It has been assumed that a mononuclear phagocyte system is related to the excretion of PFC emulsions: PFC particles are phagocytized by blood monocytes to be expelled through the lung alveoli. This monocyte-related mechanism may well explain excretion at an early stage when PFC particles are abundant in the blood stream. It does not, however, fully explain the manner by which PFC cells are released from the RES cells into the blood stream and into the adipose tissue. To explain this, the following mechanism has been proposed and discussed based on some experimental results. PFC emulsion particles taken up by the RES organs, are stripped at their surfactant layers in the cells and move across the cell membranes to the blood vessels and into other tissues such as adipose, at a rate that depends on the lipophilicity of the PFC's. In the blood stream, PFCs are delivered by lipoproteins to the lung and excreted into the expired air. Pharmacokinetical analysis with a compartmental model for the excretion also supported this proposed mechanism.
The plasma concentration profile, urinary excretion rate and diuretic response were studied in anaesthetized dogs after an intravenous administration of torasemide or furosemide. The urinary excretion rate of furosemide decreased rapidly after administration. The plasma concentration, which is related to the urinary excretion profile, also decreased rapidly. The diuretic response, which reflected the excretion rate, occurred rapidly after administration but lasted for a short time. The urinary excretion rate of torasemide was much lower than that of furosemide and decreased slowly after administration. The plasma concentration also decreased slowly. The diuretic response to torasemide occurred more slowly but lasted longer than the response to furosemide. These results suggest that the diuretic response profile of either diuretic depends on their urinary excretion rate, and that the difference in the diuretic response between torasemide and furosemide may be explained by the different transfer rate of the drugs from the plasma to the nephron.
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