RESPONSE OF THE PAROTID-GLAND OF THE BRUSHTAIL POSSUM, TRICHOSURUS-VULPECULA, TO ADRENERGIC-STIMULATION

Adrenergic stimulation of parotid secretion was investigated in anaest hetised brushtail possums to ascertain fluid secretion rates and saliv ary composition. Because neither alpha- nor beta-adrenergic stimulatio n evoked saliva output, infusion of the adrenergic agonists was superi mposed on a pre-existing bethanechol-stimulated flow. Isoprenaline inf usion (2.4 nmol min(-1)) increased salivary amylase activity, [protein ]; [HCO3]; [PO4] and [Ca], and amylase/Ca and protein/Ca ratios; reduc ed [Cl]; [K] and osmolality; but did not alter H+ activity; [urea]; [N a]; [Mg]; amylase/protein or saliva/plasma urea ratios. These data are consistent with isoprenaline stimulating acinar secretion of protein, Ca and PO4 but not the ion transport necessary for primary fluid form ation at the endpieces and modifying transport of monovalent ions in t he excurrent ducts. Consequently, the possum parotid has beta-adrenerg ic receptors in both the endpieces and excurrent ducts. Phenylephrine infusions at 2.4 and 24 nmol min(-1) were without effect whereas pheny lephrine at 240 nmol min(-1) caused changes in salivary composition wh ich paralleled those for isoprenaline administration but were generall y of lesser magnitude. Thus, the possum parotid has few or no alpha-ad renergic receptors and the salivary response elicited was the result o f cross-reaction of phenylephrine with beta-adrenergic receptors. (C) 1998 Elsevier Science Inc. All rights reserved.