Abstract
Very low density lipoprotein (VLDL) is a major transport vehicle of triglycerides (TG) of endogenous organ in plasma. A major factor determining the amount of TG secreted in VLDL is an availability of free fatty acid (FFA) of either exogenous or endogenous origin. From a practical standpoint, a release of VLDL-TG from liver was associated with a level of plasma FFA concentration, and a hydrolysis of VLDL-TG might be dependent on an energic source in human metabolism. It is possible, therefore, that a VLDL-TG play a role on an initiative factor in lipoprotein metabolism. On the other hand, experimental studies using glucose, noradrenaline, and nicotinate in the rabbits showed as follows: 1) Plasma FFA concentration in the rabbits treated with glucose or nicotinate was significantly decreased, while that in the rabbits with noradrenaline was markedly increased as compared with that in the rabbits with saline. 2) Radioactive plasma FFA and VLDL-TG after the infusion of 14C-palmitate were the highest values in the noradrenaline group, but those were the lowest values in the nicotinate group as compared with those in each group. Under the condition loaded with glucose, a significant change in radioactive plasma FFA was not observed, but the radioactive VLDL-TG was increased as compared with that in the control. Additionally, half life of the both plasma FFA and VLDL-TG were more prolonged than those in the other 2 groups. 3) Radioactive TG in adipose tissue was markedly increased by the glucose, while those in the both groups treated with noradrenaline or nicotinate were decreased. These results suggests that a synthesis or a hydrolysis of VLDL-TG is regulated by an energy metabolism. Under the condition utilized FFA as an energic source, VLDL-TG synthesis is apparently accerelated, but it is result from the increased plasma FFA releasing from the adipose tissue. It is possible, therefore, that a release or a synthesis of VLDL-TG is controled by the homeostatic balance which is dependent on a certain level of plasma FFA concentration. Under the condition utilized glucose, plasma FFA is availabled for a VLDL-TG synthesis or an accumulation of TG in adipose tissue. However, VLDL-TG hydrolysis is reduced, and an abnormal lipoprotein metabolism of VLDL to low dencity lipoprotein can be observed at this condition.
