Phosphorus homeostasis in sheep. I. Effects of ligation of parotid salivary ducts

Abstract

The effects of bilateral parotid duct ligation upon calcium and phosphorus concentrations in blood plasma and upon phosphorus excretion in urine and faeces have been examined. Five Merino wethers were used, of which three were given a phosphorus-deficient diet (0.304 g phosphorus/day) and two a phosphorus-sufficient diet (1.454 g phosphorus/day) for 32 days prior to ligation of the parotid ducts. Blood samples were taken every 6 hours for 2 days before and 4 days after parotid duct ligation followed by less frequent sampling for a further 3 days. Parotid duct ligation caused an increase in plasma inorganic phosphorus levels after the first day in the phosphorus-supplemented sheep and in one of the deficient animals. Plasma calcium concentrations tended to be inversely related to plasma phosphorus levels and showed marked variations on the fourth day following duct ligation, coinciding with a sudden fall in plasma phosphorus levels of 30-50 %. Urinary phosphorus excretion in the phosphorus-sufficient animals was increased 20 to 50-fold following ligation and reached a peak of about 600 mg/day on the fourth day, but there was no significant change in phosphorus balance. Marked alterations in the daily urinary output of phosphorus tended to be associated with a change in plasma phosphorus levels in the reverse direction. Four of the sheep were re-examined 22 months after duct ligation and the elevated urinary output of phosphorus was found to have persisted in three of the four animals. It appears that there is a relationship between the salivary secretion of phosphorus to the gut and the urinary phosphorus excretion which contributes towards maintenance of the phosphorus homeostasis in sheep.