Blood ammonia concentration in mice: normal reference values and changes during growth.

To establish normal reference values of blood ammonia concentration in mice, possible factors which may affect blood ammonia determination such as age, sex, strain and sampling site of blood, were investigated by the microdiffusion method. The ammonia concentration in blood collected from the tail (mixture of venous and arterial blood) and left ventricle was significantly higher than that in venous blood collected from the orbital sinus and right auricle. Neither strain nor sex differences were observed. Blood ammonia concentration in newborn pups was 92 +/- 19 micrograms/dl immediately after birth and increased to 184 +/- 22 micrograms/dl 24 hours after birth. This increased level was maintained for a week. By 15 days, it decreased to the level at birth. Thereafter, no significant variation with age was observed. Blood ammonia concentration in mice after weaning, irrespective of age, sex and strain, varied from 38 to 123 micrograms/dl, with a mean +/- SD of 79 +/- 18 micrograms/dl.