Renal function in adult and fetal sheep.
Renal function was studied in unanaesthetised fetal sheep aged 112-120 days, 126-132 days and in adult non-pregnant ewes. Fetal sheep of less than 120 days excreted more chloride (P less than 0.01) and had a higher urinary pH (P less than 0.05) and lower net acid excretion (P less than 0.01) than older fetuses. The reabsorption of both chloride and bicarbonate rose sharply between 112 and 116 days. Because the fractional reabsorption of the 2 major anions of the extracellular fluid (bicarbonate and chloride) show age dependent increases, it would seem that tubular function matures later relative to the filtered load. As well older fetuses depend more on their kidneys to maintain plasma bicarbonate levels. Fetal glomerular filtration rate (GFR) was lower (1.59 +/- 0.15 (SEM) ml/min per kg) than adult GFR (2.4 +/- 0.2 ml/min per kg, P less than 0.01). Fetal renal blood flow was significantly less (1.6 +/- 0.2 ml/min per g) than adult renal blood flow (P less than 0.001, 6.4 +/- 0.3 ml/min per g kidney). Therefore relative to the adult, the fetal kidneys are underperfused and the filtered load/unit body mass is less, thus their excretory capacity is limited. However, other differences in fetal renal function compared with the adult i.e. excretion of more dilute urine (P less than 0.01), higher rates of clearance of sodium (P less than 0.05) and phosphate and a lower rate of potassium excretion (P less than 0.001) may reflect the different dietary status of the adult animal compared with the fetus.
D000818:Animals; D002245:Carbon Dioxide / Q000097:blood; D004573:Electrolytes / Q000097:blood / Q000652:urine; D005260:Female; D005312:Fetal Blood / Q000032:analysis; D005333:Fetus / Q000502:physiology*; D005865:Gestational Age; D005919:Glomerular Filtration Rate; D007668:Kidney / Q000196:embryology / Q000502:physiology*; D010100:Oxygen / Q000097:blood; D010313:Partial Pressure; D011247:Pregnancy; D012756:Sheep / Q000502:physiology*
D004573:Electrolytes; D002245:Carbon Dioxide; D010100:Oxygen