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Phosphate
The total body content of phosphate is 320 mmol/kg. Eighty-five percent of the body’s phosphate content is present in the bones and teeth; the rest is widely distributed in the cells.
Functions of Phosphate
- Helps in the development of bone and teeth.
- Helps in the metabolism of fat and carbohydrate (phosphorylation).
- Helps in the formation of adenosine triphosphate (ATP).
- Helps in the formation of nucleic acids.
Dietary Intake
The RDA of phosphate is around 550 mg/day but has to be increased in pregnant and lactating females (around 1,000 mg/day). Some of the rich sources of phosphate are milk, meat, fruits and vegetables.
Phosphate Absorption
- Phosphate absorption occurs in the gastrointestinal tract through paracellular absorption and transcellular transport.
- The paracellular pathway does not saturate and has a significantly higher absorption capacity than does the transcellular pathway.
- Evidence indicates that this pathway is the primary mechanism of intestinal phosphate absorption, particularly with Western diets containing high amounts of phosphorus.
- Elevated serum phosphorus concentrations are associated with cardiovascular morbidity and mortality but serum phosphorus concentrations > 5.5 mg/dL are highly prevalent despite best efforts with dietary phosphate restriction, dialysis, and the use of phosphate binders.
- The efficacy of phosphate binders may be inherently limited because the mechanism of action does not target any phosphate absorption pathway.
- Thus, therapeutic innovations are needed to address the limitations of phosphate binders.
- Phosphate absorption inhibitors that target the pathway are a novel therapeutic class.
- Tenapanor is an investigational first-in-class nonbinder phosphate absorption inhibitor that inhibits the sodium-hydrogen exchanger isoform 3 to reduce paracellular permeability specific to phosphate.
- Phosphate absorption inhibitors may represent a new mechanistic approach to phosphate management with the potential to improve clinical outcomes.
Phosphate Excretion
- Phosphorus is mainly excreted in the urine as phosphates of various cations. Faecal phosphates are excreted in the form of calcium phosphate.
- Ninety percent of phosphates are reabsorbed in the proximal convoluted tubule. Parathormone decreases renal tubular reabsorption of phosphates.
Blood Phosphorus Concentrations
The normal blood level of phosphorus is 2–4 mg/100 mL in adults.
