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

Abstract

Background

In a previous study, we showed that a saponin mixture isolated from the roots of Ampelozizyphus amazonicus Ducke (SAP AaD) 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 AaD- induced antidiuresis in rats.

Methods

To evaluate the effect of SAP AaD 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 AaD ( SAPAaD + Furo) or 0.5 ml of 0.9 % NaCl ( NaCl + Furo). In the SAPAaD + NaCl group, rats were pretreated with SAP AaD 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 AaD, rats were given the physiological solution (as above) containing SAP AaD (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.

Results

It was observed that SAP AaD inhibited furosemide-induced diuresis (at 90 min: from 10.0 ± 1.0 mL, NaCl + Furo group, n = 5, to 5.9 ± 1.0 mL, SAPAaD + Furo 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 AaD 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.

Conclusion

We concluded that the SAP AaD 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.