Figure 1.

Urinary levels of hydroxyvanillic acid ((A); HVA), 5-hydroxyindoleacetic acid ((B); 5-HIAA), hydroxyvanilic acid/5-hydroxyindoleacetic acid ratio ((C); HVA/HIIA),p- hydroxyphenyl acetic acid ((D); PhAc) and 3-indoxyl sulfate ((E); 3-IS) expressed in milligrams per gram of creatinine (mg/gCr) in the control group (green) and patients with functional constipation (blue). Data are presented as Mean; error bars represent SD values. Differences between controls and patients were evaluated by the Student’s or the Mann–Whitney U test; *** p < 0.001; average ± SD; Student’s t-test assessed differences between groups.