Plasma constituents, endogenous

As an alternate approach to separating these can-nabinoids from endogenous plasma constituents, some bonded phase columns operated in a normal phase mode were investigated. Prior experience in our laboratory (13) had demonstrated the dependability of silica gel when used to process numerous plasma samples. That is, resolution was unaffected by the numerous endogenous plasma constituents continually placed on the column. 

Resolution of A9 -tetrahydrocannabinol from the endogenous plasma constituent. 

Detection of either I or VI in HPLC eluent was found to be practical using UV light at 209 nm. Mobile phases used had to be compatible with monitoring at this wavelength to obtain the sensitivity needed for plasma assays. In the assay for I a 0.3% isopropanol in heptane solution as mobile phase met these criteria as did water acetonitrile in the assay for VI. The assay developed for I required the use of two tandem bonded-phase columns to adequately separate drug and endogenous plasma constituents. 

Plant products have also been detected in non-plant organisms. Morphine 1, the archetypal plant alkaloid, has in fact been shown to be a physiological plasma constituent and its production in mammals could be traced to the liver expression of the critical enzymes of its biosynthesis.17 In addition, the plant hormone abscisic acid 12 has been detected as an endogenous constituent of human brain,18 while caffeine 13 was isolated from a marine gorgonian (Paramuricea chamaelon)19 and the atisane diterpenoid serofendic acid 14, an inhibitor of the oxidant-induced mitochondrial death pathway and putative activator of mitoK(ATP) channels, has been characterised from foetal calf serum.20... 

Cholesterol is a major constituent of the cell membranes of animal cells (see p. 216). It would be possible for the body to provide its full daily cholesterol requirement (ca. 1 g) by synthesizing it itself However, with a mixed diet, only about half of the cholesterol is derived from endogenous biosynthesis, which takes place in the intestine and skin, and mainly in the liver (about 50%). The rest is taken up from food. Most of the cholesterol is incorporated into the lipid layer of plasma membranes, or converted into bile acids (see p. 314). A very small amount of cholesterol is used for biosynthesis of the steroid hormones (see p. 376). In addition, up to 1 g cholesterol per day is released into the bile and thus excreted. 

Cleanup and concentration of corticosteroids from coextracted matrix constituents can also be accomplished using solid-phase extraction cartridges that contain nonpolar Cig (527, 535), or Cg sorbents (452), as shown in Table 29.17. In addition, Cig cartridges have been used to extract endogenous and synthetic corticosteroids from swine plasma (536), and to isolate cortisol from plasma or serum samples (537). Other workers employed conventional columns containing deactivated Florisil to isolate cortisol in milk (529) or fluoroprednisolone in bovine tissues (533). 

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