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Evidence for induction of a phosphate appetite in juvenile rats
J M Sweeny1, H E Seibert, C Woda
1Department of Physiology and Biophysics, Georgetown University School of Medicine, Washington, District of Columbia 20007, USA.
Insights
Dietary phosphate restriction in juvenile rats induced a strong appetite for phosphate, increasing intake and growth rates. This appetite, possibly driven by low phosphate levels, helps ensure adequate nutrient supply for development.
Area of Science:
- Physiology
- Nutritional Science
- Behavioral Biology
Background:
- Juvenile animals have high metabolic demands for growth.
- Phosphate is crucial for growth and development.
- Understanding appetite regulation is key to nutritional science.
Purpose of the Study:
- To investigate if dietary phosphate restriction stimulates phosphate appetite in juvenile rats.
- To determine the physiological and behavioral responses to phosphate deficiency.
Main Methods:
- Juvenile Wistar rats were fed either a low phosphate diet (LPD) or a normal phosphate diet (NPD).
- Rats were given access to phosphate-rich water (PiH2O) to assess intake.
- Plasma and cerebrospinal fluid (CSF) phosphate levels were measured.
- Renal phosphate reabsorption (TmPi) was assessed.
Main Results:
- Rats on LPD consumed 70-100% more PiH2O than NPD rats.
- Phosphate restriction led to increased growth rates and phosphate intake.
- Low plasma and CSF phosphate levels persisted despite increased PiH2O intake.
- Renal phosphate reabsorption remained elevated during restriction.
Conclusions:
- Phosphate restriction induces a phosphate appetite in juvenile rats, likely mediated by reduced plasma and CSF phosphate levels.
- This appetite serves as a crucial mechanism to maintain adequate phosphate supply for growth.
- Dietary interventions can modulate nutrient-specific appetites, impacting development.
Abstract:
This study examined whether dietary phosphate (Pi) restriction stimulates an appetite for Pi in the juvenile rat, which normally has a high metabolic Pi demand for growth. Juvenile Wistar rats were placed in individual cages with unrestricted access to tap water and a low (LPD, 0.02% Pi) or normal Pi diet (NPD, 0.6% Pi) for 7 days. On day 8, both groups of rats were given unlimited access to a solution of 0.3 M potassium phosphate water (PiH2O) for 8 additional days. Rats fed LPD consumed 70-100% more PiH2O then those rats fed NPD (P < 0.001). The increase in PiH2O intake resulted in a marked rise in the growth rate of rats fed LPD during days 8-15. A similar Pi intake was inducible after only 2 days of LPD and was associated with significant reductions in both plasma and cerebrospinal fluid (CSF) Pi levels; these levels remained low throughout Pi restriction, despite a significant PiH2O intake. Furthermore, the renal adaptation to enhance Pi reabsorption (TmPi) during Pi deprivation remained elevated despite enhanced PiH2O intake. Replenishment with a high-Pi diet rapidly quenched the PiH2O appetite and was associated with restoration of both plasma and CSF Pi levels. These findings suggest that an appetite for Pi can be induced in juvenile rats, perhaps through lowered plasma and CSF Pi levels. This behavioral response may serve as an additional mechanism to maintain an adequate supply of Pi necessary for growth and development of the animal.
