Renal haemodynamics and natriuretic responses to intravenous administration of diadenosine tetraphosphate (Ap4A) and nicotinamide adenine dinucleotide (NAD) in rat.

Effects of Ap4A and NAD--precursor of adenosine, on renal plasma flow (RPF), glomerular filtration rate (GFR) and urine excretion were determined in the anaesthetised rats. Infusion of Ap4A or NAD (i.v., bolus--1 micromol/kg followed by 10 nmol/min/kg) decreased RPF and GFR (by 30 and 40%, respectively). In spite of GFR reduction during Ap4A infusion, the significant increase in sodium excretion and urine flow was noticed: fractional sodium (FENa) and urine excretion (FEurine) rose 15-fold and 2.5-fold in comparison with the control value, respectively. In contrast to Ap4A, NAD-induced decrease in GFR was associated with parallel decrease in sodium and urine excretion, thus the FENa and FEurine did not significantly change. Pretreatment with adenosine deaminase (adenosine degrading enzyme, 2 U/min/kg) or theophylline (P1-receptors antagonist, 0.2 mmol/min/kg) ceased responses to NAD, whereas Ap4A-induced changes were not affected. Pre-treatment with suramin (P2-receptors antagonist, (i.v., bolus--12 mg/kg followed by 1.2 mg/min/kg) completely abolished the renal effects of Ap4A. We conclude that Ap4A may exert specific action on renal function. It acts different from NAD that modified renal function through its hydrolysis product--adenosine. Ap4A might reduce glomerular filtration rate and evoke natriuresis and diuresis, and its effects are probably mediated through stimulation of P2-receptors.

Experimental model of hepatic venoocclusive disease (VOD) caused by dactinomycin--preliminary report about hepatoprotective effect of amifostine.

UNLABELLED: The purpose of the study was elaboration of the experimental model of hepatic venoocclusive disease (VOD) induced by dactinomycin and investigation of possible hepatoprotective effects of amifostine and heparin individually or in combination with dexamethasone. 198 Wistar strain male rats were used in the trial in two series of experiments. In the first series the experimental model of VOD induced by dactinomycin was elaborated on the group of 18 animals (divided into 3 groups receiving intraperitoneally isotonic salt solution, dactinomycin or nitrosamine). Nitrosamine--a well-known agent causing VOD--was used as positive control. Open biopsies of the liver and blood collections were repeated in order to determine liver enzymes' concentrations. Histopathological examinations demonstrated that dactinomycin caused liver lesion corresponding with VOD picture. Second series of animals was divided into 6 groups receiving the following drugs: I--0.9% NaCl solution, II--dactinomycin (ACT), III--ACT + fraxiparine s.c., IV--ACT + fraxiparine + dexamethasone, V--ACT + amifostine. Five animals from each group were sacrificed on the 3rd and 7th day after each cycle of drug administration. Blood was drawn in order to determine the following: AspAT, AlAT, Falk, GGTP and LDH. Intravital wedge biopsies under anesthesia with the use of inactin were also performed. Liver samples were stained with the use of H&E, p. a. S and Gomory's techniques. We did not find significant differences in liver enzymes' levels between the groups. Pathological changes corresponding with VOD picture of different intensification were found in liver samples from all the rats receiving ACT. Changes became more and more intensive after consecutive cycles. Lesion of central veins' and liver sinusoids' endothelium dominated. Fraxiparine administered individually or in combination with dexamethasone did not prevent the lesion. Administration of amifostine before ACT decreased pathomorphological changes in liver. Dactinomycin caused homogenous subclinical liver lesion corresponding with VOD. It may also occur in children receiving ACT in the course of nephroblastoma's treatment. But probably the changes are too subtle to manifest themselves clinically with exception of patients particularly sensitive (for example after previous radiotherapy). Lack of differences observed in liver enzymes' levels between the groups supports the explanation. Markers of lesion of liver vessels' endothelium should be looked for to make more specific diagnostics of VOD possible. Hepatoprotective properties of amifostine need further studies. CONCLUSIONS: 1. It is possible to create the experimental model of VOD induced by dactinomycin administration. 2. Amifostine seems to act hepatoprotectively to liver lesions caused by dactinomycin.