p-Cresol is a metabolite of aromatic amino acid metabolism produced by intestinal microflora, and its formation is influenced by intestinal conditions. Fasting drastically changes intestinal conditions. However, the effect of fasting on
p-cresol production is unclear. In this study, serum and cecal
p-cresol levels were determined in non-fasted rats and in rats fasting for either 12 or 18 h. Serum
p-cresol increased significantly with 12-h fasting (3.44 ± 2.15 nmol/ml;
P<0.05) and 18-h fasting (5.40 ± 2.20;
P<0.001) as compared to the level in the non-fasted rats (1.02 ± 0.50). Cecal
p-cresol levels of the 12-h fasted (272.6 ± 313.2 nmol/cecum) and 18-h fasted rats (436.6 ± 190.8;
P<0.01) were higher than those in non-fasted rats (27.1 ± 21.9). The total cecal protein in content did not change with 18-h fasting. However, the cecal protein concentration increased significantly with fasting (
P<0.001), and correlated closely with total cecal
p-cresol contents (
P<0.001). These results indicate that fasting enhances
p-cresol production in the rat cecum, resulting in accumulation of serum
p-cresol. We presume that the increase in
p-cresol produced by fasting is related to the enhancement of bacterial nitrogen metabolism via an increased concentration of endogenous protein in the cecum.
View full abstract