Effect of experimental renal dysfunction on bioavailability of ajmaline in rats

The effect of renal dysfunction on the bioavailability of ajmaline has been investigated in rats, where experimental renal dysfunction was induced by subcutaneous injection of uranyl nitrate (10 mg kg^-1). Renal dysfunction did not cause any change in the blood ajmaline concentration after intravenous administration (2 mg kg^-1), but it increased the blood ajmaline concentration by approximately 2.8-fold after intraduodenal administration (10 mg kg^-1). The availability of ajmaline in control rats was 16.7%, whereas the availability was increased to 41.1% in rats with renal dysfunction. The unbound fraction in the blood and the metabolic activity in the liver, was assessed with the 10 000-g supernatant fraction and with isolated hepatocytes, respectively. The values were found to be similar in both groups. The blood concentration following intraportal infusion was only slightly increased in rats with renal dysfunction, but the hepatic first-pass extraction was infusion rate-dependent and saturable. The initial absorption rate of ajmaline from the small intestine in rats with renal dysfunction was significantly greater compared with control rats. These results indicated that the increased availability of ajmaline in renal dysfunction was mainly a result of partially saturated extraction in the liver, which was caused by an increased absorption rate in the intestine and non-linear extraction in the liver.