Vitamin A

Vitamin A (Vitamin A1) is an endogenous metabolite. In Vitro:It is found that contribution of hepatic microsomes (RDHs) to Retinol metabolism is greater than that of cytosol (ADHs), evidenced by higher Cl_int (V_max/K_m) of Vitamin A formation in microsomes than in cytosol^[1]. In Vivo:The results show that compare with control (CON) rats, high-fat diet (HFD) significantly lowers basal level of Vitamin Al in plasma, but markedly elevates basal levels of Retinol in kidney, adipose tissue and liver. The results show that Vitamin Al absorption in HFD rats is faster than that in CON rats, evidenced by significantly shorter T_max (3.0±0.0 h for HFD rats vs 5.8±1.1 h for CON rats, p<0.05)^[1]. The plasma Vitamin A levels in methionine-choline deficient diet (MCD) rats are significantly lower than in the controls while the hepatic Vitamin A levels in MCD rats are markedly higher. The hepatic expression of Retinol-metabolizing enzymes and binding proteins (GRBP-I, ALDH1A1, and ALDH1A2) in MCD rats is significantly higher than that in control rats^[2].