Intestinal absorption of the intact peptide carnosine in man, and comparison with intestinal permeability to lactulose.

1. Healthy humans ingested the dipeptide carnosine (L-beta-alanyl-L-histidine). Their plasma levels and urinary outputs of carnosine and beta-alanine were monitored over the following 5 h. 2. Large amounts of intact carnosine (up to 14% of the ingested dose) were recovered in the urine over the 5 h after ingestion. However, carnosine was undetectable in the plasma unless precautions were taken to inhibit blood carnosinase activity ex vivo during and after blood collection. 3. The amount of carnosine recovered in urine varied substantially between subjects. It correlated negatively with carnosinase enzymic activity in the plasma. Highest carnosinase activities were observed in those subjects who regularly underwent physical training. 4. Urinary recovery of the disaccharide lactulose also varied considerably between subjects, but was substantially lower than that of carnosine. There was no significant correlation between the recoveries of carnosine and lactulose. 5. When lactulose was ingested with a hypertonic solution, the urinary recovery of lactulose was generally increased. When carnosine was ingested with a hypertonic solution, the urinary recovery of carnosine was reduced: hence the paracellular route probably is not dominant for absorption of intact carnosine. 6. Intact carnosine must have crossed the intestine to an extent much greater than hitherto recognized. Rapid post-absorptive hydrolysis is a severe obstacle to quantification of intact peptide absorption.

Changing effects on erythrocyte sodium and potassium during the development of chronic renal failure with anaemia in rats.

Rats were studied 7 days and 17 days after the onset of renal failure which was induced by a surgical technique. Plasma urea, creatinine (PCr) and potassium had increased after 7 days; plasma potassium increased much more after 17 days but PCr was slightly lower. Renal failure caused resetting of erythropoietic control to a lower level of packed cell volume (PCV). After 7 days renal failure some rats had a low PCV, whereas others still had a normal PCV apparently due to slower erythrocyte destruction of pre-renal failure cells. After 7 days renal failure, rats with a normal PCV had an increased erythrocyte membrane leak to potassium that resulted in a low erythrocyte potassium [K+]RBC. This was accompanied by an increase in active sodium pump units [increased ouabain sensitive sodium flux (Fo) and its rate constant (ko)] that caused erythrocyte sodium ([Na+]RBC) to fall. The increased active pump units retarded the fall in [K+]RBC and may have extended the life of the normal erythrocytes in the renal failure environment. The PCV was below normal in all rats after 17 days renal failure. [K+]RBC was increased and since ko was normal there appeared to be compensation to produce erythrocytes with reduced membrane leak to potassium with longer standing renal failure. PCr was only related to PCV after 17 days renal failure and not in the earlier phase of erythrocyte destruction. The changes in erythrocyte membrane permeability were very significantly related to PCV after 17 days.