Response of the parotid gland of red kangaroos,Macropus rufus,to phenylephrine stimulation

Intracarotid infusions of l-phenylephrine at 1.0 or 10 nmol kg(-1) min(-1) were accompanied by increases in salivary amylase activity, protein, potassium, magnesium and chloride relative to cholinergically-stimulated saliva. Intravenous infusions of phenylephrine at the same dose rates had a lesser effect on salivary composition particularly protein. Propranolol administered with phenylephrine via the carotid artery, at an antagonist/agonist ratio of 10:1, was much more effective in blocking the phenylephrine-induced changes in salivary composition than equimolar infusion of phentolamine with phenylephrine. It was concluded that alpha(1)-adrenoreceptors were not present in functionally significant numbers in the gland and that the effect of phenylephrine on the kangaroo parotid was mediated by beta-adrenoreceptors. As the phenylephrine dose rates in the kangaroos were comparable with those used to determine alpha-adrenergic responses of eutherian salivary glands and as phentolamine appeared to have minor beta-sympathomimetic activity, at least one subtype of beta-adrenoreceptors in macropods may not be identical to its eutherian counterpart.