Effects of flow rate, duration of stimulation and mineralocorticoids on the electrolyte concentrations of mandibular saliva from the red kangaroo (Macropus rufus)

Abstract

Mandibular saliva was collected at eight flow rates ranging between 0.052 +/− 0.0059 (S.E. of mean) and 4.294 +/− 0.0717 ml min-1 from anaesthetized red kangaroos receiving ipsilateral intracarotid infusions of acetylcholine. The concentrations of sodium (4.04 +/− 0.759 to 75.9 +/− 4.64 mmol l-1) and chloride (51.2 +/− 2.46 to 85.0 +/− 6.90 mmol l-1) and the osmolality (99.7 +/− 4.88 to 178.9 +/− 13.50 mosmol kg-1) were positively correlated with salivary flow rate over most or all of the flow range, whereas the concentrations of potassium (50.3 +/− 2.03 to 19.7 +/− 3.16 mmol l-1), calcium (5.43 +/− 1.696 to 1.26 +/− 0.055 mmol l-1), magnesium (259.8 +/− 49.3 to 19.0 +/− 1.88 mumol l-1), hydrogen ions (457.7 +/− 107.3 to 69.3 +/− 5.64 nmol l-1) and phosphate (2.22 +/− 0.171 to 0.27 +/− 0.040 mmol l-1) were negatively correlated with flow rate. Salivary bicarbonate concentration (15.6 +/− 1.76 to 21.9 +/− 1.83 mmol l-1) showed little flow dependency except possibly at high levels of stimulation. Spontaneous secretion was not observed during anaesthesia. During continuous stimulation of flow at two rates (0.5 and 2.0 ml min-1) for periods of 90 min, rest transients were observed for sodium, potassium, calcium, chloride and phosphate in the initial sample and the sodium concentration rose by 17–56% during the first 60 min of steady-state flow and stimulation. Indications that the gland was capable of responding rapidly to changes in endogenous mineralocorticoid levels were confirmed by intracarotid infusion of aldosterone at 80 micrograms h-1. With the mean salivary flow rate lying between 1.3 and 1.4 ml min-1, the salivary Na+/K+ ratio began to fall at 45–60 min of aldosterone infusion and after 4 h of infusion had fallen to 0.62 +/− 0.116. Administration of deoxycorticosterone acetate (DOCA) for 21 days at 0.25 or 0.3 mg kg-1 12 h-1 caused a further lowering of the Na+/K+ ratio to 0.09 +/− 0.013 at similar flow rates. Biopsy showed this increase to be associated with a moderate level of hypertrophy of the intralobular ducts of the gland. Two types of intralobular duct were identified on the basis of glycogen granulation after DOCA administration.(ABSTRACT TRUNCATED AT 400 WORDS)