Factors Which Affect Cerebral Uptake and Retention of exp 13 NH sub 3

摘要

The single pass extraction of ammonia (E) by cerebral capillaries was studied in vivo in Rhesus monkeys with exp 13 N. The value of E for exp 13 N-ammonia was found to be less than 100%, inversely related to cerebral blood flow and to be limited by the permeability of the blood brain barrier for ammonia. A vaue of the permeability surface area product was determined to be 0.0040 x 10 exp -4 cm exp 3 /sec/gm. The single pass extraction fraction, E, for exp 13 N-ammonia was found to be independent of arterial blood pH (in the range of 7.2 to 7.6) and of arterial blood ammonia concentration (in the range of 80-1400 mu gms/100 cc). An insulin induced hypoglycemic reduction in the cerebral metabolic rate for glucose and oxygen of 54% produced a reduction in E of about 24%. When a condition of elevated arterial blood ammonia was added to hypoglycemia, the value of E and cerebral metabolic rate for oxygen remained low while the cerebral metabolic rate for glucose increased by a factor of 2.5 indicating the presence of a detoxification shunt for ammonia. Positron tomographic images of the equilibrium cross section distribution of exp 13 N-ammonia appeared to reflect regional differences in capillary density of the cerebral tissue. (ERA citation 02:038434)