Abstract
Vasopressin in fetal plasma (VPp) has been shown to increase following mannitol infusion to the mother (Leake, R.D. et al, Pediatr. Res.13:841, 1979). It was suggested that this increase was related to the hyperosmolality and/or hypovolemia induced by transfer of water from fetus to mother. In order to examine the response of the fetal kidney to these changes, we studied six chronically instrumented fetal lambs 120-131 days gestation following infusion of mannitol to the mother. Mannitol infusion caused an increase in osmolality of maternal plasma from 298±3.1 to 311±2.0 mOsm/kg. In addition this treatment caused an increase in fetal VPp from 1.9 to 3.2 pg/ml and osmolality (OsMp) from 292±2.9 to 299±2.1 mOsm/kg (Mean ±S.E.). Following infusion there was also a fall in fetal urine output from 0.15±0.019 to 0.10±0.009 ml/kg min and a rise in urine osmolality from 140±8.6 to 183±13.2 mOsm/kg (p<0.01). These changes led to a significant decrease in solute free water clearance from 0.08±0.009 to 0.05±0.004 ml/kg min but not in osmolar clearance.
These studies indicate that: 1) Mannitol to the mother induces a rise in fetal OSMp, 2) the rise must be due to transfer of water to the mother rather than fetal diuresis and 3) the fetal kidney contributes to the preservation of fluid volume in response to hypovolemia. Furthermore these results raise the possibility that diuretics given during pregnancy may cause dehydration in the fetus.
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Daniel, S., Stark, R., Tropper, P. et al. CONTRIBUTION OF THE FETAL KIDNEY TO PRESERVATION OF FLUID VOLUME DURING HYPOVOLEMIA. Pediatr Res 18 (Suppl 4), 360 (1984). https://doi.org/10.1203/00006450-198404001-01605
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DOI: https://doi.org/10.1203/00006450-198404001-01605