The effect of beta-sympathomimetic stimulation on parotid salivation in the red kangaroo (Macropus rufus)

Salivation was stimulated by intracarotid isoprenaline infusion given alone or combined with acetylcholine. By itself, isoprenaline (0.12-1.2 nmol kg-1 min-1) stimulated flow rates of 0.037-0.233 ml min-1 (2.77-10.5 microliters/g gland per min). Salivary Na, Cl, PO4 and total solute concentrations were positively correlated with flow; K, Mg and urea were negatively correlated with flow; and Ca, H+, HCO3, protein and amylase activity were not correlated with flow. Relative to cholinergic saliva, isoprenaline-evoked saliva had higher levels of amylase activity, urea, protein, K, Mg, H+, PO4 and Cl but lower osmolality, Na, Ca and HCO3. At a steady flow (1 ml min-1), isoprenaline infusion (0.3 nmol kg-1 min-1) superimposed on a pre-existing acetylcholine infusion increased salivary amylase activity, protein, urea, K, Mg, Cl and PO4, reduced HCO3 and did not alter Na, Ca, H+ and osmolality. Superimposition of isoprenaline infusion (0.5 nmol kg-1 min-1) on a low-level acetylcholine infusion increased flow rate by 400-900%. Excretion rates of K, Mg, Cl and PO4 were higher and Ca lower than predicted for saliva secreted at equivalent flows during acetylcholine stimulation. Na, H+ and HCO3 were as predicted for the same flow rate under cholinergic stimulation. The simplest coherent interpretation of these data is that isoprenaline affects transport of protein and ions at the end organs, but has little effect on the resting transport characteristics of the striated and excretory ducts of the kangaroo parotid, in accord with the known nerve distribution of this gland.