| Abstract: | The effects of vasoactive intestinal polypeptide (VIP) on exocrine protein secretion were studied in enzymatically dispersed cell aggregates from rat parotid glands. VIP (10(-9) - 10(-7) M) stimulated secretion of alpha-amylase in a dose-dependent manner. The VIP-induced release of alpha-amylase was potentiated in the presence of a phosphodiesterase inhibitor. Basal levels of cyclic AMP of the dispersed cells were increased 6.7-fold after stimulation for 10 min by VIP (10(-7) M). The VIP-induced release of alpha-amylase was reduced by 40% when cells were incubated in a Ca2+-free medium in the presence of ethylene glycol bis(beta-aminoethyl ether)-N,N'-tetraacetic acid (EGTA). Efflux of 45Ca2+ was significantly increased over basal levels by stimulation with VIP (10(-8) and 10(-7) M), but this increased efflux was approximately only half the increased efflux induced by carbachol (10(-5) M). VIP had no effect on the incorporation of 14C]leucine into protein by parotid cells, whereas incorporation was reduced to 30% of the control value by carbachol (10(-5) M). Thus, the VIP-ergic secretory response in the rat parotid gland is associated with a raised intracellular cyclic AMP level and the mobilisation of a different intracellular Ca2+ pool than that mobilised by carbachol. It is, therefore, closely analogous to the beta-adrenergic response. |
