Aspects récents de l'hémochromatose idiopathique

Acute infusions of bile salts increase biliary excretion of iron in iron-loaded rats

The mechanisms of biliary excretion of iron are not well known. The aim of this study was to examine the effect of choleresis induced by several agents on biliary iron excretion in iron-loaded rats. Iron overload was obtained with a diet supplemented by 3% iron carbonyl during a 6-week period. Bile was collected with an external bile fistula. Biliary iron concentration was measured by atomic absorption spectrophotometry, and hepatic iron concentration was measured by a chemical method. Compared with controls, iron overload resulted in a 14-fold increase in hepatic iron concentration but only a 3.9-fold increase in biliary iron output. In iron-loaded rats, taurocholate infusion caused a 1.8-fold significant increase in biliary iron output. Dehydrocholate, given at the same dose, induced a significant but less pronounced (1.3-fold) increase in biliary iron output in spite of a higher bile flow. Taurochenodeoxycholate, tauroursodeoxycholate, and tauro-7-ketolithocholate induced an increase in biliary iron output similar to that observed with taurocholate. The canalicular bile salt-independent choleretic dihydroxydibutyl ether caused a significant but less pronounced increase in biliary iron output (1.4-fold). These results confirm that in iron-loaded rats biliary iron excretion is increased much less than hepatic iron concentration. They show that in iron loaded rats (a) bile salts can increase biliary iron secretion, and (b) this increase is related in part to choleresis and in part to bile salts themselves. This increase may be related to an interaction of iron with bile salt monomers and/or micelles.

Evaluation of computed tomography in the assessment of liver iron overload. A study of 46 cases of idiopathic hemochromatosis

The aim of the present study was to evaluate the effectiveness of single-energy computed tomography in determining iron overload in idiopathic hemochromatosis, with special reference to slightly overloaded cases. Liver attenuation was determined in 100 patients (46 cases of idiopathic hemochromatosis, 32 cases of chronic liver disease, and 22 normal controls). The iron load was determined for the first two groups by biochemical determination of liver iron concentration (performed in all but 12 subjects in the chronic liver disease group) and hepatic histologic grading. The main results for liver attenuation (upper normal limit, 72 Hounsfield units) showed that despite a high specificity (0.96), this parameter was of low sensitivity (0.63). Although mean liver attenuation in idiopathic hemochromatosis (77 +/- 14) was significantly higher than in chronic liver diseases (53 +/- 17; p less than 10(-4) and normal controls (66 +/- 3; p less than 10(-3], and despite an overall good correlation between liver attenuation and liver iron concentration (r = 0.72; p less than 10(-3], liver attenuation was unable to detect moderate iron overload. Fourteen of 18 patients with a liver iron concentration of less than 150 mumol/g dry liver wt had liver attenuation values of less than 72. Moreover, 3 of 18 subjects with a liver iron concentration of greater than 150 had a liver attenuation of less than 72. Of these 17 false-negatives, only 7 could be attributed to associated steatosis. On the whole, single-energy computed tomography, when used on a routine basis for diagnosing iron overload, is of limited clinical value in idiopathic hemochromatosis due to its poor sensitivity. Hepatic histologic examination together with biochemical determination remains the most accurate means to assess liver iron.