The effect of the inhibition of prostaglandin synthesis on renal blood flow in fetal sheep

Indomethacin and arginine vasopressin interaction in the fetal kidney: a mechanism of oliguria

OBJECTIVE

Indomethacin has been shown to cause fetal oliguria in humans and animals. This study was designed to test the hypothesis that indomethacin-induced fetal oliguria is mediated through the renal action of arginine vasopressin.

STUDY DESIGN

Twenty-seven late-gestation (129 +/- 4 days [mean +/- SE]) chronically catheterized fetal sheep were studied. After a 1-hour control period fetal responses to indomethacin, 0.05 mg/kg given intravenously, followed by a 4-hour maintenance infusion (n = 9), were compared with an identical indomethacin infusion plus an arginine vasopressin V2-receptor antagonist (d[CH2]1(5), D-Phe2, Ile4,Arg8,Ala9)-VP (n = 8) or vehicle alone (n = 10). Fetal arterial and venous pressures, heart rate, and urinary flow were measured continuously.

RESULTS

Fetal urinary flow rate (p < 0.0001) and free water clearance (p = 0.004) fell in response to indomethacin alone, but the addition of the arginine vasopressin V2-receptor antagonist blocked indomethacin's oliguric and free water effect. Urinary osmolality and sodium increased in both indomethacin and indomethacin+arginine vasopressin V2-receptor antagonist groups compared with vehicle (p < 0.05). Fetal arterial pressure increased in response to indomethacin, and the addition of the arginine vasopressin V2-receptor antagonist potentiated this response (p = 0.007).

CONCLUSIONS

These results suggest that (1) fetal oliguria secondary to indomethacin is mediated through the stimulation of the renal arginine vasopressin V2-receptor and (2) prostaglandin synthesis inhibition may play a role in renal tubular sodium handling. In addition, the arginine vasopressin V2-receptor plays a role in ameliorating the hypertensive response to indomethacin. We speculate that indomethacin stimulates circulating arginine vasopressin levels and enhances peripheral arginine vasopressin effects in the fetus, resulting in oliguria and hypertension.

Fetal renal pulsed Doppler waveform in prolonged pregnancies

OBJECTIVE

Our purpose was to determine Doppler waveforms of the fetal human renal artery in prolonged pregnancy in the presence or absence of oligohydramnios.

STUDY DESIGN

Fifty patients at or after 40 weeks were studied. Ultrasonography was performed to determine the amniotic fluid index by the four-quadrants technique. Two groups of patients were obtained on the basis of the amniotic fluid index. Group 1 had an amniotic fluid index > 5 (normal) (n = 33); group 2 had amniotic fluid index < or = 5 (oligohydramnios) (n = 17). Umbilical artery and fetal renal pulsed Doppler waveforms were determined and analyzed. The fetal renal artery systolic-to-diastolic ratio of the two groups was compared.

RESULTS

Fetuses with a low amniotic fluid index had a significantly higher ratio. A significant negative correlation coefficient between amniotic fluid index and fetal renal systolic/diastolic ratio was found (r = -0.435 and p < 0.01).

CONCLUSIONS

In prolonged pregnancies there is a significant relationship between the amniotic fluid index and the fetal renal systolic/diastolic ratio. In pregnancies associated with oligohydramnios the systolic/diastolic ratio is significantly higher than in those with normal amniotic fluid volume. These data suggest that intrarenal flow in prolonged pregnancies complicated with oligohydramnios is significantly different.

Indomethacin-induced urinary flow rate reduction in the ovine fetus is associated with reduced free water clearance and elevated plasma arginine vasopressin levels

OBJECTIVE

The purpose of our study was to explore the urinary responses of the ovine fetus to indomethacin levels comparable with those used therapeutically in the human fetus.

STUDY DESIGN

After a 1-hour control period, chronically catheterized ovine fetuses between 125 and 139 days of gestation were given an intravenous bolus of indomethacin (0.05 mg/kg estimated fetal weight) followed by a 0.0025 mg/kg/min continuous infusion for 5 hours. The experimental group (n = 9) was compared with a vehicle-only infusion group (n = 10).

RESULTS

There was a sustained 55.7% +/- 9.5% (mean +/- SEM) decrease in urinary output by 2 hours of indomethacin infusion (p < 0.00001, analysis of variance). Urinary osmolality, potassium, and chloride concentrations underwent sustained increases during the infusion period (p < 0.005). Free water clearance decreased by 67.5% +/- 12.0% (p < 0.001). Fetal arterial pressure increased only transiently (p < 0.05), and increases in venous pressure (p = 0.013) and heart rate (p < 0.0001) were sustained. Fetal plasma arginine vasopressin concentration increased during indomethacin infusion (p < 0.05) and was correlated with the fall in urinary flow rate and free water clearance (p = 0.002). During vehicle infusion no significant changes were observed in any of the variables.

CONCLUSIONS

Our data indicate that the fetus undergoes antidiuresis when exposed to low levels of indomethacin and that the observed antidiuresis is mediated by a decrease in free water clearance. The reduction in free water clearance may be mediated by increases in plasma arginine vasopressin concentrations.

Urinary and cardiovascular responses to indomethacin infusion in the ovine fetus

OBJECTIVE

Our objective was to explore the urinary and cardiovascular responses of the near-term ovine fetus to plasma indomethacin levels similar to those in the human neonate undergoing indomethacin therapy.

STUDY DESIGN

Chronically catheterized ovine fetuses between 125 and 139 days of gestation were studied. After a 1-hour control period we gave a bolus of 0.35 mg/kg estimated fetal weight of indomethacin into a fetal vein, followed by a 0.017 mg/kg/min continuous infusion for 5 hours (n = 9). Results were compared with a vehicle-infusion-only group (n = 10).

RESULTS

During the first 3 hours of indomethacin infusion, fetal urinary output was increased by an average of 84.9% +/- 55.6% (analysis of variance, p less than 0.01). Urinary osmolality and sodium and chloride concentrations underwent sustained increases throughout the infusion period (p less than 0.001). Sodium excretion increased by 212% +/- 111% (p less than 0.05). Fetal arterial and venous pressures increased (p less than 0.001), and the change in urinary flow correlated positively with the change in arterial pressure (R = 0.55, p = 0.014). Fetal heart rate increased by 10% +/- 4% 1 hour after the bolus and remained elevated throughout the remainder of the infusion relative to vehicle-infused animals (p less than 0.001). Vehicle infusion had no effect on any fetal variable.

CONCLUSIONS

This study does not support the hypothesis that indomethacin acutely reduces urinary flow rate in the late-gestation ovine fetus. Further, the observed urinary flow increases may be mediated in part by a pressure diuresis.