Consumption of excess vitamin A, but not excess beta-carotene, causes accumulation of retinol that exceeds the binding capacity of cellular retinol-binding protein, type II in rat intestine.

We assessed the effects of excess dietary vitamin A or beta-carotene on the cellular retinol-binding protein, type II [CRBP(II)] level and activities of lecithin: retinol acyltransferase (LRAT) and acyl-CoA:retinol acyltransferase (ARAT) in rat intestine. Male rats were fed for 7 d diets containing amounts of retinyl acetate or beta-carotene that were 1 (control), 10, 100 and 1000 times the NRC recommended requirement. No responses of the jejunal CRBP(II) level to an intake of excess vitamin 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 greater in rats fed 100 and 1000 times the vitamin A requirement than in controls. 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 greater 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 small deposition of unesterified retinol and retinyl palmitate in the jejunum. 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.(ABSTRACT TRUNCATED AT 250 WORDS)