Effects of indole alkaloids and related compounds on the properties of brain microtubular protein.

In contrast with results on the rat, in the rabbit no arteriovenous differences were found in the plasma concentrations of free choline, phosphatidylcholine and lysophosphatidylcholine. The phospholipid values agreed with those of Nelson (1967). Blood samples were taken at intervals and the blood volume was replaced by infusing a dextran solution in which blood cells from earlier samplings were suspended. After this procedure, however, it was observed that the concentration of free choline in the plasma rose. This may be related to the transfusion of separated cells suspended in dextran. The concentration of the two choline glycerophospholipids fell owing in part to the plasma dilution with dextran, although the percentage of lysophosphatidylcholine rose from 17.6 to 26.0% of the total phospholipids. An infusion of choline (lpmol/min per kg body weight) caused a considerable rise in the free choline concentration of plasma followed by a fall to the ‘dextran-stimulated’ level. A second choline infusion again caused a rise in the free choline concentration. Infusion of choline failed to prevent the gradual decline in lipid choline concentrations. Thus although the rat showed marked differences in the free choline concentration of jugular vein compared with the femoral artery, this could not be detected in the rabbit. In the rabbit, choline infusion raised the concentration of free choline but failed to prevent the fall in the concentration of plasma choline glycerophospholipids.