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Daily rhythmicity of renal blood flow (RBF) and urine flow (UF) was studied in fetal sheep between 121-125 d of gestation. Fetal arterial blood pressure, heart rate, UF, and right RBF were measured continuously for 24-h periods in 10 sheep. Rhythmic variations during a 24-h period were found for all variables studied. The rhythms of arterial blood pressure and heart rate were highly correlated, whereas an inverse correlation was found between arterial blood pressure with RBF and between arterial blood pressure with UF. These findings indicate that fetal RBF is not blood pressure dependent. Furthermore, fetal UF appears not to be mediated by pressure-dependent diuresis.

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Recently we have shown that activation of inflammatory reaction and clotting can be found immediately after delivery in preterm lambs ventilated for respiratory distress syndrome (RDS). To investigate whether antenatal glucocorticoids would attenuate postnatal activation of the inflammatory reaction and clotting, we studied ventilated preterm lambs delivered by cesarean section, 24 h after antenatal administration of betamethasone or placebo. Blood was sampled before clamping the cord, 5, 10, and 15 min after delivery, and 2-hourly afterwards. Blood was used to determine oxygenation index, alveolar – arterial partial O₂ difference (AaDO₂), AP50 titer (see text), polymorphonuclear leukocytes (PMNs), β-glucuronidase, thrombin inhibition, activated partial thromboplastin time, and clot lysis time. Bronchoalveolar lavage fluid was sampled before clamping the cord and 30 min and 1, 2, 4, 6 and 8 h after delivery and was analyzed for elastase, thrombin, and protein. After removal of the lungs, static compliance and water content of the lungs were determined. We found that betamethasone-treated lambs had lower oxygenation index and AaDO₂ than controls. At birth, PMN levels were higher, and the β-glucuronidase level was lower after betamethasone treatment. PMNs and β-glucuronidase did not change in betamethasone-treated lambs, in contrast to controls. Thrombin inhibition, activated partial thromboplastin time, and clot lysis time did not change in betamethasone-treated lambs, in contrast to controls. In both groups, elastase and protein levels in bronchoalveolar lavage fluid increased; the thrombin level increased in controls. The static compliance was better, and the water content of the lung was lower in the betamethasone-treated lambs. We conclude that early systemic activation of inflammatory reaction and clotting in preterm lambs with RDS are attenuated by antenatal betamethasone administration. Whether this is a direct effect of betamethasone on the inflammatory reaction or a result of a reduced ventilatory support because of less severe RDS after antenatal betamethasone treatment remains to be elucidated.

The effect of sustained moderate hypoxia on renal blood flow and renal function was studied in the ovine fetus (123–129 days). The experiments consisted of 48 h of isocapnic hypoxia, not resulting in acidemia, but sufficient to produce redistribution of blood flow in favor of the brain at the expense of the carcass. Hypoxemia was induced by maternal nitrogen inhalation. Fetal arterial O2 saturation and arterial O2 pressure ([Formula: see text]) decreased from, respectively, 50.6 ± 3.0% and 17.2 ± 0.9 mmHg during control to 36.4 ± 2.7% and 13.4 ± 0.7 mmHg on the first and to 32.2 ± 2.2% and 12.4 ± 0.7 mmHg on the second day of hypoxemia. Fetal renal blood flow and urine production rate were continuously measured using ultrasonic flow transducers. Fetal renal blood flow increased during hypoxemia from 11.8 ± 1.6 to 15.6 ± 1.8 ml/min and remained elevated throughout the 48-h hypoxemia period ( P < 0.01). Renal blood flow was inversely correlated with fetal [Formula: see text]( r is −0.69, P < 0.0001). Fetal urine production rate, glomerular filtration rate, filtration factor, osmotic clearance, and free water clearance did not significantly change from control values during hypoxemia or recovery. We conclude that hypoxemia without acidemia results in an immediate and considerable increase in fetal renal blood flow, which remains elevated for the entire hypoxemic period.