Movement of lipids into and out of the blood during hyperlipidemia induced in rabbits by pituitary extract and fraction H.

Rabbits were rendered hyperlipidemic by the subcutaneous injection of an alkaline aqueous extract of mammalian pituitary gland or a partially purified, concentrated fraction derived therefrom, designated Fraction H. Eight hours after the injection of Fraction H, arteriovenous (A-V) differences in plasma triglyceride (TG) were measured across five body areas. A large negative A-V difference in plasma TG was consistently found across the liver (increase in plasma concentration), and a moderate positive A-V difference across the perirenal fat depot (decrease in plasma concentration). Most values obtained across the intestines and mesentery and the leg were positive. Differences across the kidney were mostly small and almost equally divided between positive and negative values. Similar results were obtained 7-12 and 16-18 hr after injection of the pituitary extract. It is concluded that the liver is the principal source of the TG for this kind of hyperlipidemia, and that the plasma TG levels are reduced principally in passage through adipose tissue. A consistent negative A-V difference in plasma free fatty acid concentration (net increase) was found across the kidney 7-12 hr after injection, suggesting that the kidney hydrolyzes its accumulated TG and mobilizes it in the form of free fatty acids.