Stefan Wohlfeil

Comparison of the Effects of the Thrombin Inhibitor r-Hirudin in Four Animal Models of Neointima Formation After Arterial Injury

Thrombin has been implicated as a contributing factor to restenosis after vessel reopening procedures. We compared the ability of the direct thrombin inhibitor recombinant (r-) hirudin to reduce neointimal growth in different animal models of arterial injury. Carotid arteries of rats, rabbits, and hypercholesterolemic minipigs were injured by withdrawal of an inflated balloon catheter. In addition, we used a double-lesion model in rabbits, which involved balloon angioplasty of a preexisting lesion induced by carotid denudation 4 weeks earlier. r-Hirudin was given in all four animal models as a short-term application (bolus of 1 mg/kg i.v. immediately before injury, followed by infusion of 1 mg.kg-1.h-1 for 2 hours, and an injection of 6 mg/kg SC). Additionally, we investigated the effects of prolonged treatment (intravenous infusion for 3 and 14 days) in rats. Inhibition of thrombin was monitored by determination of activated partial thromboplastin time, and histomorphometric analysis of the arteries was performed after 2 (rats) or 4 (rabbits and minipigs) weeks. In rabbits, short-term r-hirudin treatment reduced neointimal area by 59% (single-injury model, P = .05) and 44% (double-injury model, P = .02). In rats and minipigs no inhibition of neointimal growth was observed after short-term r-hirudin application. A 3- or 14-day infusion of r-hirudin in rats, however, resulted in 25% (P = .007) and 27% (P = .003) reductions in neointimal area, respectively. In conclusion, there is considerable interspecies variation in the time frame of susceptibility for reduction of neointimal growth by inhibition of thrombin after arterial injury. These results demonstrate the importance of testing potential antirestenotic treatments in an array of different animal models.

The elevation of cyclic GMP as a response to acute hypervolemia is blocked by a monoclonal antibody directed against atrial natriuretic peptides.

Substantial volume expansion in conscious rats induces a strong diuresis and natriuresis that is caused by the increase in plasma levels of atrial natriuretic peptides (ANP) as measured by a radioimmunoassay. This renal response could be blocked by monoclonal antibodies directed against ANP. Parallel to the change in ANP, the cyclic GMP levels in plasma, urine and kidney tissue were increased after volume loading and reduced after additionally given antibodies. From this study it seems to be clear that the cyclic GMP rise is not a direct effect of volume expansion but is specifically mediated by the released ANP.

Effect of protein kinase inhibitors on ACTH-stimulated aldosterone production in rat zona glomerulosa cells

In order to obtain further evidence for the involvement of protein kinases in the short-term ACTH-stimulated aldosterone synthesis in rat zona glomerulosa cells, the effects of three different compounds with protein kinase inhibitory properties were investigated. Staurosporine, H-7 and trifluoperazine inhibited ACTH-stimulated aldosterone release in a dose-dependent manner. While the inhibitory effect of H-7 was reversible upon washing of the cells with inhibitor-free medium, the inhibition was maintained in cells treated with staurosporine or trifluoperazine. In contrast to the stimulated production, basal release of aldosterone even at the highest drug concentrations tested was not completely inhibited. We thus conclude that protein kinases may play a crucial role in short-term ACTH-stimulated aldosterone production in rat glomerulosa cells.