Growth of rat salivary glands after terbutaline or dobutamine

Abstract

Six days after commencement of a regimen of twice daily administration of 25, 50, or 75 mg/kg body wt doses of the beta 1 adrenergic agonist, dobutamine, or the beta 2 adrenergic agonist, terbutaline, submandibular and parotid glands of rats were enlarged in size. The beta 1 receptor was responsible for mediation of these changes with both agonists, since the effects of either agonist were prevented when a 10 mg/kg dose of the beta 1 antagonist, atenolol, was injected 20 min prior to the agonists but were not prevented when the beta 2 antagonist butoxamine, was given prior to each agonist. The increase in gland size caused by dobutamine was more marked than that induced by terbutaline; total amount of DNA of the parotid gland was also higher with dobutamine than with terbutaline. The response of the parotid gland to each dose of either agonist was greater than that of the submandibular gland, suggesting that the parotid gland has more beta receptors than does submandibular gland. The data also show that the increase in cell size precedes an increase in cell number. The increase in cell size depends on activation of fewer receptors than are required for the increase in DNA, since at the same dose of dobutamine, e.g., increase in cell size but not cell number was observed; moreover, the same dosage effected an increase in DNA of parotid but not submandibular gland. The data thus show that enlargement of both glands, as well as increase in size and number of their acinar cells, is dependent on activation of beta 1 adrenoceptors only.