BETA-CAROTENE 15,15'-DIOXYGENASE ACTIVITY AND CELLULAR RETINOL-BINDING PROTEIN TYPE-II LEVEL ARE ENHANCED BY DIETARY UNSATURATED TRIACYLGLYCEROLS IN RAT INTESTINES

The purpose of this study was to examine effects of dietary triacylgly cerols on beta-carotene 15,15'-dioxygenase (EC 1.13.11.21) activity an d cellular retinol-binding protein [CRBP (II)] in rats. Six groups of eight rats (7-wk old) were fed one of the following diets: standard (S TD; 2.5% soybean oil), saturated (SFA; 15% hydrogenated soybean oil), monounsaturated (MUFA; 15% olive oil), polyunsaturated (PUFA; 15% soyb ean oil) or clofibrate (CLF; 2.5% soybean oil + 0.2% clofibrate) for 3 wk. The dioxygenase specific activities of the intestinal homogenates in the MUFA and PUFA groups fed the high fat diets were 2.4 times tha t of the STD group fed a law fat diet (P < 0.01), whereas the activiti es of the SFA and CLF groups were not significantly different from tha t of the STD group. The level of CRBP (II) in the intestine of the PUF A group was 1.3-fold that of the STD group (P < 0.05), whereas there w ere no significant differences among the other groups. In a second exp eriment, the dioxygenase activity of rat intestine was followed over 3 wk of feeding the STD and PUFA diets. After the PUFA diet was consume d for 1 d, the activity was enhanced to 2.7 times the baseline level a nd remained thereafter at that high level, whereas the activity of the STD group remained at the low baseline level. Thus, dietary polyunsat urated triacylglycerols enhanced both beta-carotene 15,15'-dioxygenase activity and CRBP (II) level in rat intestine. These results suggest that the dioxygenase and CRBP (II) are regulated by the same mechanism involving long-chain fatty acids and their metabolites.