Renal Hemodynamics and Functional Changes during the Transition from Fetal to Newborn Life in Sheep

Kt, Nakamura; Gp, Matherne; Oj, McWeeny; Fg, Smith; Je, Robillard

doi:10.1203/00006450-198703000-00003

Cited by 56 publications

(31 citation statements)

References 28 publications

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“…A rise in GFR after birth has also been reported by others (2,17). In the present study, we showed that a greater rise in GFR after birth correlated with a greater rise in diastolic pressure.…”

Section: Discussionsupporting

confidence: 91%

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Changes in Renal Function and Blood Volume in the Newborn Lamb Delivered by Cesarean Section

Gibson

Lumbers

1994

Pediatr Res

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To determine the cause of the transient natriuresis in lambs within 1-2 h of birth, renal function and blood volume (BV) were measured in nine chronically catheterized fetal sheep aged 139-145 d before and after delivery by cesarean section. After delivery, sodium excretion increased &fold. This was due to a transient rise in glomerular filtration rate (by 39 + 21%, p < 0.02) and a fall in fractional reabsorption of sodium by the proximal tubule from 63.4 2 2.5% to 53.4 + 3.4% @ < 0.01). The distal tubule failed to compensate fully for this fall, because fractional reabsorption by the distal tubule rose from 35.5 2 2.4% to only 41.6 2 2.2% @ < 0.05). The extent of the natriuresis did not depend on the lamb's initial BV per kg at birth. However, the amount of fluid excreted and the clearance of sodium during a 45-min period within the first 1-1.25 h after birth were approximately equal to the fall in BV that occurred during this time. Thus, most of the fall in After birth, human infants have a transient increase in urine flow rate (1). Similarly, lambs delivered by cesarean section at 139-145 d have a transient natriuresis and disruption of glomerulotubular balance (2). It has been suggested that volume expansion of the newborn, resulting from placental blood transfusion, may contribute to this diuresis (3). We postulated that lambs with larger BV relative to their weights would show a greater natriuresis than lambs with smaller BV per kg body weight. It should be noted that because it was not possible to measure partitioning of the fetal BV between the fetal body and the placenta before birth, it could not be determined whether placental transfusion occurred with delivery.

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Section: Discussionsupporting

confidence: 91%

“…However, even after cesarean section, lambs have elevated levels of ADH, plasma renin activity, AII, aldosterone, catecholamines, and atrial natriuretic peptide, particularly within the first hour (17,(21)(22)(23). In addition, cortisol levels increase toward the end of gestation (24).…”

Section: Discussionmentioning

confidence: 99%

Changes in Renal Function and Blood Volume in the Newborn Lamb Delivered by Cesarean Section

Gibson

Lumbers

1994

Pediatr Res

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“…After the fetal monitoring period, the pregnant ewe was brought back to the surgical suite, and the fetus was delivered by cesarean section performed under spinalepidural anesthesia using 10 mL of 1% lidocaine as previously described (24). Immediately after birth, the newborn lamb was dried and placed under an overhead infant radiant warmer to keep body temperature at 39°C.…”

Section: Methodsmentioning

confidence: 99%

“…Arterial blood (5 mL) REGULATION OF RENAL AT, GENE EXPRESSION 757 was collected at 1, 4, 8, and 24 h after birth. Newborn blood samples were replaced with blood collected from the fetal side of the placental circulation after the umbilical cord was cut at the time of the cesarean section, as previously described (24).…”

Section: Methodsmentioning

confidence: 99%

Ontogenic Changes and Regulation of Renal Angiotensin II Type 1 Receptor Gene Expression during Fetal and Newborn Life

et al. 1994

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Factors regulating the expression of the angiotensin I1 subtype 1 (AT,) receptor during fetal life have not been investigated previously. The present study was designed 1) to characterize the ontogeny of AT, receptor gene expression in the kidney of fetal and newborn sheep and 2) to determine the influence of both glucocorticoids and renal nerves in modulating AT, gene expression during fetal life and during the transition from fetal to newborn life. We first isolated and cloned a PCR product that has 98 and 94% homology with the cDNA encoding the bovine and pig AT, receptors, respectively, and 99 and 98% homology with the corresponding deduced protein sequences. Probing with this cDNA, we demonstrated that renal AT, mRNA expression did not change significantly during the last trimester of gestation in fetal sheep or immediately after birth but decreased significantly 10 d after birth. We also demonstrated that renal denervation in the fetus had no effect on renal AT, gene expression in 24-h-old newborn lambs. On the other hand, we observed in 130-d twin fetuses that a continuous intraperitoneal infusion (1 mL/h) of cortisol (3 mg/h or 6.2 p,mol/h) for 48 h in one of the twins increased the fetal plasma cortisol concentration from 32.0 + 7.1 to 1126 r 231 nmol/L and produced a significant decrease ( p < 0.005) in renal AT, gene expression compared with the control twin receiving an intraperitoneal infusion of 0.9% NaCl. In summary, this study demonstrates that renal AT, gene expression is elevated during fetal life and decreases after birth. It is also shown that glucocorticoids, but not renal nerves, contribute to the regulation of renal AT, gene expression during development. (Pediatr Res 36: 755-762, 1994)Abbreviations RAS, renin-angiotensin system AII, angiotensin I1 AT,, angiotensin I1 subtype 1 receptor AT,, angiotensin I1 subtype 2 receptor PCR, polymerase chain reaction RSNA, renal sympathetic nerve activity PRA, plasma renin activity rRNA, ribosomal RNA It has become apparent that the physiologic role of the RAS changes during embryonic and fetal maturation (1-4). Early during development, the RAS exerts a major influence o n cellular growth and organ differentiation (3-6). It is only later during fetal life that the RAS becomes an important modulator of blood pressure and distinct A11 receptor subtypes (AT, and AT,) (3, 9, 10). The AT, receptor subtype is expressed early during embryonic life in the rat (11,12), predominates in the fetal mesenchyme (3), and shows a marked decrease in expression during fetal and postnatal maturation (3). On the other hand, the AT, receptor subtype appears later during fetal development in the rat (3, 9, 10) and seems t o b e localized mainly in areas related t o blood pressure regulation and fluid homeostasis (3). Recent studies in rats have also shown that the AT, receptor gene is expressed in the fetal kidney, liver, adrenal, and heart and that the expression of this gene is developmentally regulated (9, lo), in agreement with previous A11 radioligand and in situ rece...

