Kinetics of chylomicron triglyceride removal from plasma in rats: a comparison of the anesthetized and the unanesthetized states.

The kinetics of chylomicron-TG removal were studied using an experimental method which allows measurements to be made under optimal physiological conditions. Chylomicrons, labeled with palmitic acid-(14)C, were constantly infused at a rate of 0.5 mg total lipid per min into chronically cannulated, unanesthetized, unrestrained rats which had been fasted for 18 hr. Serial blood samples were withdrawn from an arterial cannula during a 20 min infusion period and for 10 min following the infusion. Plasma lipoproteins were separated into two fractions in the ultracentrifuge, and the lipids were extracted. Radioactivity in the low-density fraction (d<1.006) was taken to represent chylomicron-TG radioactivity. Using this method we studied the influence of anesthesia on the kinetics of removal of chylomicron-TG. The following three phases of the radioactivity-time curve were plotted: (a) the increase in (14)C during infusion of chylomicrons, (b) the steady-state phase during the infusion, and (c) the decay of (14)C after chylomicron infusion was stopped. The values for the anesthetized rats failed to reach a steady-state phase during the course of the experiment. From the disappearance of (14)C following the end of the infusion, the apparent half time of removal of chylomicron-TG was estimated to be 2.8 +/- 0.37 min in unanesthetized rats, 4.5 +/- 0.37 min in rats anesthetized with sodium pentobarbital, and 4.4 +/- 0.44 min in rats anesthetized with halothane. Thus, two anesthetics with different physical properties markedly slowed the removal of chylomicron-TG from the circulation. The reduced rate may have resulted from alterations in cardiac output or distribution of blood flow induced by the anesthetic agents.