CONSUMPTION OF EXCESS VITAMIN-A, BUT NOT EXCESS BETA-CAROTENE, CAUSESACCUMULATION OF RETINOL THAT EXCEEDS THE BINDING-CAPACITY OF CELLULARRETINOL-BINDING PROTEIN, TYPE-II IN RAT INTESTINE

We assessed the effects of excess dietary vitamin A or beta-carotene o n the cellular retinol-binding protein, type II [CRBP(II)I level and a ctivities of lecithin: retinol acyltransferase (LRAT) and acyl-CoA:ret inol acyltransferase (ARAT) in rat intestine. Male rats were fed for 7 d diets containing amounts of retinyl acetate or beta-carotene that w ere 1 (control), 10, 100 and 1000 times the NRC recommended requiremen t. No responses of the jejunal CRBP(II) level to an intake of excess v itamin A or beta-carotene were observed. The unesterified retinol and retinyl palmitate concentrations in the jejunum were small in rats fed 10 times the vitamin A requirement but they were significantly greate r in rats fed 100 and 1000 times the vitamin A requirement than in con trols. The molar ratio of unesterified retinol/CRBP(II) was <1 for the controls and the group fed 10 times the vitamin A requirement, but >3 for the group fed 100 times the requirement and >19 for the group fed 1000 times the requirement. The LRAT activity was significantly great er in rats fed 1000 times the vitamin A requirement compared with all other groups, but ARAT activity was unaffected. Consumption of excess beta-carotene did not alter LRAT or ARAT activity, and led to a very s mall deposition of unesterified retinol and retinyl palmitate in the j ejunum. Because CRBP(II) may play an important role in preventing the toxic effect of unbound retinol in the small intestine, consumption of excess vitamin A in amounts <10 times the NRC recommended requirement may not cause a disturbance of the absorptive cell function. In contr ast, consumption of 1000 times beta-carotene requirement may not excee d the binding capacity of CRBP(II) for unesterified retinol in the sma ll intestine.