Volume and Composition of Pilocarpine- and Isoproterenol-stimulated Submandibular Saliva of Early Postnatal Rats

Abstract

Submandibular saliva was collected from early postnatal rats by cannulation of the main excretory duct of individual glands after i.p. injections of pilocarpine (10 mg/kg body weight) or isoproterenol (10 mg/kg body weight). With this method of saliva collection, a secretory response to pilocarpine was observed at two wk of age. The average weight of 40 glands was 35.6 +/- 1.6 mg, and the average volume of saliva secreted in 60 min was 32 +/- 2.2 microliters. By three wk of age, the gland had approximately doubled in size (average weight of 39 glands = 61.9 +/- 3.1 mg), and the average total volume of saliva secreted in 60 min was more than three times larger (120.4 +/- 10.5 microliters) than that secreted by two-week-old rats. The relationship between electrolyte (Na+, K+, Ca++) and protein concentrations and rate of flow was similar to that observed in pilocarpine-stimulated adult saliva, and did not differ appreciably in the saliva of two- and three-week-old animals. A measurable secretory response to isoproterenol was observed at three wk of age when saliva was collected by duct cannulation. The average total volume of saliva secreted in 60 min was 48 +/- 3.1 microliters, and salivary Na+ and K+ concentrations, and their relationship to flow rate, were similar to those of isoproterenol-stimulated adult saliva. Saliva Ca++ and protein concentrations were also generally similar to those of isoproterenol-stimulated adult saliva. Total protein output (in 60 min) was 2 1/2 times greater in three-week-old rats with isoproterenol stimulation (compared to pilocarpine stimulation), but was significantly smaller than that of isoproterenol-stimulated adult glands. It is concluded that the submandibular gland of early postnatal rats is capable of secreting saliva in vivo following cholinergic and beta-adrenergic stimulation, and that this ability corresponds with the appearance of the corresponding autonomic receptors, but precedes cytodifferentiation. Ductal transport of electrolytes is well-developed at this stage of postnatal development, but fluid and protein output is smaller than in adult glands and requires full morphological maturation of acinar cells.