The concept of the natriuretic hormone and its relation to hypertension

Pre-eclampsia has an adverse impact on maternal and fetal health

Pre-eclampsia (preE) is a multifaceted complication found uniquely in the pregnant patient and one that has puzzled scientists for years. PreE is not a single disorder, but a complex syndrome that is produced by various pathophysiological triggers and mechanisms affecting about 5% of obstetrical patients. PreE is a major cause of premature delivery and maternal and fetal morbidity and mortality. PreE is characterized by de novo development of hypertension and proteinuria after 20 weeks of gestation and affects nearly every organ system, with the most severe consequences being eclampsia, pulmonary edema, intrauterine growth restriction, and thrombocytopenia. PreE alters the intrauterine environment by modulating the pattern of hormonal signals and activating the detrimental cellular signaling that has been transported to the fetus. The fetus has to adapt to this intrauterine environment with detrimental signals. The adaptive changes increase the risk of disease later in life. This review defines the predisposition and causes of preE and the cellular signaling detrimental to maternal health during preE. Moreover, the risk factors for diseases that are transmitted to the offspring have been addressed in this review. The detrimental signaling molecules that have been overexpressed in preE patients raises the possibility that those signals could be therapeutically blocked one day.

Pathogenesis of pre-eclampsia: marinobufagenin and angiogenic imbalance as biomarkers of the syndrome

Pre-eclampsia (preE), a pregnancy disorder with the de novo onset of hypertension and proteinuria after 20 weeks of gestation, has multiple triggers that initiate pathophysiologic mechanisms. This review addresses translational aspects of preE by synthesizing information on preE pathogenesis, describing diagnostic biomarkers that predict disease, and suggesting strategies to lessen adverse outcomes. Key to this understanding is the role of cardiotonic bufodienolides, with marinobufagenin (MBG) as the prototype, and angiogenic factors in preE pathogenesis. Data from a rat model believed to mimic human preE show that urinary excretion of MBG increases before the onset of hypertension and proteinuria and that affected animals have an increased vascular leakage and blood brain barrier permeability. Angiogenic imbalance occurs with the onset of the syndrome in this model. Also, we report that MBG levels in preE patients exceed those in normal pregnancy and that angiogenic factors are altered in patients showing signs and symptoms of overt disease. In vitro administration of MBG inhibits cytotrophoblast function and triggers hyperpermeability in endothelial cell monolayers. We advance the hypotheses that MBG precedes preE; MBG causes disruption of tight junction proteins leading to vascular leak via activation of MAPK which triggers apoptotic mechanisms resulting in further endothelial dysfunction leading to edema with the release of angiogenic factors. This review provides new evidence about the role of MBG and vasoactive intermediates in preE pathogenesis including the neurologic sequela and may reveal new therapeutic targets for the prevention of preE complications.

Ouabain-Sensitive alpha1 Na,K-ATPase enhances natriuretic response to saline load

Na,K-ATPase is ubiquitously expressed and is essential for maintaining electrochemical and osmotic gradients. The alpha subunit of Na,K-ATPase is the receptor for cardiotonic steroids, which act through the ouabain-binding site and are important in cardiovascular regulation. Interestingly, the presence of endogenous Na,K-ATPase ligands has been implicated in the natriuretic response to perturbations such as hypertension and salt loading; therefore, it is important to characterize the role of the ouabain-binding sites in this context. Because the alpha1 isoform of mice and rats is relatively ouabain resistant, gene-targeting strategies were used to produce mice with reversed responses of the alpha1 and/or alpha2 isoforms to ouabain to assess for altered natriuretic responses to acute salt loading. Regardless of the sensitivity of the alpha2 isoform to ouabain, conferring ouabain sensitivity to alpha1 augmented the natriuretic response to an acute salt load. In addition, when endogenous Na,K-ATPase inhibitors were sequestered with an anti-digoxin antibody fragment, the sodium excretion rates in the ouabain-sensitive alpha1 isoform mice were equivalent to the ouabain-resistant alpha1 isoform mice. These data suggest that the ouabain-binding site of the alpha1 Na,K-ATPase can participate in the natriuretic response to a salt load by responding to endogenous Na,K-ATPase ligands.

Marinobufagenin impairs first trimester cytotrophoblast differentiation

Preeclampsia is a pregnancy-specific syndrome that is the leading cause of maternal death during pregnancy in the developed world. In preeclampsia, a combination of immunological, genetic and environmental factors can lead to altered cytotrophoblast (CTB) invasion of the uterine wall, a process that is critical for normal placental development and pregnancy maintenance. Marinobufagenin (MBG) is an endogenous inhibitor of the sodium pump Na(+)/K(+) ATPase, and increased plasma MBG is associated with hypertension, chronic renal failure and preeclampsia. In the present study, the effects of MBG on CTB differentiation and invasion were investigated utilizing the first trimester extravillous CTB cell line SGHPL-4. MBG significantly inhibited SGHPL-4 proliferation in a dose-dependent manner. In addition, growth factor-induced migration and invasion were significantly inhibited by MBG treatment. These findings demonstrate that MBG impairs CTB differentiation along the invasive pathway. Elucidating the mechanisms by which MBG impairs placental development may increase our understanding of fetal and maternal pathologies associated with preeclampsia.

Increased activity of digoxin-like substance in low-renin hypertension in acromegaly

Arterial hypertension is common in acromegaly, but the pathogenesis of this complication remains unknown. To determine the role of an endogenous Na,K pump inhibitor/digoxin-like substance (DLS) in the pathogenesis of hypertension in acromegaly 76 subjects: 28 with acromegaly, 20 with essential hypertension and 28 healthy controls were studied. Serum DLS was measured with the use of radioimmunoassay and bioassay by the inhibition of digoxin-sensitive erythrocyte 86-Rb uptake. In acromegaly, the activity of DLS was significantly increased and plasma renin activity decreased in the hypertensive group, as compared with that of the normotensive group and controls. Moreover, DLS was elevated in the low-renin group of essential hypertension, as compared with that of the normal/high-renin group or controls. The activity of DLS correlated positively with mean arterial pressure and negatively with plasma renin activity, but not with growth hormone levels.

IN CONCLUSION

an endogenous sodium pump inhibitor/digoxin-like substance may play a role in the pathogenesis of low-renin hypertension in acromegaly.