Regulation of Urine Osmolality in Fetal Sheep

Wintour, E. M.; Hennessy, D. P.; Congiu, M; Hardy, Kenneth J.

doi:10.1113/expphysiol.1982.sp002658

Cited by 44 publications

(32 citation statements)

References 24 publications

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“…The absence of an increase in GFR, with cortisol infusion, in the mature fetuses, in addition to a more effective distal tubular sodium reabsorption, may be responsible for the absence of a natriuretic response in the mature animal. The decrease in urine osmolality that occurs as fetuses mature also argues that distal mechanisms are more effective in NaCl reabsorption before term (32).…”

Section: Resultsmentioning

confidence: 99%

Gestational Changes in Renal Responsiveness to Cortisol in the Ovine Fetus

1989

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ABSTRACT. The ontogenetic renal responsiveness to exogenous cortisol was examined in the chronically cannulated ovine fetus. The contribution of effects a t proximal and distal tubule of the kidney were studied also. Cortisol (81.5 pg/h) was infused into immature ovine fetuses (mean gestational age -113.9 days) on five occasions and increased blood cortisol from 0.8 f 0.5 to 21.3 + 6.2 nmol/ liter. This dose of cortisol produced a highly significant diuresis and natriuresis, in part due to an increase in GFR and in part due to a significant decrease in proximal tubular reabsorption of sodium. Cortisol (107.2 + 4.7 &h) was infused into mature fetuses (mean gestational age 133.4 days) and produced an increase in blood cortisol concentration from 11.4 + 5.6 to 33.7 2 6.8 nmol/liter. No natriuresis or diuresis was seen in the mature fetuses. Cortisol caused a significant depression of proximal tubular sodium reabsorption in mature fetuses, but this extra load was reabsorbed in the distal tubule in these fetuses. The inability of the premature or very low birth wt baby to maintain normal sodium balance on a standard salt intake may be due, at least in part, to a "fetal" renal response to the high plasma cortisol concentrations found in such babies. As the kidney matures it becomes capable of increasing distal tubular sodium reabsorption to compensate for any increased distal tubular fluid delivery. (Pediatr Res 26: 6-10, 1989) Abbreviations FRN,, fractional reabsorption of sodium FR,,i, fractional reabsorption of lithium uN,,v, uKV, UclV, Uc.V, renal excretion rate of sodium/ potassium/chloride/calcium may be responsible for neonatal hyponatremia. However, subsequent investigations have shown that a characteristic of this defect is decreased proximal tubule reabsorption of sodium (2) implying that renal insensitivity to aldosterone may be only partially responsible. The relative immaturity of renal function in very low birth wt and premature neonates seems to be important in the pathogenesis of hyponatremia. Premature neonates exhibit a greater natriuresis and a lower GFR in response to oral salt loading when compared to full-term neonates (5, 6). This is consistent with histopathologic studies that show that glomerular formation in the human infant is not complete until late in gestation (7), whereas tubular development is not complete until 1 y after birth (8).In mature mammals the presence of adrenal steroids is essential for normal renal function. A characteristic of adrenalectomized or hypophysectomized animals and patients with adrenal or pituitary insufficiency is a delayed diuresis following oral or parenteral water loading, accompanied by impaired sodium conservation and reduced GFR and renal blood flow. Administration of deoxycortisone acetate or aldosterone in the presence of normal sodium balance and extra-cellular volume has no effect on the delayed diuresis, whereas cortisol-like steroids correct this diuresis (9-1 1).Clinical investigations have reported that premature neonates have higher plasma co...

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Section: Resultsmentioning

confidence: 99%

Gestational Changes in Renal Responsiveness to Cortisol in the Ovine Fetus

1989

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“…The two groups of animals studied were divided at 120 d gestation because there is evidence that fetuses younger than 120 d behave differently from fetuses older than 120 d both in their capacity to release ADH (Robillard et al 1981;Rose et al 1981) and the sensitivity of the fetal kidney to infused ADH (Wintour et al 1982).…”

Section: Discussionmentioning

confidence: 99%

Gestation‐dependent Aspects of the Response of the Ovine Fetus to the Osmotic Stress Induced by Maternal Water Deprivation

