Measurement of monoterpenes and sesquiterpenes in serum, plasma, and rumen fluid from sheep

Studies involving the consumption, metabolism, and elimination of terpenes by small ruminants consuming terpene-laden shrubs as well as those exploring the potential for natural products as rumen modifiers could benefit from a procedure that measures terpenes in both blood and rumen fluid and that is suitable for either serum or plasma. The objective of this study was to modify an existing procedure for plasma utilizing solid phase extraction/gas chromatography, and extend its use for measurement of structurally diverse mono- and sesquiterpenes in three fluids (serum, plasma, and rumen fluid) from sheep. Generally, terpene recovery was lower from rumen fluid than from serum or plasma, although the extent and direction of differences varied among chemicals. Fourteen terpenes (camphene, β-pinene, α-terpinene, p-cymene, cis-β-ocimene, 1,8-cineole, γ-terpinene, terpinolene, linalool, camphor, longifolene, β-caryophyllene, α-humulene, and caryophyllene oxide) were recovered from serum at near unity. Recovery from rumen fluid was lower than that for serum or plasma for most terpenes, but eight (p-cymene, 1,8-cineole, cis-sabinene hydrate, terpinolene, borneol, terpin-4-ol, α-terpineol, and caryophyllene oxide) were recovered at near unity. Yet, 15 terpene recoveries were below 0.75 ng/ng (tricyclene, α-pinene, camphene, sabinene, β-pinene, myrcene, 2-carene, 3-carene, α-terpinene, cis-β-ocimene, limonene, γ-terpinene, longifolene, β-caryophyllene, and α-humulene). Oxygenated monoterpenes were typically recovered in greater quantities and hydrocarbon monoterpenes were least effectively recovered with this method. This procedure allows for simultaneous measurement and recovery adjustment of a number of terpenes from serum, plasma, and rumen fluid of sheep.