The peritoneal clearance and peritoneal transfer of oxalic acid, vitamin C, and vitamin B6 in 32 patients during continuous ambulatory peritoneal dialysis (CAPD) using peritoneal dialysis solutions containing 1.5% or 2.5% glucose were examined. The plasma level of oxalic acid was significantly elevated in all patients, plasma vitamin C was in the normal range or in the upper margin of the normal range, and plasma vitamin B6 was in the normal range. The peritoneal clearance of oxalic acid was significantly lower, and the peritoneal clearance of vitamin B6 was the lowest in comparison to the peritoneal clearance of urea. With the exception of vitamin B6, the peritoneal clearance and peritoneal transfer of the examined parameters increased using the dialysis solution containing 2.5% glucose. We found direct relationships between the plasma levels of oxalic acid and creatinine as well as plasma vitamin C and between the peritoneal transfer of oxalic acid and the peritoneal transfer of vitamin C as well as vitamin B6. The significant hyperoxalemia of our patients was found to persist despite the relatively high peritoneal transfer of oxalic acid during CAPD. These results suggest that CAPD is not a method effective enough for permanent reduction of the plasma levels of oxalic acid.

Urinary excretion of vitamin B₆, oxalic acid and vitamin C was investigated in 15 healthy subjects during maximal water diuresis and in the group of 12 patients in polyuric stage of chronic renal failure without dialysis treatment receiving a diet containing high sodium chloride (15g/day). Urinary excretions of the same parameters were investigated in another group of 15 patients in polyuric stage of chronic renal failure without dialysis treatment after i.v. administration of 20 mg furosemide. Urinary excretion of vitamin B₆, oxalic acid and vitamin C significantly increased during maximal water diuresis while during high intake of sodium chloride the urinary excretions of these substances were not affected. The results suggest that urinary excretion of vitamin B₆, oxalic acid and vitamin C depends on the urinary excretion of water. Intravenous administration of 20 mg furosemide led to an increase of urinary excretion of vitamin B₆, oxalic acid and vitamin C in patients with chronic renal failure. The increased urinary excretion of vitamin B₆ and vitamin C is a new negative side effect of furosemide and increased urinary excretion of oxalic acid is a new positive side effect in patients with chronic renal failure.

Vasovagal syncope induced by tilt testing is associated with increased levels of noradrenaline, adrenaline, dopamine and cAMP. These results suggest that sympathoadrenal activation antecedes development of vasovagal syncope and may play a role in its pathophysiology.