Introduction Human saliva has a high nitrite concentration from the entero-salivary recirculation of dietary nitrate. Swallowed nitrite reacts with acidic gastric juice forming nitric oxide (NO). Increasing NO bioactivity, by inhibiting phosphodiesterase, enhances gastric accommodation and delays gastric emptying.
Aims To determine (1) whether nitrite in saliva affects gastric emptying and (2) whether nitrite in saliva alters postprandial intragastric pressure (IGP).
Methods 20 healthy subjects (11 males) were studied. On four separate days high-resolution manometry was performed during 15 min fasting and for 90 min following a standardised meal. Post-prandially, solutions of 0, 0.286, 2 and 14 mmol/l potassium nitrite were infused into the oral cavity. Solutions were randomised and double-blinded. Saliva was collected at baseline, 30, 60 and 90 min after the meal. Salivary nitrite concentrations were quantified by Griess reaction. Gastric emptying was assessed by means of a specially designed breath test. 14C labelled sodium acetate was incorporated, during baking, into a rolled oats flapjack which constituted part of our standardised meal. Following consumption of the flapjack, breath samples were taken at regular intervals. The quantity of 14C appearing in breath per unit time (μmol/minute) was calculated. A generalised linear regression method was used to estimate gastric half-emptying times (T½). Mean IGP was defined relative to atmospheric pressure as the lowest mean pressure recorded in the six most distal manometry sensors. Results are medians and ranges.
Results Salivary nitrite concentrations at 60 min were 24.35 μmol/l (3.86–65.46), 80.42 μmol/l (20.88–158.79), 358.4 μmol/l (118.2–726.6) and 2694 μmol/l (600–8087) for the solutions containing 0, 0.286, 2 and 14 mmol/l nitrite, respectively. There was no significant difference in the rate of gastric emptying (T½) between the control solution (103.5 min, 56.2–239.1) and those containing 0.286 mmol/l (113.4 mins, 68.7–254.8, p=0.56), 2 mmol/l (121.7 min, 39.8–270.0, p=0.93) and 14 mmol/l (114.4 mins, 79.1–390.1, p=0.75). There was no difference in the increase in IGP recorded between the control solution (4.06 mm Hg, −2.64–7.31) and those containing 0.286 mmol/l (4.42 mm Hg, −4.55–8.45, p=0.61), 2 mmol/l (4.66 mm Hg, −0.94-9.16, p=0.27) and 14 mmol/l (4.24 mm Hg, −2.12–8.17, p=0.81) potassium nitrite.
Conclusion Despite an excellent range of salivary nitrite concentrations, extending over and beyond the normal physiological range, no difference in the rate of gastric emptying or postprandial rise in IGP was seen. This suggests salivary nitrite does not affect gastric emptying.
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