Abstract-The effects of substance P, neurokinin A, physalamine, and eledoisin on the secretion of fluid and glycoproteins from the submandibular glands of various rodents were investigated.Following i.v. injection of each peptide at a dose of 20 ,ug/kg, the major glycoprotein species secreted from rats and guinea pigs were shown to be electrophoretically identical with those found in the acini. However, saliva was not elicited from the mice and hamsters.These results suggest that in both rats and guinea pigs, tachykinins act on the acinar cells of the submandibular gland only.Substance P (SP), neurokinin A (sub stance K, NKA), neurokinin B (NKB), neuro peptide K (NPK) and neuropeptide r (NPr), of mammalian origin, and physalamine, eledoisin and kassinin, of non-mammalian origin, have stimulative action on the salivary secretion in rats (1-4). Pernow described that SP is a potent stimulator of salivation in the hamster, guinea pig, dog and hen as well as rat but not in the cat or rabbit (5). However, the sialogogic action of tachykinins except SP on rodents such as mouse, hamster and guinea pig has not been observed.It is well-known that the secretory cells of the submandibular gland differ in morphology and functions among rodents. We reported previously that SP acts on the acinar cells of the rat submandibular gland and stimulates secretion of glycoproteins from the cells (6).The present study was carried out to elucidate the effects of four tachykinins, SP, NKA, physalamin, eledoisin on the secretion of fluid from the submandibular glands of the rat, mouse, hamster and guinea pig. In ad dition, the action site of tachykinins on the submandibular glands was examined.Adult male rats (Sprague Dawley, 300 350 g), mice (ddY, 30-35 g), hamsters (Syrian, 100-120 g) and guinea pigs (Hartley, 500-600 g) were used. The animals were deprived of food but given water ad libitum for 24 hr prior to the experiments. Animals were anesthetized with urethane (1.5 g/kg), and then cannulation of the trachea and ligation of ducts of the sublingual glands were performed. After i.v. injection of SP, NKA, physalamin (Protein Research Foun dation, Osaka, Japan) or eledoisin (Sigma Chemical Co., St. Louis, MO, U.S.A.) at a dose of 20 #g/kg, respectively, saliva from the submandibular glands was collected over successive intervals of 1 min for the first 5 min and thereafter over 5-min intervals until 20 min had elapsed. Secretory segments of acini and granular tubules from normal animals were collected by the microdissection method of Masuhara and Iwabuchi (7). Each secre tory segment was dissolved in 6% sodium dodecyl sulphate (SDS) that contained 10% 2-mercaptoethanol and then heated at 90°C for 3 min. The protein contents in the saliva and segments were determined by Lowry's method (8). Electrophoresis was carried out at 60 V for 60 min in 50 mM Tris-glycine buffer (pH 8.4) in 0.1% SDS on 4-40% SDS polyacrylamide micro-disc gels (9). The gels were stained with Schiff's reagent (PAS) and Coomassie Brilliant blue R-250 (C.B.) and then s...
