Effect of vitamin C on urine pH in cats

The effect of single oral doses of crystalline ascorbic acid (100 or 1000 m g/kg body weight (BW) added to a vitamin C-free basal diet based on poultry meal) or polyphosphated ascorbic acid (100 mg/kg BW) on plasma ascorbic ac id levels and excretion into the urine were investigated in six adult Europ ean shorthaired cats. Plasma iea els of ascorbic acid increased significant ly after feeding. The maximum was reached about 4h postprandially, whereas in the vitamin C-free control diet there was no difference between values b efore and after feeding (controls: 4.5+/-3.9 mu g/ml; dose of 100 mg/kg BW: 11.9 +/- 3.4 mu g/ml; dose of 1000 mg/kg BW: 37.8 +/- 10.7 mu g/ml). After the single dose of 100 mg/kg BW renal excretion of ascorbic acid amounted to 5.9 +/- 3.6 mg/kg BW, after the intake of 1000 mg/kg BW 45 +/- 32 mg/kg BW were excreted via the kidney. There were no differences between single d oses of polyphosphated and crystalline ascorbic acid. In the second part of the experiment the effect of ascorbic acid on urine pH was tested with two diets: increasing doses of ascorbic acid were added for several consecutiv e days either to the basal diet (200, 400, 600, 800 and 1000 mg/kg BW per d ay) or to minced beef (200, 400, 1000 mg/kg BW per day). In the basal diet there were no chan; of urine pH up to a dose of ascorbic acid of 800 mg/kg BW. When 1000 mg/kg BW were given the urine pH decreased significantly to 6 .85 +/- 0.24 (control without ascorbic acid: 7.12 +/- 0.22). In contrast to that in the minced beef diet, the effect of ascorbic acid on urine pH occu rred already at much lower doses and was much more marked at the highest do se (control: 6.93 +/- 0.54, 200 mg/kg BW: 6.77 +/- 0.51, 400 mg/kg BW 6.62 +/- 0.41, 1000 mg/kg BW 6.47 +/- 0.39). ascorbic acid led to a dose-depende nt decrease of faecal pH and dry matter.