Protein secretion from rat submandibular acini and granular ducts: Effects of exogenous VIP and substance P during parasympathetic nerve stimulation

The influences of exogenous vasoactive intestinal peptide (VIP) and substance P on the release of peroxidase from acini and true tissue kallikrein (rK1) from granular ducts of the rat submandibular gland were studied during continuous parasympathetic stimulation. Parasympathetic nerve impulses caused a moderate flow of saliva (mean +/- SD, 108 +/- 26 mu l/g tissue/min) that had a low protein concentration (174 +/- 88 mu g/ml). The outputs of peroxidase and rK1 were minimal (14.3 +/- 11.8 pmol DCF/g tissue/min and 6.5 +/- 3.4 nmol AFC/g tissue/min, respectively). When administered intravenously, VIP had no apparent effect on the overall flow rate, but caused a significant increase in the output of peroxidase; 450% at 1 mu g/kg and a further 10-fold increase at 10 mu g/kg. In contrast, substance P (1 mu g/kg) evoked a marked increase in flow rate (68%), and peroxidase secretion increased only 3-fold. The output of rK1 was unaffected by either VIP or substance P. Our results support the hypothesis that acinar, but not granular duct, protein secretion is evoked by non adrenergic, non-cholinergic peptides released from parasympathetic nerve terminals. (C) 1998 Elsevier Science Inc.