rabbit is a known hindgut fermenter. That ruminant species excrete inorganic phosphate (Pi) mainly through the digestive system while non-ruminants eliminate surplus phosphate primarily through the renal system are acknowledged facts. To understand phosphate homeostasis in the acidotic rabbit, anaesthetized animals were infused with hydrochloric acid, after which they underwent intravenous phosphate loading. Biofluids were collected during the infusion process for analysis. Plasma Pi increased (7.9 ± 1.7 mmoles.Litre−1 (N = 5) vs 2.2 ± 0.4 mmoles.Litre−1 (N = 10) pre-infusion, (p < 0.001)), while urinary phosphate excretion was also enhanced (74.4 ± 15.3 from a control value of 4.7 ± 3 µmol.min−1 (N = 9), pre-infusion, p < 0.001)) over an 82.5 minute Pi loading period. However, the fractional excretion of Pi (FePi) only increased from 14.2 ± 5.4% to a maximum of 61.7 ± 19% (N = 5) over the infusion period. Furthermore, the renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmPi/GFR) computed to 3.5 mmol.L−1, while a reading of 23.2 µmol.min−1.Kg.0.75 was obtained for the transport maximum for Pi (TmPi). The high reabsorptivity of the rabbit nephrons coupled with possibly a high secretory capacity of the salivary glands for Pi, may constitute a unique physiological mechanism that ensures the rabbit hindgut receives adequate phosphate to regulate caecal pH in favour of the resident metabolically - active microbiota. The handling of Pi by the rabbit is in keeping with the description of this animal as a monogastric, pseudo-ruminant herbivore.
Highlights
The rabbit is a much-used experimental animal in renal tubule physiology studies
After absorption in the gut, phosphorous is transported across cell membranes, as inorganic phosphate (Pi), by means of a secondary active transport process, wherein it exists as the main intracellular anion. 80–85% of total body phosphate is located within bone, while ~15% is present within cells
Urine was collected at 15-minute intervals during the course of inorganic phosphate loading of the acidotic rabbits
Summary
The rabbit is a much-used experimental animal in renal tubule physiology studies. a monogastric mammal, the rabbit is a known hindgut fermenter. The renal tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmPi/GFR) computed to 3.5 mmol.L−1, while a reading of 23.2 μmol.min−1.Kg.0.75 was obtained for the transport maximum for Pi (TmPi). The rabbit (Oryctolagus cuniculus) has an organ called the caecum that functions in a similar fashion to that of the rumen in a cow Unlike ruminants, this fermentation vessel in the rabbit is positioned not proximal to, but is located distal to the small intestine. After absorption in the gut, phosphorous is transported across cell membranes, as inorganic phosphate (Pi), by means of a secondary active transport process, wherein it exists as the main intracellular anion. The regulation of plasma phosphate levels is governed by a set of complex activities taking place in a series of feedback loops, involving the parathyroid gland – gut - bone – kidney axis[4]. These include the SLC34 family (NaPi-IIa & NaPi-IIc) and the SLC20 family (PiT-1& PiT-2), respectively[7,8]
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call