[Glycerin: utilization, turnover capacity and biokinetic data in intravenous administration in the rat]

During continuous infusions of 24--48 hours, glycerol utilization and turnover capacity in rats were estimated in a range from physiological to toxic doses. Total clearance, elimination constant, half life, transfer and pool size were calculated for various rates of infusion as well as for the endogenous turnover. With increasing blood level, the turnover rate rises like an enzyme saturation curve, first rapidly and then ever more slowly to a maximum value. Therefore, the steady state blood levels do not increase linearly with the infusion rate. The renal excretion of glycerol is below 1 per cent of the supply up to rates of infusion of 0.4g with kg-1 with h-1. Even beyond the upper limit of the metabolic turnover a steady state is reached due to the high renal excretion. Beginning with 2 mumol/ml the excretion rises linearly with the blood level. At rates higher than 0.5g with kg-1 with h-1 the individual differences of the steady state levels are high. A significant negative correlation between the steady state levels of glycerol in blood and the activity of glycerol kinase in the liver and kidneys was observed. Necroses of the renal tubuli were found at infusion rates exceeding the turnover capacity in animals with low enzyme activity. The conclusions which may be drawn from these data regarding the parenteral supply of energy-yielding substrates are discussed.