Endogenous ouabain and the renin-angiotensin-aldosterone system: distinct effects on Na handling and blood pressure in human hypertension.
OBJECTIVE
To evaluate whether the renin-angiotensin-aldosterone system (RAAS) and endogenous ouabain system differently affect renal Na handling and blood pressure.


METHODS
Three hundred and one patients in whom we compared blood pressure, and renal Na tubular reabsorption in the basal condition and 2 h (T120) after saline infusion.


RESULTS
Following multivariate-adjusted linear and quartiles analysis, baseline mean blood pressure (MBP) was significantly higher (113.7 ± 1.33 mmHg) in the fourth versus the first endogenous ouabain quartile (103.8 ± 1.04 mmHg) and the trend across the quartiles was highly significant (β = 0.23, P = 3.53e-04). In contrast, an inverse relationship was present in the renin activity (PRA) quartiles with MBP highest in the first (112.5 ± 1.26) and lowest in the fourth PRA quartile (107.6 ± 1.48, P = 0.039). Following an acute saline load, changes in MBP and the slope of the pressure-natriuresis relationship were inversely related across the PRA quartiles. The fractional excretion of sodium (FENa) showed a negative linear trend going from the first to the third endogenous ouabain quartiles (2.35 ± 0.17 and 1.90 ± 0.14%, P = 0.05). Patients in the fourth endogenous ouabain quartile (>323 pmol/l) showed increased FENa T120 (2.78 ± 0.18%, P < 0.01) and increased Na tubular rejection fraction (P = 0.007) after Na load. After the saline load, there was a biphasic relationship between plasma endogenous ouabain and FENa favoring Na retention at low endogenous ouabain and Na excretion at high endogenous ouabain levels.


CONCLUSIONS
The RAAS and endogenous ouabain system are two independent and complementary systems having an inverse (RAAS) or a direct (endogenous ouabain system) relationship with hemodynamic parameters.
Manunta
Paolo
P
Nephrology, and Dialysis San Raffaele Scientific Institute, Università Vita-Salute San Raffaele, Milan, Italy. manunta.paolo@hsr.it
Hamlyn
John M
JM
Simonini
Marco
M
Messaggio
Elisabetta
E
Lanzani
Chiara
C
Bracale
Maria
M
Argiolas
Giuseppe
G
Casamassima
Nunzia
N
Brioni
Elena
E
Glorioso
Nicola
N
Bianchi
Giuseppe
G
D000328:Adult; D000450:Aldosterone / Q000097:blood; D001794:Blood Pressure / Q000502:physiology; D005260:Female; D006801:Humans; D006973:Hypertension / Q000097:blood / Q000503:physiopathology*; D007684:Kidney Tubules / Q000503:physiopathology; D016014:Linear Models; D008297:Male; D008875:Middle Aged; D009318:Natriuresis / Q000502:physiology; D010042:Ouabain / Q000097:blood*; D012083:Renin / Q000097:blood; D012084:Renin-Angiotensin System / Q000502:physiology*; D012964:Sodium / Q000097:blood / Q000378:metabolism
D000450:Aldosterone; D010042:Ouabain; D012964:Sodium; D012083:Renin