R C Pittman

On the interpretation of studies measuring uptake and esterification of [1-14C]palmitic acid by rat adipose tissue in vitro

Abstract 1. 1.The effects of glucose and a number of hormones on the incorporation of [1- 14 C]palmitic acid from the medium into glycerides in rat epididymal fat pads have been reported. The data from such studies should not, however, be used to draw conclusions about tha rate of triglyceride synthesis in this tissue. 2. 2. It has been demonstrated that the free fatty acids in different cell fractions and in different parts of a single fat pad have different specific radioactivities after incubation of the intact fat pad in the presence of [1- 14 C]palmitate, suggesting that there are kinetically distinguishable pools of free fatty acids within the tissue. 3. 3. Evidence is presented to support the view that free fatty acids from the medium can, as such, enter adipose tissue cells, and it suggested that there is a pool of free fatty acids, perphaps very small, within the tissue which serves as the precursor pool for glyceride synthesis.

The Role of the Liver in LDL Catabolism

In 1974 we showed that after total hepatectomy both pigs and dogs degrade injected 125I-LDL at a rate equal to or actually greater than the rate in the intact animal (Sniderman et al. 1974). Those results established for the first time the large potential capacity of extrahepatic tissues to degrade LDL in vivo. However, no final quantitative conclusions could be reached regarding the relative roles of liver and extrahepatic tissues in the intact animal because of the possible perturbations accompanying hepatectomy. The very fact that fractional catabolic rate increased after hepatectomy indicated that some acute change induced by the procedure must influence extrahepatic LDL metabolism. A hypothesis that might explain the phenomenon was advanced (Steinberg et al. 1974) but others are possible and the basis for the paradoxical finding remains undefined. Nor did those studies provide any independent assessment of the relative contribution of different extrahepatic tissues to overall LDL degradation.