Squalene in Human and Rat Blood Plasma*

Squalene is a triterpenoid hydrocarbon that was first isolated from shark liver oil and was named by Tsujimoto in 1916 (1).More recently this compound has been found to be widely distributed in biological materials.Squalene has been identi- fied and studied in-plant oils and leaves (2, 3), in fungi (4), in tobacco and cigarette smoke (5), and in fish oils (6, 7).A small concentration of squalene with a rapid turnover has been identi- fied in rat liver (8).Larger concentrations have been found in human sebum-like materials, including sebum (9-12), ear wax (9, 11), hair fat (13), smegma (9), dermoid cyst fat (11, 14), and vernix caseosa (15).Squalene is now well established as the biosyn- thetic intermediate immediately preceding the for- mation of the sterol nucleus.During the course of sterol biosynthesis squalene undergoes direct cyclization to lanosterol, which is then converted to cholesterol (16)(17)(18)(19)(20). Recent studies have also defined the reaction sequence between mevalonic acid and squalene (21-23) and have partly defined the unusual reaction mechanism involved in squalene biosynthesis from its immediate precur- sor, farnesyl pyrophosphate (24-26).The position of squalene in the biosynthetic pathway to cholesterol is indicated in Figure 1.In the present study, small concentrations of metabolically active squalene have been identified in human and rat blood plasma. MethodsForty microcuries of DL-2-C"-mevalonic acid, in solu- tion in isotonic saline, was injected intravenously into a fasting normal young adult man.Serial blood samples were collected in syringes moistened with a solution of *