Abstract
The renal clearance of phosphate (P) was studied in 4 groups of fetal lambs. In group I, acute extracellular fluid (ECF) expansion was done in 4 fetuses by infusing Ringer's lactate without Ca++. In group II, ECF expansion with added Ca++ was done in 3 animals. In group III, the effect of exogenous bovine parathyroid harmone (PTH) was studied in 5 fetuses. In group IV, the response to endogenous fetal PTH was studied by infusing EDTA into 5 fetuses to produce hypocalcemia. In group I, plasma Ca++ (PCa) decreased by 10%. Fractional clearance of P (FCp) increased 3-fold (P<.001). P excretion factored by sodium clearance (EP/CNa) did not change. in group II, PCa did not change. FCp however, increased 2-fold (P<.01) while Ep/CNa again did not change. Plasma levels of immunoreactive PTH (iPTH) remained stable in groups I and II. in group III, tubular reabsorption of P decreased from a mean control of 96 to 78% and FCP increased 3-fold (P<.001). In group IV, PCa++ fell from a mean control of 12.8 to 5.6 mgm/dl. Plasma iPTH increased from 0.071 to 0.723 ng/dl. FCP increased 10-fold (P<.001) and P excretion increased independent of CNa (P>.05). These studies demonstrate that acute ECF expansion in the fetus results in an increased FCP independent of PCa++ and iPTH but related to CNa. Fetal hypbcalcemia stimulates production of fetal PTH and the fetal renal tubule is responsive to endogenous as well as exogenous PTH.
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Moore, E., Chung, E., Cevallos, E. et al. RENAL PHOSPHATE CLEARANCE IN FETAL LAMBS. Pediatr Res 11, 554 (1977). https://doi.org/10.1203/00006450-197704000-01108
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DOI: https://doi.org/10.1203/00006450-197704000-01108