The effect of Na 2 SO 4 on urinary acidification in the intact fetal lamb

Recent studies have shown that the fetal kidney is limited in its ability to acidify the urine and to secrete hydrogen ions when compared to the adult kidney. To further study H+ secretion and the ability of the fetal kidney to establish a pH gradient between blood and urine, Na2SO4 was infused into the intact fetus. Studies were done on 7 near-term pregnant sheep and their fetal lambs. The ewes were injected with DOCA and the fetuses were given cortisone acetate. This served to enhance renal tubular reabsorption of Na+. Caesarean sections were performed and 75cc of 8% Na2SO4 was infused into each fetus. Blood and urine samples were collected from the ewe and fetus. There were no significant changes in fetal or maternal blood pressure, pulse, temperature or pCO2. The mean initial urine and blood pH in the fetus was 7.075 and 7.352 respectively. The mean minimum urine pH in the fetus after Na2SO4 was 5.2 with a range of 4.7–5.7. The mean minimum blood pH in the fetus after Na2SO4 was 7.362. The mean urine pH in the ewe before and after Na2SO4 was 5.824 and 5.920 respectively. This is consistent with little or no transfer of SO4 = across the placenta. The mean maximum TA and NH4 excretion in the fetus was 4.35 and 8.21 μEq/min/kg respectively. There was no correlation between fetal weight and response time before production of an acid urine. These studies indicate that in the intact fetal lamb, a stimulus (DOCA) to the fetal kidney to reabsorb Na+ without equivalent amount of anion results in intense acidification of the urine. The fetal kidney is thus able to establish a pH gradient with no evidence of intrinsic limitation of hydrogen ion secretion.