Sodium homeostasis in dogs with chronic renal insufficiency

Changes in Total Sodium Intake Do Not Lead to Proportionate Changes in Total Sodium Removal in CAPD Patients

Background

Dietary salt and fluid restriction is important in controlling fluid balance in patients on continuous ambulatory peritoneal dialysis (CAPD). However, it is often difficult to monitor patients’ dietary total sodium intake (TSI). Usually, total sodium removal (TSR), the sum of urinary sodium removal (USR) and dialysate sodium removal (DSR), is suggested to represent TSI. In the present study, we investigated the reliability of using TSR as a surrogate to TSI in CAPD patients.

Methods

40 clinically stable CAPD patients were closely followed for 3 months. Their TSI, USR, DSR, and fluid status were measured twice: at baseline and at the end of this study respectively. Fluid status was evaluated by bioimpedance analysis. Patients with increased sodium intake (group ISI) or decreased sodium intake (group DSI) (both >0.5 g/day or >21.74 mmol/day elemental sodium) were included in this study.

Results

There were 15 patients in group ISI and 9 patients in group DSI. During the follow-up, although TSI increased in group ISI and decreased in group DSI ( p < 0.05), there were no significant changes in USR, DSR, or TSR in either group. No relationship was found between TSI and TSR. Changes in weight, blood pressure, urine volume, ultra-filtration, and small solute removal (Kt/V and creatinine clearance) were not statistically significant between the two groups. Fluid status deteriorated in group ISI and improved in group DSI ( p < 0.05).

Conclusions

Our study suggests that changes in total sodium intake do not lead to proportionate changes in total sodium removal in CAPD patients. Therefore, TSR (the sum of USR and DSR) should be used cautiously to monitor TSI in this patient population.

[Effect of dietary sodium intake on residual renal function in patients undergoing peritoneal dialysis: a prospective study of 33 cases]

OBJECTIVE

To explore the impact of dietary sodium-intake on residual renal function in patients undergoing peritoneal dialysis (PD).

METHODS

Thirty-three patients on PD with stable dialysis were regularly followed up for 12 months. The daily sodium intake of the patients was calculated based on the 3-day dietary record. Based on the mean daily sodium intake, the patients enrolled were divided into low-salt group (sodium intake≤3.0 g/day, 19 patients) and high-salt group (sodium intake&gt;3.0 g/day, 14 patients). The baseline data of the patients were recorded, and the indicators of residual renal function and peritoneal function were regularly tested. The patients were followed-up at 3-month intervals, and their urine volume, peritoneal ultrafiltration volume and other clinical indicators were recorded and the biochemical indexes were detected to evaluate the changes in the residual renal function and peritoneal function.

RESULTS

There was a positive correlation between the total sodium excretion and dietary sodium intake in these patients (r=0.536, P=0.0013), and sodium excretion by dialysis was positively correlated with their sodium intake (r=0.901, P=0.000). Regression analysis suggested that the total sodium excretion was correlated with dietary sodium intake (β=0.416, 95% CI: 0.170-0.666; P &lt; 0.0018); sodium excretion by dialysis was associated with dietary sodium intake (β=0.489, 95% CI: 0.395-0.582; P &lt; 0.001). The residual renal function was reduced by 17.48±11.22 L /(w·1.73 m²) in the low-salt group, as compared to 30.20±18.30 L /(w·1.73 m²) in the high-salt group (P=0.032). The reduction in the residual renal function was correlated with sodium intake in the PD patients (r=0.409, P=0.018). Multivariate regression analysis showed that sodium intake was an independent factor contributing to the reduction of residual renal function (β=14.646, 95% CI 7.426-21.866, P &lt; 0.001).

CONCLUSIONS

Sodium excretion by PD in patients with continuous ambulatory PD is positively correlated with their dietary sodium intake, which contribute to the decrease of residual renal function. A high dietary sodium intake may accelerate the reduction of residual renal function in these patients.

Effect of uremia on aldosterone metabolism in the isolated perfused rat liver

The effect of uremia on hepatic metabolism of aldosterone was studied in the isolated perfused liver of female Wistar rats. Uremia was induced by five-sixths partial nephrectomy 4 weeks before experiments. Isolated livers of normal and uremic rats were perfused at a constant flow rate with a hemoglobin-free medium, to which 4-14C-D-aldosterone was added at 3 nmol/L. Aldosterone was analyzed by radioimmunoassay (RIA) and 4-14C-D-aldosterone radiometabolites in perfusate and bile were assayed by high-performance liquid chromatography (HPLC). Uremic rats had a 10% lower body weight (P < .01) and increased plasma urea, creatinine, and parathyroid hormone (PTH) levels (258%, 200%, and 208%, respectively; P < .01-.001). Blood pressure and plasma K+, Na+, and aldosterone levels were similar. Plasma renin activity was suppressed by 68% in uremic rats (P < .001). Liver wet weight and hepatic function were similar in livers of both groups of rats. Hepatic elimination of aldosterone was compatible with a first-order kinetics. Hepatic clearance of aldosterone per liver and per gram liver was similar; however, when expressed per 100 g rat body weight, a 21% higher value was observed in uremic rats (11.6 +/- 1.8 mL/min) compared with normal rats (9.6 +/- 1.5 mL/min, P < .01). Polar aldosterone radiometabolites accumulated in the perfusate to approximately 40% of the initial 14C added at 15 minutes, and were eliminated in bile at a similar rate in both groups. No qualitative difference was found in the pattern of radiometabolites of aldosterone in perfusate and bile.(ABSTRACT TRUNCATED AT 250 WORDS)