β-Carotene is incorporated or mobilized along with triglycerides in bovine adipose tissue in response to insulin or epinephrine

Pasture fed cattle ingest substantial amounts of beta-carotene (beta-C). Not all of the carotenoid compound is transformed into vitamin A, but the surplus is deposited in adipose tissue (AT). The mechanisms of beta-C incorporation and mobilization are unknown. Two experiments were conducted using explants from bovine AT cultured in vitro. First, beta-C incorporation by explants from three animals was examined with different beta-C concentrations (0, 1, 5 and 20 mu m) and different times of incubation (every 5 h up to 25 h). The data showed a significant increase of beta-C concentration in explants only for 20 mu m beta-C. Secondly, effects of insulin and epinephrine on beta-C and triglyceride (TG) contents of explants were studied. Explants from six animals were incubated with either hormone and 0 or 20 mu m beta-C for 20 h. Both TG and beta-C contents were affected positively by insulin and negatively by epinephrine. Interestingly, changes in ratios of beta-C/TG (hormone vs. control) were similar (1.7 x 10(-3) and 1.8 x 10(-3)), respectively, for insulin and epinephrine, indicating that beta-C level is directly related to TG content. We also report the presence of mRNA for beta-C 15, 15' oxygenase in bovine AT. The in vitro culture system using explants from bovine AT is a promising model to investigate factors that might affect the accumulation and metabolism of beta-C.