Estradiol and progesterone effects on transcapillary fluid dynamics

Estradiol and progesterone and increase plasma volume (PV) and extracellular fluid (ECF). We tested the hypotheses that estradiol alters Starling forces acting on vessels to reduce vascular permeability to proteins, thereby reducing protein and fluid movement out of the vasculature and increasing PV; while progesterone alters Starling forces to promote increases in interstitial protein and fluid volume that ultimately increase ECF. We suppressed estrogens and progesterone with a gonadotropin releasing hormone antagonist (GnRHant) in 8 women (22±2 y) for 16 days; estradiol (2 x 0.1 mg/day patches) was added for days 4–16 (E) and progesterone (200 mg/day) was added for days 13–16 (E+P). We estimated PV (Evans Blue dye), and Starling forces [(hydrostatic and oncotic pressures of plasma (Pv, COPp) and interstitium (Pi, COPi), capillary filtration coefficient (CFC)] in the forearm on days 2 (GnRHant), 9 (E) and 16 (E+P). In E, P[E2] increased from 23±7 to 268±37 pg/ml, with no change in P[P] (2.1±1.0 to 1.3±0.4 ng/ml). In E+P, P [E] increased to 211±53 pg/ml and P [P] increased to 13.6±5.1 ng/ml, P<0.05). PV increased during E and E‐P (48.2±2.9, 49.0±3.0 and 53.9±3.5 for GnRHant, E, E+P respectively, P<0.05). Pv, Pi, COPp and CFC were unaffected by hormone treatments, but COPi was increased during E+P (P<0.05) leading to COPp‐COPi gradients (25.4±3.0, 21.3±5.1 and 19.1±1.9 for GnRHant, E, E+P respectively) favorable to fluid transport from the vascular into the interstitial space. This gradient may be a factor in the greater overall extracellular fluid expansion typically seen with E+P, but does not appear to be a factor in PV expansion during E alone.