Bell¹,

Congiu²,

Hardy³

et al. 1984

Exp Physiol

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SUMMARYWater deprivation was produced in pregnant sheep by withholding water for 24 h and then giving them 500 ml/d for the subsequent 3 d. All ewes bore chronically cannulated fetuses. Eleven experiments were performed in group I animals (gestation periods of 107-119 d at maximal stress) and eight experiments in group II (126-144 d of gestation). Measurements were made of maternal and fetal plasma osmolalities, fetal urine flow rate and osmolality, amniotic fluid osmolality and fetal plasma antidiuretic hormone (ADH) concentration. The experimental protocol produced a larger increment in maternal and fetal plasma osmolalities in group I than in group II (P < 0 025). For group I fetuses the relationship between plasma ADH concentration, [ADH] and plasma osmolality was log [ADH] = -4-50+0-0174 (osmol) which was significantly different from that for group II fetuses, log [ADHI = -1046+0-0373 (osmol) (P < 0-02). Thus plasma [ADH] was significantly greater, at a given plasma osmolality, in older (group II) than younger (group I) fetuses. For a given value of fetal plasma [ADH] there was a greater reduction in fetal urine free water clearance in older than younger fetuses. Water deprivation of the ewe did disturb the composition of amniotic fluid and the trend in amniotic fluid osmolality followed the trend in fetal urinary osmolality.

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“…We have suggested previously that the renal function of the premature or growth-retarded neonate might resemble that of the fetus rather than that of the normal newborn, and shown that cortisol has a unique natriuretic effect in the immature ovine fetal kidney (5). The immature fetal kidney is less responsive to endogenous or exogenous AVP than is the kidney of the nearterm fetus (6,7). With the discovery of an endogenous natriuretic peptide of atrial origin (8,9) it seemed to be important to find out whether this peptide exerted any influence over sodium handling by the immature fetal kidney.…”

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confidence: 99%

Action of Atrial Natriuretic Peptide in the Immature Ovine Kidney

et al. 1987

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ABSTRACT. This study examines the effects of infused human atrial natriuretic peptide 1-28 (hANP) on ovine fetal renal function. hANP was infused into chronically cannulated ovine fetuses of 103-128 days gestation (term 142-152 days) at 1.1 (4), 2.2 (5), and 4.4 (5) ~g / h for 2 h. Isotonic saline was infused in 10 control experiments. The fractional reabsorption of infused lithium was used as a marker of proximal tubular sodium reabsorption. Glomerular filtration rate and urinary water and electrolyte excretion were assessed. The blood pressure and heart rate were unaltered by any dose of hANP. The lowest dose (1.1 pg/h) did not produce any significant changes in glomerular filtration rate, urinary electrolyte or water excretion, or fractional reabsorption of lithium. hANP, at 4.4 pg/h, caused a significant ( p < 0.001) 5-fold increase in the excretion of Na, Cl, and Ca, doubled the excretion rate of K and free water clearance, and significantly increased glomerular filtration rate. Fractional sodium reabsorption and fractional reabsorption of lithium were significantly decreased ( p < 0.001, < 0.01, respectively). The results show that the fetal kidney, at this stage, is as responsive to hANP as is the adult kidney. The natriuretic action of hANP is related to increases in glomerular filtration rate and proximal tubular rejection of sodium (as assessed by fractional reabsorption of lithium). The excessive salt loss of the premature or low birth weight neonate, which also involves increased delivery of filtrate to the distal tubule, may be due to endogenous hANP, circulating at high concentrations. (Pediatr Res 22: 11-15, 1987) Abbreviations hANP, human atrial natriuretic peptide 1-28 GFR, glomerular filtration rate FRN,, fractional reabsorption of sodium FRj,j, fractional reabsorption of lithium UN., K , c,, ca V, renal excretion rate of sodium/potassium/ chloride/calcium CIIzo, free water clearance AVP, arginine vasopressin C,.i, clearance of lithium MAP, mean arterial pressure HR, heart rate

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Regulation of Urine Osmolality in Fetal Sheep

Cited by 44 publications

References 24 publications

Gestational Changes in Renal Responsiveness to Cortisol in the Ovine Fetus

Gestational Changes in Renal Responsiveness to Cortisol in the Ovine Fetus

Gestation‐dependent Aspects of the Response of the Ovine Fetus to the Osmotic Stress Induced by Maternal Water Deprivation

Action of Atrial Natriuretic Peptide in the Immature Ovine Kidney

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