Non-uniform relationship between salt status and aldosterone activity in patients with chronic kidney disease

Background: Hypertension is prevalent in chronic kidney disease (CKD). Studies suggest that reduction in dietary salt intake reduces blood pressure (BP). We studied relationships between salt intake, BP and renin angiotensin system regulation in order to establish if it is disordered in CKD. Methods: Mechanistic crossover study of CKD patients versus non-CKD controls. Participants underwent modified saline suppression test prior to randomisation to either low or high salt diet for 5 days and then crossed over to the alternate diet. Angiotensin-II stimulation testing was performed in both salt states. BP, urea and electrolytes, and plasma aldosterone concentration (PAC) were measured. Results: Twenty-seven subjects were recruited (12 CKD, 15 control). There was no difference in age and baseline BP between the groups. Following administration of intravenous saline, systolic BP increased in CKD but not controls (131 ± 16 mmHg to 139 ± 14 mmHg, p=0.016, vs. 125 ± 20 mmHg to 128 ± 22 mmHg, p=0.38). Median PAC reduced from 184 (124,340) pmol/L to 95 (80,167) pmol in controls (p=0.003), but failed to suppress in CKD (230 (137,334) pmol to 222 (147,326) pmol (p=0.17)). Following dietary salt modification there was no change in BP in either group. Median PAC was lower following high salt compared to low salt diet in CKD and controls. There was a comparable increase in systolic BP in response to angiotensin-II in both groups. Discussion: We demonstrate dysregulation of aldosterone in CKD in response to salt loading with intravenous saline, but not to dietary salt modification