Hepatocytes vitamin accumulation

The sinusoids transport both portal and arterial blood to the hepatocytes. The systemic blood delivered to the liver contains nutrients, drugs, and ingested toxins. The liver processes the nutrients (carbohydrates, proteins, lipids, vitamins, and minerals) for either immediate use or for storage, while the drugs and toxins are metabolized through a variety of processes known as first-pass metabolism. The liver also processes metabolic waste products for excretion. In cirrhosis, bilirubin (from the enzymatic breakdown of heme) can accumulate this causes jaundice (yellowing of the skin), scleral icterus (yellowing of the sclera), and tea-colored urine (urinary bilirubin excretion). 

Critical to vitamin D3 action is its further metabolic conversion to more active compounds (Figure 1.3). Via its transport by DBP, vitamin D3 accumulates in the liver [48]. In rats, as much as 60-80% of an injected or oral dose of vitamin D3 locates to the liver [49-51], Intestinal absorption of vitamin D3 is in association with the chylomicron fraction via the lymphatic system. Vitamin D3 is delivered to the liver in blood from the thoracic duct only a few hours post ingestion [44], A specific portion of hepatic vitamin D3 in the rat is converted to 25-OH-D3 by a 25-hydroxylase system in the endoplasmic reticulum of hepatocytes [52, 53]. This enzyme (Km 10"8 M) is regulated to an extent by 25-OH-D3 and its metabolites. Higher concentrations of vitamin D3 are handled by a second 25-hydroxylase located in liver mitochondria [54], This enzyme, also known as CYP27, 27-hydroxylates cholesterol and thus appears less discriminating than the microsomal 25-OHase which does not use cholesterol as substrate [55, 56]. In humans, however,... 

Liver function tests showed increased values after high doses of vitamin A acid (6 -). By electron microscopical investigation in 2 patients with chronic hypervita-minosis A peri-sinusoidal fibrosis and massive accumulation of lipid-storing cells were found. Impairment of blood flow by peri-sinusoidal fibrosis probably resulted in the secondary alterations in hepatocytes which included cellular atrophy and formation of cytoplasmic bullae. Histological examination of liver biopsy material revealed besides peri-sinusoidal fibrosis central vein sclerosis and focal congestion associated with peri-sinusoidal storage. The vitamin A concentration of the liver was found to be increased to 1700—2200/ig/g wet liver (11, 12 ). 

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