Calcium, phosphorus, and fatty acids in plasma stored at room temperature

Comparative in vivo and in vitro studies of phenytoin protein binding and in vitro lipolysis in plasma of pregnant and nonpregnant rats

This investigation was designed to determine the cause of the changes in drug protein binding that occur in rat plasma, particularly in plasma from pregnant animals, during in vitro drug-protein binding measurements. In vivo estimates of phenytoin binding in plasma were obtained from steady-state CSF-plasma concentration ratios in pregnant and nonpregnant rats. Immediate ultrafiltration of heparin- or EDTA-anticoagulated plasma yielded phenytoin free fraction values that were in good agreement with in vivo estimates for nonpregnant rats but that were about one-third higher than in vivo estimates for pregnant animals. In vitro free fraction values tended to increase during incubation of plasma and/or during equilibrium dialysis. The concentrations of the four major endogenous free fatty acids were similar in plasma of pregnant and nonpregnant rats if determined immediately after blood collection. Six hours of incubation at 37 degrees C caused fatty acid concentrations to increase about fivefold and twofold in heparin-anticoagulated plasma from pregnant and nonpregnant animals, respectively. The corresponding increases in EDTA-anticoagulated plasma were only about twofold and 1.14-fold, respectively. These changes were associated with decreased plasma protein binding of phenytoin. The in vivo differences between pregnant and nonpregnant rats with respect to phenytoin binding in plasma are not due to differences in fatty acid concentrations, but the in vitro differences are due primarily to corresponding differences in free fatty acid concentrations if extensive in vitro lipolysis occurs.

Biochemical changes induced in human plasma by its lipoprotein lipase

1. Incubation of human citrated plasma with a concentrate of lipoprotein lipase (separated from the same plasma pool), for 6 hr at 37 degree C and pH 7.0, caused a marked decrease in the concentrations of calcium, triglycerides, total phosphorus, lipid phosphorus and total fatty acids. 2. There was a concomitant increase in the concentrations of non-esterified fatty acids and inorganic phosphorus which were presumably formed by enzymatic hydrolysis of triglycerides and lipid phosphorus. 3. These changes in human plasma, induced by its lipoprotein lipase, were quantitatively comparable to the same changes which have been previously reported in liquid plasma between the 1st and 2nd months of storage at room temperature.

Observations on the collection and handling of blood samples for N.E.F.A. estimation

The effect upon the results of estimating plasma or serum non-esterified fatty acids (N.E.F.A.) assay by different methods of collecting blood samples and subsequent differences in sample storage and time of assay have been studied. Standardization of technique is advised and the use of chilled heparinized tubes, with separation of the sample within one hour of collection and assay on the day of collection is advocated.