PubMed1985
Saliva was elicited from rat salivary glands by terbutaline at i.p. doses of 1, 5, 10 and 25 mg/kg b.wt. but not by doses of 0.1 or 0.5 mg/kg b.wt. Dobutamine elicited no secretion at 1 or 2 mg/kg but did at 5, 10 and 25 mg/kg b.wt. At 5 mg/kg terbutaline evoked nearly maximal volumes but with dobutamine, volumes were small at this dosage. At dosages of 10 and 25 mg/kg volumes with the two agonists were similar for parotid, but with submandibular, the volumes evoked by dobutamine were nearly two times as high as those elicited by terbutaline. Mean [Ca] of parotid saliva was also similar at all dosages of dobutamine (approximately 12 mEq/liter) and generally similar at all dosages of terbutaline (11-15 mEq/liter). Mean [Ca] of dobutamine-elicited submandibular saliva was approximately 6, 7 and 8 mEq/liter at 5, 10 and 25 mg/kg b.wt, respectively. With parotid, [Ca] was approximately 10 mEq/liter at 1, 5 and 10 mg/kg b.wt. but increased to 16-18 mEq/liter at 25 mg/kg. The time course of calcium secretion is described for both agonists at each dosage. [Ca] of both glands was decreased 60 min after i.p. injection of 10 or 25 mg/kg doses of dobutamine or terbutaline but was not changed by 5 mg/kg doses. Administration of 10 mg/kg of atenolol, the selective beta 1 antagonist, 20 min prior to injection of a 10 mg/kg dose of either terbutaline (beta 2 agonist) or dobutamine (beta 1 agonist) blocked secretion from both glands, and prevented the usual agonist-induced reduction in glandular concentration of calcium. Butoxamine, on the other hand, did not modify effects of terbutaline on fluid secretion or depletion of glandular calcium; it did partially inhibit dobutamine-induced fluid and calcium secretion but not depletion of glandular calcium. The present data suggest that beta adrenoceptors of salivary glands are predominantly of the beta 1 subtype and that it is these that regulate calcium and fluid secretion. On the basis of the data with the antagonists, it is concluded that terbutaline activates beta 1 rather than beta 2 receptors since the beta 1 antagonist but not the beta 2 antagonist blocked secretory responses to terbutaline.