Figure 2.

Schematic to illustrate the complex control of fluid and sodium balance and the multiple ways in which estradiol (E₂) and progesterone (P₄) may influence these processes. Adapted with permission from Stachenfeld.²⁴ Fluid and sodium regulation are controlled by a number of complex systems, all of which are influenced by estrogens and progesterone. Both the central nervous system (CNS) and the peripheral nervous system (PNS) contribute to fluid regulation; estrogens and progesterones can influence fluid regulation directly via the brain or indirectly by influencing the actions of angtiotensin II (ANG II) and arginine vasopressin (AVP) blood pressure changes and changes in the sodium-regulating hormones (aldosterone and renin [RAAS]). Estradiol and P₄ can also increase brain ANG II mediated in the brain and increase this hormone’s important stimulating effect on thirst and fluid intake. Finally, both E₂ and P₄ influence sodium and water regulation in the distal tubules of the kidney. This impact can occur directly on the tubules or through both AVP and the RAAS and contribute to water retention.