Non-osmotic sodium storage in placental tissue in hypertensive and normotensive pregnancies

The existing idea about sodium handling in the body postulates that total body sodium is regulated by strict regulation of body fluid. However, recent studies suggest non-osmotic sodium (Na+) storage in the skin. Active Na+ storage independent of volume retention is thought to be facilitated by negatively charged, highly sulfated GAGs which are able to bind Na+ in an osmotically inactive manner and are abundantly expressed in the insterstitium of the skin. Research has shown that high sodium diet increases the non-osmotic Na+ content of the skin and is correlated with the synthesis of new glycosaminoglycans. Furthermore, research has shown that sodium storage in the skin possibly influences blood pressure regulation by mechanisms which involve the immune system. GAGS are also highly expressed in the placenta and are known to have anticoagulant, inflammatory and pro-antigenic properties. Moreover, in previous studies it was found that during PE the amount of GAGs expressed in placental tissue differed when compared to normotensive controls. We previously conducted a pilot experiment in which we found that the placenta may also act as a buffer for non-osmotic sodium storage. Besides we found that in late-onset pre-eclampsia the placenta possibly loses this function. However, this pilot experiment was subjected to several limitations. Therefore, in this prospective cohort study we aim to further investigate a possible role for the placenta as non-osmotic sodium buffer during pregnancy and differences in this ability between normotensive pregnancies and pregnancies complicated by a hypertensive disorder.

This study is designed as a multi-center study (OLVG + Amsterdam UMC – location AMC). After screening for eligibility and given informed consent, additional information will be collected by a questionnaire (printed version or EPIC). Prior to delivery blood plasma will be collected for additional measurements of plasma sodium, osmolality and GAG analysis. Additional information about the pregnancy, the delivery and the newborn will be extracted from the electronic patient file. After delivery the placenta is send to the pathology department of the hospital, where the placental tissue will be analyzed.

Like the skin, the placenta is a buffer for non-osmotic sodium storage and acts as an adaptive mechanism to deal with increased sodium. We postulate that pregnancies with a hypertensive disorder will differ in their amount of non-osmotic sodium storage when compared to normotensive pregnancies.

- Third trimester of pregnancy
- Postpartum