Reduced muscarinic parotid secretion is underlain by impaired NO signaling in diabetic rabbits

Abstract

ObjectivesThe influence of experimental diabetes (alloxan, 100mgkg(-1)) was studied on rabbit parotid gland function. Material and MethodsCarbachol-induced parotid secretion in vivo, and in vitro quantification of inducible nitric oxide synthase (iNOS) mRNA expression, by real-time RT-PCR, and activity of superoxide dismutase (SOD) and total antioxidant capacity (TAC) in commercial colorimetric assays were measured in parotid glands of non-diabetic and diabetic rabbits. ResultsCarbachol-induced dose-dependent increase in parotid secretion significantly reduced in diabetic rabbits. Functional studies in the presence of muscarinic receptor and nitric oxide synthase (NOS) antagonists revealed that in M-3 receptor-mediated carbachol secretion, nitric oxide, deriving mainly from neuronal NOS (nNOS) in control, and iNOS in diabetic rabbits, was involved. Also, upregulation of iNOS mRNA expression and enhanced SOD activity and TAC were detected in diabetic glands. ConclusionsOur data suggest that decreased M-3 receptor-mediated parotid secretion in diabetic rabbits appears to be due to alterations in NO signaling, mainly due to iNOS induction, accompanied by elevated antioxidant response.