Stimulation of Platelet-activating Factor Synthesis by Neurotransmitters in Salivary Glands

Abstract

Platelet-activating factor (PAF), a phospholipid mediator exhibiting potent biological activities, has been shown to stimulate amylase release from the pancreas and salivary glands. The capacity of salivary glands for PAF biosynthesis in response to stimulation has also been demonstrated. To elucidate the role of PAF in salivary glands, we studied the regulation of platelet-activating factor synthesis by the autonomic nervous system in canine salivary glands. Acetylcholine and ionomycin stimulated PAF production in dispersed cells from parotid, submandibular, and sublingual glands of dogs. Norepinephrine and phenylephrine, but not isoproterenol, also stimulated PAF production in submandibular gland cells. Norepinephrine-induced PAF production was blocked by phentolamine but not by propranolol. Acetylcholine and norepinephrine increased both the PAF production and liberation of [14C]arachidonic acid from cells pre-labeled with [14C]arachidonic acid in the presence of Ca2+ in the medium. These stimulants increased [14C]arachidonic acid liberation without the accompanying production of PAF in Ca(2+)-deprived medium. No activators or inhibitors of protein kinase C produced or affected acetylcholine-induced PAF production. Lyso-PAF:acetyl-CoA acetyltransferase was activated in the cells treated with acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP. Deprivation of Ca2+ in the medium markedly reduced acetylcholine-induced activation of the transferase, but little affected norepinephrine-, isoproterenol-, and 8Br-cyclic AMP-induced activation. Dithiothreitol-insensitive cholinephosphotransferase activity was also increased by acetylcholine, norepinephrine, isoproterenol, and 8Br-cyclic AMP, and the deprivation of Ca2+ in the medium further increased the activation of the enzyme activity by these agents. These results suggest that PAF synthesis in canine salivary glands is under the control of muscarinic cholinergic and alpha-adrenergic systems via Ca(2+)-dependent remodeling pathways, and that the independent activation of either phospholipase A2 or acetyltransferase is insufficient for PAF production in submandibular gland cells, i.e., the concurrent activation of these enzymes is required.

Selenium Modulates 1-O-Alkyl-2-Acetyl-sn-Glycero-3-Phosphocholine (PAF) Biosynthesis in Bovine Aortic Endothelial Cells

“…Together these results suggest that Se deficiency enhances PAF biosynthesis by increasing the activity of anabolic enzymes required for PAF synthesis in the remodeling pathway without affecting the degradation of newly formed PAF. These findings are important because previous research has shown that the concurrent activation of both anabolic enzymes is required for PAF synthesis (6).…”

PAF, a Putative Mediator of Oral Inflammation

“…More recent studies have confirmed and extended these observations, i.e., dispersed, stimulated cells from isolated canine salivary glands produce PAF (Dohi et al, 1991(Dohi et al, , 1996(Dohi et al, , 1997. Both acetylcholine and ionomycin initiate PAF production in cells from parotid, submandibular, and sublingual glands; norepinephrine and phenylephrine stimulate PAF production in submandibular glands.…”