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 the pregnancy. For example, during late pregnancy, K+ retention and thus enhanced renal K+ reabsorption is required despite many kaliuretic factors. The goal of this study is 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 mid-pregnant and late-pregnant rat superficial nephron models predict that morphological adaptations and increased activity of the sodium hydrogen exchanger 3 (NHE3) and epithelial sodium channel (ENaC) are essential for enhanced Na+ reabsorption observed during pregnancy. Model simulations showed that for sufficient K+ reabsorption, increased H +-K +-ATPase activity and decreased K+ secretion along the distal segments is required in both mid- and late-pregnancy. Furthermore, 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 to male) may serve to better prepare the female for the increased transport demand in pregnancy.

Performance and Stability of Carbonate Fuel Cell Electrodes

Polarization studies and post analysis have been carried out for characterizing the electrochemical performance and processes affecting life and stability of carbonate fuel cell electrodes. Based on this understanding optimized electrodes design and new electrolyte composition were developed to improve cell performance and achieve the useful life of >5 years. The anode performance and stability were improved by developing an optimized microstructure with better electrolyte retention capabilities. Tests with an advanced electrolyte composition showed 25 mV improvement at 650°C and more than 45 mV at low temperatures compared to baseline. The NiO dissolution in advanced electrolyte is reduced by >60% compared to baseline electrolyte. Anode and cathode electrodes showed stable mechanical strength and stable electrochemical performance.

Vasopressin contamination as a cause of some apparent renal actions of prolactin

The injection or infusion of NIAMDD prolactin (NIH P-S-10) into unanesthetized rats resulted in water and electrolyte retention with a large increase in urine osmolality but no effect on glomerular filtration rate. Since these effects on urine output were also observed in homozygous Brattleboro rats, the antidiuretic activity could not have been caused by the release of endogenous antidiuretic hormone.Radioimmunoassay of NIH prolactin showed that it was contaminated with vasopressin (20 ng/mg of prolactin). By comparison, Sigma prolactin had no observed effect on urine excretion and contained very little vasopressin (2.5 ng/mg).It is concluded that some of the renal effects of prolactin that have been reported in the literature may have been caused by the contaminating vasopressin.

Body fluids and electrolytes after prolonged cardiopulmonary bypass

Fluid and electrolyte balance was studied in 21 dogs after partial heart-lung bypass of 10 hr duration. Water retention was demonstrated by an increase in body weight and total body water, primarily due to an increase in extracellular fluid. Electrolyte retention was suggested by an increase in total extracellular sodium, potassium, and chloride. Urinary output was relatively normal but a progressive drop in urinary specific gravity was observed during bypass. Blood pH remained essentially unchanged. However, an increase in plasma lactate and a decrease in plasma bicarbonate suggested some degree of hypoxia and metabolic acidosis at the cellular level. Altered hormonal regulation of sodium and water excretion, hemolysis secondary to blood trauma, and the exchange of intracellular potassium for extracellular hydrogen ions were considered possible explanation for the fluid and electrolyte changes observed. assisted circulation; heart-lung bypass; acid-base balance; fluid balance; extracorporeal circulation; electrolyte changes with partial bypass; membrane oxygenator; disc oxygenator; bubble oxygenator Submitted on June 20, 1963