Effect of Diet and Mineralocorticoid Administration on the Concentration of Anions in Parotid-Saliva From the Red Kangaroo, Macropus-Rufus

Abstract

The composition of parotid saliva from six red kangaroos was compared after they had been fed for 21 days with supplement pellets plus chaff, with chaff only, and with chaff plus injections of deoxycorticosterone acetate (DOCA) at 0.25 or 0.3 mg kg-' every 12 h. DOCA administration caused a marked reduction in sodium concentration and increase in potassium concentration (Na:K ratio of from 0.17�0.097 to 4.68�0.749 depending on flow rate) and an overall reduction in total cation concentration; salivary chloride concentration and osmolality were also reduced. Partial replacement of the chaff diet with supplement pellets produced significantly higher salivary bicarbonate and lower phosphate concentrations. No relationship between salivary bicarbonate concentration and arterial pCO2, plasma bicarbonate concentration or the rate of acetylcholine infusion was found which might indicate the cause of the anion changes. Similarly, no causal relationship was observed between salivary phosphate concentration and arterial plasma phosphate concentration or dietary phosphate intake. Dietary intakes of calcium and magnesium, and the plasma and salivary concentrations of these ions, were similar under the three experimental regimes. The diet-induced changes in salivary bicarbonate and phosphate were not associated with differences in dietary intake of dry matter, organic matter, crude protein or neutral detergent fibre, but may have been related to concurrent changes in intake of one or more subcomponents of dietary fibre.