Renal phosphate excretion in goats

It was the aim of these experiments to characterize further the role of salivary glands and kidneys in phosphate (Pi) homeostasis of small ruminants. Renal clearance experiments were performed in five female, non-pregnant adult goats during infusions of physiological NaCl or isotonic phosphate solution. Basal plasma Pi concentrations of 1.6 +/- 0.3 mM (NaCl infusion) were associated with a renal resorption of the filtered Pi by 98.5-99.3% and Pi was excreted in the urine at a rate of 1.2-2.8 mumol/min. Elevating the plasma Pi levels up to 7.2 +/- 1.7 mM resulted in significant increases of Pi excretion. The mean plasma threshold for renal Pi excretion of these animals was high (4.3 +/- 1.0 mM) and thus substantially higher than the physiological range of plasma Pi. The maximal tubular resorption rate for Pi in goats was found to be higher than the respective values in monogastric animals. In relation to the enhanced Pi concentrations in plasma the salivary Pi concentrations increased simultaneously and reached a maximum level of about 66.3 mM at plasma levels between 4-6 mM. Indications for hormonal regulation mechanisms via parathyroid hormone (PTH) and calcitriol could not be detected during the infusion periods.