A comparative study of the effects of four choline esters on the secretion of fluid and glycoprotein from rat submandibular glands.

The actions of four choline esters, acetylcholine (ACH), methacholine (MET), carbachol (CAR) and bethanechol (BET), on the secretion of saliva and the specific glycoprotein (GP) contained in the secretory cells of the submandibular gland (SMG) of the rat were compared under conditions with and without physostigmine (PHY). The ED50 values with respect to salivation were 17 mg/kg for ACH, 1060 micrograms/kg for BET, 810 micrograms/kg for MET and 75 micrograms/kg for CAR, whereas after pretreatment with PHY, ED50 values were lowered to 7.5 mg/kg for ACH and 212 micrograms/kg for MET, but remained unchanged for CAR and BET. SDS-polyacrylamide gel electrophoresis demonstrated that the saliva from the SMG elicited by the four choline esters contained GP I (130 KDa) and GP IV (21.5 KDa), characteristic of the acinus, and a band of GP III (31 KDa), which originates from the granular tubules. The order of intensity of these bands was band I much greater than band III = band IV. Among these bands, band I increased in intensity in a dose-dependent manner. These results suggest that the four choline esters act mainly on the acinar cells, but exert some effects on the granular tubules of the rat SMG.