Renal clearance measurements of electrolytes in embryonic chickens.

Plasma ion concentrations and renal functions were examined in chick embryos after 9, 12, and 15 days of incubation. Plasma calcium and phosphate values rise steadily and significantly between days 9 and 15 of development. Values of other plasma ions (sodium, potassium, magnesium, sulfate) remain more or less the same during this developmental period. Glomerular filtration rates and urine flow rates decline steadily and significantly during this period of embryogenesis when expressed relative to body weight. Renal clearance values of calcium decrease between day 9 (16% of filtered calcium is excreted) and day 15 (4%). The latter value is the same as in birds after hatching and indicates that calcium is being conserved by the kidney of the chick during late embryogenesis. Other ions that appear to be conserved by the embryonic kidney are sodium and sulfate, whereas high percentages of filtered phosphate, potassium, and magnesium are excreted. Except for calcium, there was no significant difference between the renal handling of ions by the mesonephric kidney (functional in 9 day embryos) and the metanephric kidney (predominant in the 15 days embryos).