Feeding behavior of lambs in relation to kinetics of 1,8-cineole dosed intravenously or into the rumen.

The monoterpene 1,8-cineole is a major constituent of the essential oils that adversely influence intake of sage brush by herbivores, but little is known about the mechanisms of its action. We investigated the influence of 1,8-cineole on the feeding behavior of two groups of sheep, one group dosed intravenously and the other intra-ruminally. In the first study, we infused 40 mg/kg BW of 1,8-cineole intravenously into four lambs on wk 1, 2, and 4. In the second, we administered 125 mg/kg BW of 1,8-cineole into the rumen of four lambs as a single-bolus dose in wk 1 and 2. Lambs dosed intravenously spent less time feeding than controls (28 vs. 60 min; P<0.05), as did lambs dosed intra-ruminally (35 vs. 60 min; P<0.05). Dosed lambs ate less than controls during rumen dosing studies (P<0.05). For the intravenous infusion studies, rates of elimination did not differ among weeks (P<0.05). For the rumen infusion studies, however, the absorption rate constant increased from 0.035/min to 0.076/min from wk 1 to 2, while the absorption half-life declined from 24 to 10 min (P<0.05). Maximum plasma concentrations and time to reach maximum plasma concentrations were no faster in wk 2 than wk 1, but the primary elimination rate constant was 2.3 times higher in wk 2 (0.058/min) than in wk 1 (0.025/min) (P<0.05). Dosed lambs exhibited clinical effects-licking of lips, drowsiness, staggering, and 1,8-cineole-smelling breath-that were much more pronounced with intravenous than rumen infusions. Dosing did not affect the acid-base balance. Collectively, these data suggest 1) rapid absorption and distribution of 1,8-cineole was responsible for initiating satiety, while more prolonged excretion was responsible for the duration of the satiety effect, and 2) lambs more readily adapted to 1,8-cineole in the rumen-dose study than in the intravenous-dose study.