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“…Dexamethasone (5 mg) was given intramuscularly 12 h before starting the experiment to prevent respiratory distress after delivery by cesarean section, as previously described (13). Before delivery, each fetus received a continuous i.v.…”

Section: Materials a N D Methodsmentioning

confidence: 99%

Developmental Regulation of the α1B-Adrenoceptor in the Sheep Kidney

et al. 1993

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ABSTRACT. The expression of renal ale-adrenoceptor (alB-AR) mRNA was studied and contrasted with the expression of renal renin mRNA in fetal and newborn sheep. Fetal sheep between 90 and 91, 116 and 118, and 139 and 141 d gestation (term is 145 d gestation) as well as newborn lambs between 1 and 2 d old and 8 and 10 d old were studied (n = 3 for each age range). The role of the renal nerves in regulating changes in ale-AR gene expression was also investigated by measuring renal cortical ale-AR mRNA levels and receptor kd and maximum number of binding sites in 24-h-old lambs that were either denervated (n = 6) or sham-operated (n = 5) 3 d before birth. During development, renal aIB-AR mRNA levels show a marked increase in term fetuses; this increase persists into the first 2 d of life and is distinct from the developmental pattern seen for renal renin mRNA levels. Denervation of term fetuses does not alter the expression of renal a,B-AR mRNA in newborn lambs when compared with sham-operated controls but decreases significantly the expression of the renin gene (p < 0.05). These results suggest that the ale-AR gene is developmentally regulated in the kidney in a pattern distinct from that seen for renin. Furthermore, the renal nerves, which play an important role in the regulation of renin gene expression at the time of birth, do not appear to be an important factor in the regulation of the als-AR during the maturation from fetal to newborn life. (Pediatr Res 34: 124-1 28, 1993) Abbreviations UIB-AR, UIB-adrenoceptor GAPD, glyceraldehyde-3-phosphate dehydrogenase B, ., maximum number of binding sites Previous studies ( I ) have suggested that stimulation of aadrenoceptors modulates renal hemodynamics and fluid and electrolyte homeostasis during development. For example, the renal and vasoconstrictor response to intrarenal infusion of phenylephrine (2), an al-adrenoceptor agonist, or to low-frequency renal nerve stimulation (3, 4) is greater in the near-term sheep fetus than in the newborn lamb. Similarly, fetal and newborn sheep show a greater antinatriuretic response to renal al-adrenergic stimulation than do older animals (5). It has also been shown that renal nerves modulate the natriuretic response to volume expansion in fetal and newborn animals (6) and that renal denervation before birth increases renal sodium excretion in the immediate postnatal period (7). Furthermore, studies in sheep (8) have demonstrated that renal nl-adrenoceptor density (B,,,) and affinity (kd) are greater in near-term sheep fetuses than in I-wk-old lambs and older sheep, suggesting that the changing responses to renal nerve stimulation and cul-adrenoceptor stimulation observed during renal maturation may be due to changes in al-adrenoceptors.In an effort to elucidate further the mechanisms regulating the developmental changes in renal nl-adrenoceptors. the present study was designed to determine the ontogenic changes in R I B -AR mRNA expression in the sheep, because the ale-AR is the predominant nl-adrenoceptor in the sheep renal ...

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Renal Hemodynamics and Functional Changes during the Transition from Fetal to Newborn Life in Sheep

Cited by 56 publications

References 28 publications

Changes in Renal Function and Blood Volume in the Newborn Lamb Delivered by Cesarean Section

Changes in Renal Function and Blood Volume in the Newborn Lamb Delivered by Cesarean Section

Ontogenic Changes and Regulation of Renal Angiotensin II Type 1 Receptor Gene Expression during Fetal and Newborn Life

Developmental Regulation of the α1B-Adrenoceptor in the Sheep Kidney

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