Retinol is sequestered in the bone marrow of vitamin A-deficient rats

Abstract

Retinoic acid bound to the nuclear retinoic acid receptor-α is required for the differentiation of promyelocytes to mature neutrophils. However, severely vitamin A-deficient rats have normal numbers of neutrophils in the blood and inflamed tissues. This paradox was explored using four dietary groups of rats: 1) vitamin A-deficient rats; 2) vitamin A-deficient rats subsequently receiving vitamin A; 3) weight-matched pair-fed rats; and 4) nonrestricted, vitamin A-complete diet-fed rats. Plasma and liver retinol concentrations of the vitamin A-deficient rats were <1% of those of the other three groups. In contrast, the bone marrow retinol concentrations of the vitamin A-deficient rats were fourfold higher than those in the other three groups. The distribution of myeloid-derived cells in the bone marrow was similar in all four groups of rats with the exception of a significantly greater (P < 0.05) occurrence of hypersegmented neutrophils (six or more lobes) in the vitamin A-deficient rats (2.1%) relative to the control groups (0-0.1%). The blood of the vitamin A-deficient rats also contained significantly higher numbers (P < 0.01) of hypersegmented neutrophils (67%) relative to those in the control groups (2-7%). The hypersegmentation of the neutrophils in this group of rats was not due to a concurrent deficiency of vitamin B-12 or folate. The importance of bone marrow-derived cells to the survival of the animal is suggested by retinol sequestration in the bone marrow of vitamin A-deficient rats, allowing the differentiation of myeloid cells to neutrophils.