The effect of glycerol-induced acute renal failure upon cardiac reactivity in the rat: influence of indomethacin treatment and renal pedicle ligation

Pharmacokinetics and Hepatic Extraction of Metoprolol in Rats with Glycerol-Induced Acute Renal Failure

The aim of the present study was to evaluate the effect of glycerol-induced acute renal failure (ARF) on the pharmacokinetics and hepatic extraction of metoprolol in rats. Experimental ARF in rats was induced by injections of 50% glycerol into the leg muscle (10 ml/kg). Pharmacokinetics and hepatic extraction of metoprolol was evaluated by means of intravenous, intra-intestinal, and intra-portal administration of the drug. The blood metoprolol concentration following intravenous infusion in ARF rats was similar to that in control rats. On the other hand, the blood metoprolol concentration at 5--10 min after intra-intestinal administration in ARF rats was significantly higher than that in control rats, and the oral clearance (CL/F) of the drug was significantly decreased in ARF rats. Hepatic extraction following intra-portal infusion was not altered by glycerol-induced ARF; however, hepatic first-pass extraction of metoprolol was dose-dependent and saturable in both ARF and control rats. These results suggested that the decreased CL/F of metoprolol in rats with glycerol-induced ARF is mainly a result of the increased initial absorption rate in the intestine followed by partial saturation of hepatic first-pass metabolism.

Cardiac function in rats with acute renal failure

Inotropic responses of isolated cardiac preparations from rats with glycerol-induced acute renal failure (ARF) were recorded, following a range of cardiac stimulants. Left atria of rats with ARF showed diminished inotropic responses only to the calcium agonist Bay K 8644 (methyl 1,4-dihydro-2,6-dimethyl-3-nitro-4-(2-trifluoromethyl-phenyl)-pyridine-5 -carboxylate) whilst right ventricular strips exhibited reduced responses to isoprenaline, 3-isobutyl-1-methylxanthine, Ca2+ and Bay K 8644. Investigations of cardiac mitochondrial respiration indicated that there is a site-unspecific 'pseudo' uncoupling of oxidative phosphorylation in ARF but that electron transport is unaffected. This uncoupling of oxidative phosphorylation did not have any detectable effect on either levels of total adenine nucleotides and creatine phosphate or cellular energy charge. Measurements were also made of the activity of pyruvate dehydrogenase which provides an index of mitochondrial Ca2+ levels. The proportion of pyruvate dehydrogenase in its active form was threefold higher following isoprenaline injection in hearts of rats with ARF compared with controls. The results suggest that in hearts of rats with ARF there is a change in the number, affinity, efficacy or coupling of the dihydropyridine receptor on the L-type calcium channel. Moreover, in the ventricle, a defect in cellular Ca2+ control, resulting in an increase in mitochondrial Ca2+ uptake, may contribute to the depression of inotropic response to the range of cardiac stimulants tested.

Cardiovascular responses in rats with chronic renal failure

Cardiovascular responses were determined in rats with chronic renal failure (CRF) produced by five sixths nephrectomy and in sham-operated rats. The conscious systolic blood pressure of rats with CRF was significantly higher than the pressure in controls although, after anaesthesia, there were no significant differences in the mean arterial pressure between the two groups of rats. The pressor responses to noradrenaline in rats with CRF were not significantly different from those recorded in sham-operated controls. The bradycardia elicited by electrical stimulation of the vagus nerve was significantly diminished in rats with CRF. However, indomethacin treatment (1 mg kg-1 s.c. twice daily for 2 days) abolished the differences in response to vagal stimulation. Changes in heart rate in response to electrical stimulation of the cervical sympathetic nerve and to bolus i.v. injections of isoprenaline and carbachol were similar in rats with CRF and controls. The most notable disturbance of cardiovascular function in rats with CRF is the diminished cardiac chronotropic response to vagal stimulation which appears to be mediated by a presynaptic action of prostaglandins.