Adaptive changes in single-nephron GFR, tubular morphology, and transport in a pregnant rat nephron: modeling and analysis.

Normal pregnancy is characterized by massive increases in plasma volume and electrolyte retention. Given that the kidneys regulate homeostasis of electrolytes and volume, the organ undergoes major adaptations in morphology, hemodynamics, and transport to achieve the volume and electrolyte retention required in pregnancy. These adaptations are complex, sometimes counterintuitive, and not fully understood. In addition, the demands of the developing fetus and placenta change throughout pregnancy. For example, during late pregnancy, K retention and thus enhanced renal K reabsorption are required despite many kaliuretic factors. The goal of this study was to unravel how known adaptive changes along the nephrons contribute to the ability of the kidney to meet volume and electrolyte requirements in mid and late pregnancy. We developed computational models of solute and water transport in the superficial nephron of the kidney of a rat in mid and late pregnancy. The midpregnant and late-pregnant rat superficial nephron models predicted that morphological adaptations and increased activity of Na/H exchanger 3 (NHE3) and epithelial Na channel are essential for the enhanced Na reabsorption observed during pregnancy. Model simulations showed that for sufficient K reabsorption, increased activity of H-K-ATPase and decreased K secretion along the distal segments is required in both mid and late pregnancy. The model results also suggested that certain known sex differences in renal transporter pattern (e.g., the higher NHE3 protein abundance but lower activity in the proximal tubules of virgin female rats compared with male rats) may serve to better prepare females for the increased transport demand in pregnancy. Normal pregnancy in mammals is generally characterized by massive changes in plasma volume and electrolyte retention. This study provides insights into how the volume and electrolyte requirement in different pregnancy stages are met by coordinated adaptive changes in the kidney. The model results also suggested that certain known sex differences in the renal transporter pattern may serve to better prepare females for the increased transport demand in pregnancy.