Kinetics of Blood‐brain Barrier Transport of Pyruvate, Lactate and Glucose in Suckling, Weanling and Adult Rats

The kinetics of the uptake from blood to brain of pyruvate, lactate and glucose have been determined in rats of different ages. The carotid artery single injection technique was used in animals anaesthetized with pentobarbital. The rates of influx for each substrate were determined over a range of concentrations for the different age‐groups. Data were analysed in terms of the Michaelis‐Menten equation with a component to allow for non‐saturable diffusion. Values are given for K m , V max and K d . In suckling rats (15‐21 days) the V max values for both pyruvate and lactate were 2.0 μmol g −1 min −1 . In 28‐day‐old rats the V max values had fallen to one‐half and in adults they were less than one‐tenth. K m , values were higher in the younger animals. The rate of glucose transport in suckling rats was half that of 28‐day‐old and adults although there was no difference with age in the K m values. The results are discussed in relation to the net flux of these substrates in and out of brain during different stages of post‐natal development.