Plasma Renin, Angiotensin II, Aldosterone and Atrial Natriuretic Peptide Concentrations on Acute Salt-Loading in Normotensive and Hypertensive Nigerians

Blacks have a delayed ability to excrete salt when compared with whites despite comparable levels of renal function. The basis is not fully understood. Salt retention is a major cause of hypertension. This study aimed to assess and compare renin, angiotensin II, aldosterone and atrial natriuretic peptide concentrations on acute saltloading in normotensive and hypertensive Nigerians. Forty-three (43) apparently healthy normotensive and thirtyseven (37) newly diagnosed age-matched hypertensive Nigerian volunteers ingested 11.6g of salt each per day for 5 days. Plasma concentrations of renin, angiotensin II, aldosterone and atria natriuretic peptide were determined before and after salt salting in the participants. The results showed basal plasma renin concentrations to be similar and salt loading did not raise its levels in the study population. Besides, basal angiotensin II hormone concentrations were not different but salt loading increased its levels significantly (p < 0.001) in normotensive and hypertensive participants. However, the mean change in the angiotensin levels after salt loading was significantly higher (p < 0.05) in hypertensive than normotensive volunteers. Basal aldosterone concentrations were higher (p < 0.05) in normotensive participants but its levels were more suppressed in the normotensive (p < 0.001) than hypertensive (p < 0.01) participants. Basal atria natriuretic peptide concentrations were also similar but salt loading significantly elevated the hormone levels (p < 0.001) in normotensive participants only and its mean change after salt loading, was also significantly higher (p < 0.05) in the normotensive participants. In conclusion, acute salt loading did not suppress plasma renin, angiotensin II; and ANP levels were not significantly raised in the hypertensive Nigerians. These findings suggest the basis for the racial difference in renal salt handling.

Key Words: Renin-angiotensin-aldosterone system, salt loading, hypertension, atrial natriuretic peptide.