Increased levels of substance P in patients taking beta‐blockers are linked with a protective effect on oropharyngeal dysphagia

BACKGROUND: We have recently found a potential protective effect of beta-blockers on oropharyngeal dysphagia (OD). The action mechanism by which beta-blockers could wield this protective effect is unknown, but the neurotransmitter substance P (SP) could play a key role. The aim of this study was to analyze serum and saliva SP levels in patients taking beta-blockers (TBB), and to explore its relationship with OD. METHODS: Adult (>50 year) patients TBB were randomly recruited from the primary care setting and 1:1 matched by age, sex, and Barthel Index (BI) with patients not taking beta-blockers (NTBB). Serum and saliva samples were taken and analyzed for their SP levels using an enzyme-linked immunosorbent assay (ELISA). Socio-demographic and clinical variables were collected. Dysphagia was evaluated in all patients using the clinical volume-viscosity swallow test (V-VST). KEY RESULTS: We studied 28 patients TBB (64.96 ± 7.31 years, 57.1% women, BI 99.6 ± 1.31, carvedilol-equivalent dose 24.11 ± 18.12 mg) and 28 patients NTBB (65.61 ± 6.43 years, 57.1% women, BI 99.6 ± 1.31). SP serum levels were significantly higher in patients TBB (260.68 ± 144.27 vs 175.46 ± 108.36 pg/mL, P = .009) as were SP saliva levels (170.34 ± 146.48 vs 102.73 ± 52.28 pg/mL, P < .001) compared with patients NTBB. The prevalence of OD was 32.1% in patients TBB and 67.9% in patients NTBB (P = .015). Moreover, patients with OD had significantly lower SP saliva levels in comparison with patients without clinical signs of OD (98.39 ± 43.25 vs 174.69 ± 147.21 pg/mL) P < .001. CONCLUSIONS & INFERENCES: We have found that serum and saliva SP levels are greater in patients TBB. This increase in SP levels could be the action mechanism by which beta-blockers protect patients from OD.