The effect of saponins from <it>Ampelozizyphus amazonicus</it> Ducke on the renal Na⁺ pumps’ activities and urinary excretion of natriuretic peptides

<p>Abstract</p> <p>Background</p> <p>In a previous study, we showed that a saponin mixture isolated from the roots of <it>Ampelozizyphus amazonicus</it> Ducke (SAP<it>Aa</it>D) reduces urine excretion in rats that were given an oral loading of 0.9 % NaCl (4 ml/100 g body weight). In the present study, we investigated whether atrial natriuretic peptides (ANP) and renal ATPases play a role in the SAP<it>Aa</it>D- induced antidiuresis in rats.</p> <p>Methods</p> <p>To evaluate the effect of SAP<it>Aa</it>D on furosemide-induced diuresis, Wistar rats (250-300 g) were given an oral loading of physiological solution (0.9 % NaCl, 4 ml/100 g body weight) to impose a uniform water and salt state. The solution containing furosemide (Furo, 13 mg/kg) was given 30 min after rats were orally treated with 50 mg/kg SAP<it>Aa</it>D (<it>SAPAaD + Furo</it>) or 0.5 ml of 0.9 % NaCl (<it>NaCl + Furo</it>). In the <it>SAPAaD + NaCl</it> group, rats were pretreated with SAP<it>Aa</it>D and 30 min later they received the oral loading of physiological solution. Animals were individually housed in metabolic cages, and urine volume was measured every 30 min throughout the experiment (3 h). To investigate the role of ANP and renal Na⁺ pumps on antidiuretic effects promoted by SAP<it>Aa</it>D, rats were given the physiological solution (as above) containing SAP<it>Aa</it>D (50 mg/kg). After 90 min, samples of urine and blood from the last 30 min were collected. Kidneys and atria were also removed after previous anesthesia. ANP was measured by radioimmunoassay (RIA) and renal cortical activities of Na⁺- and (Na⁺,K⁺)-ATPases were calculated from the difference between the [³²P] Pi released in the absence and presence of 1 mM furosemide/2 mM ouabain and in the absence and presence of 1 mM ouabain, respectively.</p> <p>Results</p> <p>It was observed that SAP<it>Aa</it>D inhibited furosemide-induced diuresis (at 90 min: from 10.0 ± 1.0 mL, <it>NaCl + Furo</it> group, n = 5, to 5.9 ± 1.0 mL, <it>SAPAaD + Furo</it> group n = 5, p < 0.05), increased both Na⁺-ATPase (from 25.0 ± 5.9 nmol Pi.mg^-1.min^-1, control, to 52.7 ± 8.9 nmol Pi.mg^-1.min^-1, p < 0.05) and (Na⁺,K⁺)-ATPase (from 47.8 ± 13.3 nmol Pi.mg^-1.min^-1, control, to 79.8 ± 6.9 nmol Pi .mg^-1.min^-1, p < 0.05) activities in the renal cortex. SAP<it>Aa</it>D also lowered urine ANP (from 792 ± 132 pg/mL, control, to 299 ± 88 pg/mL, p < 0.01) and had no effect on plasma or atrial ANP.</p> <p>Conclusion</p> <p>We concluded that the SAP<it>Aa</it>D antidiuretic effect may be due to an increase in the renal activities of Na⁺- and (Na⁺,K⁺)-ATPases and/or a decrease in the renal ANP.</p