Marinobufagenin is related to elevated central and 24-h systolic blood pressures in young black women: the African-PREDICT Study

Marinobufagenin (MBG) is an endogenous steroidal α1-Na⁺K⁺-ATPase inhibitor. Because of its role in sodium handling, MBG has been associated with both antihypertensive and prohypertensive effects in normal physiology and pathology. MBG is positively associated with blood pressure in Dahl salt-sensitive rats exhibiting a similar hypertensive phenotype to black populations, characterized by impaired urinary Na⁺ excretion. However, clinical studies exploring blood pressure (BP)-related effects of MBG in black populations are scant. We determined whether the MBG/Na⁺ ratio (assessing the effectiveness of Na⁺ excretion resistance to MBG) is related to systolic BP (SBP) in young black men and women, compared to whites. We included 331 apparently healthy participants (20-30 years) (42.9% black, 43.8% men) on a habitual diet. We obtained 24-h and central SBP, and 24-h urinary Na⁺ and MBG levels. We found no ethnic differences in MBG, Na⁺ or MBG/Na⁺. MBG excretion correlated positively with Na⁺ excretion in all groups and to SBP in white men and black women (p ≤ 0.011). In black women only SBP related positively to MBG/Na⁺ in single and multi-variable adjusted regression models: central SBP (R² = 0.26; ß = 0.28; p = 0.039), 24-h SBP (R² = 0.46; ß = 0.30; p = 0.011), daytime (R² = 0.38; ß = 0.28; p = 0.023) and nighttime SBP (R² = 0.38; ß = 0.33; p = 0.009). In contrast, inverse associations of MBG/Na⁺ with nighttime SBP were evident in white women (r = -0.20; p = 0.038) but lost significance after multiple adjustments (R² = 0.36; ß = -0.13; p = 0.12). We found independent positive associations of SBP with MBG/Na⁺ in black women. This data supports the concept that reduced MBG-mediated Na⁺ excretion can contribute to adverse hemodynamics.