AIM: To investigate the changes of microvascular architecture, ultrastructure and permeability of rat jejunal villi at different ages. METHODS: Microvascular corrosion casting, scanning electron microscopy, transmission electron microscopy and Evans blue infiltration technique were used in this study. RESULTS: The intestinal villous plexus of adult rats consisted of arterioles, capillary network and venules. The marginal capillary extended to the base part of the villi and connected to the capillary networks of adjacent villi. In newborn rats, the villous plexus was rather simple, and capillary network was not formed. The villous plexus became cone-shaped and was closely arrayed in ablactation rats. In adult rats, the villous plexus became tongue-shaped and was enlarged both in height and width. In aged rats, the villous plexus shrank in volume and became shorter and narrower. The diametral ratio of villous arteriole to villous venule increased as animals became older. The number of endothelial holes, the thickness of basal membrane and the permeability of microvasculature were increased over the entire course of development from newborn period to aged period. CONCLUSION: The digestive and absorptive functions of the rat jejunum at different ages are highly dependent upon the state of villous microvascular architecture and permeability, and blood circulation is enhanced by collateral branches such as marginal capillary, through which blood is drained to the capillary networks of adjacent villi.

Non-transferrin-bound iron (NTBI) overtaken by heart cells might be a key cause leading to iron-mediated injury in heart disorders. NTBI uptake by heart cells might be mediated by divalent metal transporter 1 (DMT1). The understanding of the role ofDMT1in heart iron metabolism is fundamental for elucidating the cause resulting in excessive iron in the heart. The study was to evaluate effects of age and dietary iron on DMT1 mRNA expression and protein synthesis in rat heart. DMT1 mRNA expression was determined by RT-PCR and sequence analysis, and DMT1 protein by Western blot analysis. DMT1 mRNAs with or without iron-responsive element (IRE) both were found in rat heart. Expression of two forms ofDMT1mRNAs was the lowest at the age of post-natal day (PND) 7, and then increased with the age, reaching the highest at PND196 (non-IRE form) and PND63 (IRE form), respectively. During different ages, the levels ofDMT1(IRE)mRNAwere higher than those ofDMT1(non-IRE)mRNAand were significantly correlated with the non-heme iron contents in the heart. After fed a high iron for 6 weeks, the rats had a sixfold elevation in heart iron and 22% (non-IRE from) and 40% (IRE from) reduction in DMT1protein compared to the controls. Alow iron diet for 6-weeks caused cardiac hypertrophy and heart iron deficiency and also an increase in levels of two forms of DMT1 proteins. However, iron status had no significant effect on DMT1 (IRE) and DMT1 (non-IRE) mRNAs expression in the heart, although it can significantly influence heart transferrin receptor (TfR) mRNA expression. The results demonstrated that DMT1 mRNAs expression in the heart is age-dependent and that two forms of DMT1 mRNAs both are regulated by iron on the post-transcriptional level only.