Influence of radiographic contrast agents on absorption of bromosulfophthalein by slices of rat liver

The enzymic 5′-deiodination of 3′,5′-di-iodothyronine and 5-deiodination of 3,3′,5-tri-iodothyronine by rat liver microsomal fractions were found to be characterized by apparent Km values of 0.77 and 17.4 microM respectively, 3′,5′-Di-iodothyronine was a competitive inhibitor of 3,3′,5-tri-iodothyronine 5-deiodination (Ki 0.65 microM) and 3,3′,5-tri-iodothyronine was a competitive inhibitor of 3′,5′-di-iodothyronine 5′-deiodination (Ki 19.6 microM). In addition, several radiographic contrast agents and iodothyronine analogues inhibited both reactions competitively and with equal potencies (r = 0.999). These results strongly suggest the existence of a single hepatic deiodinase acting on both the tyrosyl and phenolic ring of iodothyronines.

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Effects of Radiographic Contrast Agents on Thrombin Formation and Activity

Thrombosis and Haemostasis ◽

10.1055/s-0037-1615186 ◽

1998 ◽

Vol 80 (08) ◽

pp. 266-272 ◽

Cited By ~ 15

Author(s):

Andrew Parker ◽

William Fay

Keyword(s):

Contrast Agents ◽

Tissue Factor ◽

Coronary Angioplasty ◽

Molecular Mechanisms ◽

Factor Viia ◽

Minor Effect ◽

Ionic Contrast ◽

Radiographic Contrast ◽

Inhibition Of Thrombin ◽

Thrombin Formation

SummaryClinical trials suggest that the risk of thrombosis during coronary angioplasty is lower with ionic contrast agents than with nonionic contrast agents. However, the molecular mechanisms underlying this effect are unknown. This study examined the effects of contrast agents on thrombin formation and its interaction with substrates, inhibitors, and ligands to define potential mechanisms by which contrast agents affect thrombus formation. Two ionic agents, diatrizoate and ioxaglate, and one nonionic agent, ioversol, were studied. Ionic agents inhibited factor X activation by the tissue factor-factor VIIa complex more potently than ioversol (53 ± 3.7, 43.0 ± 1.9, and 26.5 ± 2.4% inhibition by diatrizoate, ioxaglate, and ioversol, respectively, at concentrations of 5%). Ionic contrast agents were potent inhibitors of prothrombinase function, inhibiting thrombin formation by >75% at contrast concentrations of 0.6% (p <0.005). Ioversol inhibited prothrombinase to a significantly lesser extent than ionic agents. Clotting assays suggested that ioxaglate was the most potent inhibitor of thrombin generation in plasma despite having the least effect on fibrin polymerization. Contrast agents inhibited binding of thrombin to fibrin, with ionic agents producing a more potent effect than ioversol (p <0.02). However, contrast agents did not inhibit thrombin-mediated platelet activation, had only a minor effect on inhibition of thrombin by antithrombin III, and did not affect thrombin-hirudin interactions. In summary, these studies identify specific mechanisms by which radiographic contrast agents inhibit thrombin formation and function – i.e. inhibition of tissue factor-dependent factor Xa generation, inhibition of the prothrombinase complex, and inhibition of thrombin binding to fibrin. These findings may help to explain the reduced risk of thrombosis during coronary angioplasty associated with ionic contrast agents.

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