Control of phosphate appetite in young rats.

In the present study, we investigated whether a diet deficient in inorganic phosphate (Pi) stimulates an ingestive behavior to seek sources of Pi. Male Wistar rats were placed in individual cages with unrestricted access to tap water and a low (LPD, 0.02% Pi) or normal (NPD, 0.6% Pi) Pi diet for 6 days. On day 7, LDP rats were given unlimited access to a solution of 25 mM potassium phosphate water (Pi-water) for 9 additional days. Rats fed LPD consumed 70-100% more Pi-water then those fed NPD. The increase in Pi-water intake resulted in a marked rise in the growth rate of rats fed LPD during day 9. A similar intake of Pi was induced after only 2 days of LPD and was associated with significant reductions in both plasma and cerebrospinal fluid (CSF) levels of Pi; these levels remained low throughout Pi restriction, despite a significant intake of Pi-water. Replenishment with a high-Pi diet rapidly quenched the appetite for Pi-water and was associated with restoration of both plasma and CSF Pi levels. These findings suggest that an appetite for Pi can be induced in rats, perhaps through lowered plasma and CSF Pi levels.