Interaction between substance P and beta-adrenergic agonists in the modulation of the secretion of fluid and protein by the rat submandibular gland.

The interactions between substance P and beta-adrenergic agonists such as isoprenaline, dobutamine and terbutaline in the control of the secretion of fluid and protein from the rat submandibular gland have been examined. Substance P elicited large volumes of saliva whereas isoprenaline, dobutamine and terbutaline elicited small volumes only. The secretion of fluid in response to substance P was markedly enhanced when substance P was administered in combination with isoprenaline or dobutamine but not when it was administered in combination with terbutaline. Isoprenaline elicited large amounts of protein, whereas substance P elicited small amounts. The secretion of protein in response to isoprenaline did not change when isoprenaline was administered in combination with substance P. The secretion of fluid and protein induced by substance P in combination with isoprenaline was antagonized by metoprolol and by spantide, but it was unaffected by pretreatment with ICI118551. These results suggest that in the rat submandibular gland stimulation of beta1-adrenoceptors but not of beta2-adrenoceptors potentiates the secretion of fluid that is induced by stimulation of tachykinin receptors, whereas stimulation of tachykinin receptors does not enhance the secretion of protein that is induced by stimulation of beta1-adrenoceptors.