Objectives: The role of hydrophobicity in the pathophysiology of the gastrointestinal tract is well established as a protective mechanism against the impact of lumenal acid and pepsin. Hydrophobic properties of esophageal secretion in humans remain largely unknown.
Methods: We have studied, therefore, hydrophobicity by using fluorescence probe in human esophageal secretion, elaborated under the impact of saline followed by HCl, HCl/pepsin, and final saline.
Results: Basal hydrophobicity of human esophageal secretion, elaborated during mucosal exposure to saline, was 237 +/- 32. This value, however, declined 72% during mucosal exposure to HCl (66 +/- 14 vs 237 +/- 32; p < 0.001) and 87% during mucosal exposure to acid supplemented with pepsin (30 +/- 4 vs 237 +/- 32; p < 0.001). Moreover, hydrophobicity upon perfusion with HCl/pepsin was 55% lower than after perfusion with HCl alone (30 +/- 4 vs 66 +/- 14), although the result was insignificant. Substitution of saline for HCl/pepsin solution during the last perfusion period resulted in a partial recovery of hydrophobicity in esophageal secretion (131 +/- 30 vs 30 +/- 4; p < 0.001), although this value was lower than the basal hydrophobicity value (131 +/- 30 vs 237 +/- 32; p = 0.028). In addition, we continuously observed a significant shift in the fluorescence emission maximum from 508 +/- 6.4 to 486 +/- 0.9 (p < 0.001) during perfusion with starting saline, to 492 +/- 1.6 (p < 0.001) during exposure to HCl, to 493 +/- 1.1 (p < 0.001) during perfusion with HCl/pepsin, and to 488 +/- 0.9 (p < 0.001) during infusion of final saline. The maximum emission wavelength after esophageal exposure to initial saline also was significantly lower than the maximum emission upon perfusion with HCl (492 +/- 1.6 vs 486 +/- 0.9; p < 0.05) and HCl/pepsin (493 +/- 1.1 vs 486 +/- 0.9; p < 0.05). Although basal hydrophobicity in males was similar to corresponding values recorded in females, mucosal exposure to HCl (pH 2.1) resulted in an 84% decline in females but only 60% in males. Therefore, the hydrophobicity value in females during the perfusion period with HCl was 52% lower than in males (p = 0.129).
Conclusions: Esophageal secretion exhibits its hydrophobic nature presumably through the presence of mucus components such as mucin and mucin-associated phospholipids. The inhibitory impact of HCl and HCl/pepsin solutions on esophageal hydrophobicity may play a role in the pathogenesis of mucosal damage by gastroesophagel refluxate.