Objectives: To investigate the changes in the muscarinic receptor signaling pathway with submandibular gland (SMG) transplantation and whether carbachol improves secretion in transplanted SMGs.
Materials and methods: SMG autotransplantation was performed in a rabbit model. Carbachol (1 microM) was infused into the transplanted glands from postoperative day 1-7. The expression of the M1 and M3 muscarinic receptors, aquaporin-5 (AQP5), and phosphorylated extracellular signal-regulated kinase 1/2 (p-ERK1/2) was measured by RT-PCR, immunoblotting or immunofluorescence. The content of inositol 1, 4, 5-trisphosphate (IP(3)) was measured by radioimmunoassay.
Results: Salivary flow of the transplanted SMGs was decreased after transplantation. As well, the expressions of M1 and M3 receptors and their downstream signaling molecules, IP(3), p-ERK1/2 and AQP5, were all reduced. Atrophy of acinar cells was shown in transplanted glands. However, all these alterations were reversed after carbachol treatment for 7 days. Furthermore, carbachol directly increased the mRNA expression of AQP5 and phosphorylation of ERK1/2 in cultured neonatal rabbit SMG cells.
Conclusion: A lack of acetylcholine and downregulation of the muscarinic receptor signaling pathway is involved in the early hypofunction of transplanted SMGs. Carbachol treatment could be a new therapeutic strategy to improve secretion and prevent the obstruction of Wharton's duct in the early phase after SMG transplantation.