Effects of vitamin A deficiency on plasma glucose, insulin and leptin in rats

Abstract

We have observed that vitamin A and its catalytic metabolites synergize with insulin to induce hepatic glucokinase gene expression. It has been known that retinoic acid (RA) can stimulate the expression of phosphoenolpyruvate carboxyl kinase gene. To better understand the role of vitamin A in glucose and lipid homeostasis, Zucker lean (female) rats were fed with vitamin A deficient (VAD) diet (TestDiet, #5822) and vitamin A sufficient (VAS) control diet (TestDiet, #5755) after weaning. When body weight gain stops in VAD group (a sign of vitamin A deficiency), animals were used to access the effect of vitamin A deficiency on glucose and lipid metabolism. All animals were fasted for six hours before their plasma and tissue samples were collected for analysis. To this end, levels of plasma glucose (153 ± 35.1 mg/dl), insulin (0.6 ±0.35 ng/ml), and leptin (1.3 ± 0.64 ng/ml) of VAD rats were all significantly lower than those (glucose, 176 ± 23.1 mg/dl; insulin, 1.3 ± 0.6 ng/ml; 4.0 ± 2.1 ng/ml, all P<0.04)) of VAS fed rats. When VAD rats were fed with VAS diet, the plasma glucose level (150 ± 40 mg/dl) of VAD rats was significantly increased at three days (207 ± 62 mg/dl) and seven days (221 ± 45 mg/dl) after initiation of VAS diet (all P<0.05). At the same time, plasma cholesterol level (49.6 ± 4.4 mg/dl) of VAD rats was also significantly increased at three days (74.6 ± 8.8 mg/dl) and seven days (83.9 ± 9.2 mg/dl) after resuming the VAS diet (all P<0.004). These results demonstrated that vitamin A deficiency can result in the changes of plasma glucose and lipid homeostasis. Further work is warranted to understand the underlying molecular mechanisms.