Mechanism of volume adaptation in the awake early pregnant rat

Research was conducted to find out whether the increase in plasma volume (PV) during pregnancy is caused by fluid retention or by a shift within the extracellular fluid volume (ECFV) from the interstitium toward the intravascular compartment. Total body water, ECFV and PV together with the hematocrit and plasma osmolality 4, 8 and 12 postsurgery in chronically instrumented pregnant and nonpregnant rats were measured. Results showed that the increased PV during pregnancy is due to fluid retention rather than ECFV.