Endogenous Marinobufagenin-like Immunoreactive Factor and Na + ,K + ATPase Inhibition During Voluntary Hypoventilation

Abstract

In previous studies investigators found that conditioned hypoventilatory breathing potentiated a sodium-sensitive form of hypertension in dogs that was not mediated by sympathetic nervous system arousal. Our study investigated effects of 30 minutes of voluntary hypoventilation, maintained by a respiratory gas monitor and feedback procedure, in 16 normotensive humans of both sexes on (1) plasma concentrations of endogenous digitalis-like factors (ouabain-like and marinobufagenin-like immunoreactivity), (2) activity of erythrocyte Na ⁺ ,K ⁺ -ATPase, (3) inhibitory activity of plasma Na ⁺ ,K ⁺ -ATPase, and (4) blood pressure. Increased end tidal P co ₂ (41±0.78 mm Hg versus 37.6±1.03 mm Hg) was associated with (1) an increase in plasma marinobufagenin-like immunoreactivity (1.23±0.47 versus 4.96±1.19 nmol/L), (2) an inhibition of Na ⁺ ,K ⁺ -ATPase in red blood cells (3.68±0.22 versus 2.15±0.25 mmol P _i · mL ⁻¹ · h ⁻¹ ; P <.01), (3) increase in plasma Na ⁺ ,K ⁺ -ATPase inhibitory activity (34.9±4.0% versus 48.8±2.1%, P <.02), and (4) increases in systolic (112.4±2.6 versus 107.6±1.8 mm Hg) and diastolic (73.5±2.1 versus 68.8±2.1 mm Hg) blood pressures. Plasma levels of ouabain-like immunoreactivity did not increase significantly. Incubation of erythrocytes obtained during hypoventilation with antidigoxin antibody restored the Na ⁺ ,K ⁺ -ATPase activity (3.99±0.34 mmol P _i · mL ⁻¹ · h ⁻¹ ). Cessation of hypoventilation was associated with decreases in diastolic blood pressure (70.5±2.2 mm Hg) and restoration of Na ⁺ ,K ⁺ -ATPase activity in erythrocytes (2.99±0.43 mmol P _i · mL ⁻¹ · h ⁻¹ ). On the basis of organic extraction and thin-layer chromatography followed by separation with the use of reverse-phase high-performance liquid chromatography, the material coeluting with marinobufagenin was separated from human urine. This material cross-reacted with anti-marinobufagenin antibody. These results demonstrate the presence of a bufadienolide-like Na ⁺ ,K ⁺ -ATPase inhibitor in human plasma and support the view that breathing pattern may participate in blood pressure control via release of a rapidly acting circulating Na ⁺ ,K ⁺ -ATPase inhibitor.