Ovine fetal swallowing and renal responses to oligohydramnios

1994 ◽  
Vol 266 (3) ◽  
pp. R972-R978 ◽  
Author(s):  
L. K. Kullama ◽  
C. L. Agnew ◽  
L. Day ◽  
M. G. Ervin ◽  
M. G. Ross
Keyword(s):  
Amniotic Fluid ◽  
Volume Regulation ◽  
Urine Osmolality ◽  
Urine Flow ◽  
Fetal Urine ◽  
Chloride Excretion ◽  
Fluid Production ◽  
Ovine Fetus ◽  
Ovine Fetal ◽  
Renal Responses

Amniotic fluid (AF) volume regulation is dependent on a balance between fluid production and fluid resorption. We examined the effects of reduced AF volume on AF production by fetal urine and resorption by fetal swallowing and the response of these parameters to AF volume replacement. Eight time-dated pregnant ewes (125 +/- 1 days gestation) were studied before (day 1) and after (day 3) AF and fetal urine drainage. Drainage resulted in a significant decrease in AF volume (415 +/- 89 to 157 +/- 36 ml). Fetal urine osmolality increased (139 +/- 10 to 286 +/- 33 mosmol/kgH2O), while urine flow did not change significantly (0.31 +/- 0.04 to 0.23 +/- 0.06 ml/min), resulting in nonsignificant increases in osmolar, sodium, and chloride excretions. Fetal electromyographic swallowing activity decreased 30% (1.0 +/- 0.1 to 0.7 +/- 0.1 swallows/min; P < 0.05), while net esophageal flow decreased 74% (0.31 +/- 0.12 to 0.07 +/- 0.04 ml/min; P < 0.05). On day 4, 0.15 M NaCl (500 ml; 37 degrees C) was administered into the AF over 30 min. During the 2 h after reinfusion, urine flow (0.29 +/- 0.07 to 0.40 +/- 0.09 ml/min) and osmolar sodium and chloride excretion significantly increased, though fetal swallowing activity and esophageal flow did not change. Thus the ovine fetus responded to reduced AF volume by maintaining AF production and decreasing AF resorption. In response to AF replacement, urine flow increased while fetal swallowing activity did not change, consistent with an intramembranous pathway for fetal AF resorption.

Renal function in the chronically cannulated fetal llama: comparison with studies in the ovine fetus

1995 ◽  
Vol 7 (5) ◽  
pp. 1311 ◽  
Author(s):  
EM Wintour ◽  
R Riquelme ◽  
C Gaete ◽  
C Rabasa ◽  
E Sanhueza ◽  
...  
Keyword(s):  
Amniotic Fluid ◽  
Flow Rate ◽  
Urine Flow ◽  
Urine Flow Rate ◽  
Fetal Kidney ◽  
Fetal Plasma ◽  
Post Surgery ◽  
Fetal Urine ◽  
Ovine Fetus ◽  
Ovine Fetal

Samples of maternal and fetal plasma, fetal urine, and amniotic fluid were collected from 8 chronically cannulated pregnant llamas, in the last third of gestation. The samples were obtained for up to 18 days post-surgery. Osmolality, sodium (Na), potassium (K), chloride (Cl), and urea were measured on 40 samples collected on days 1, 2, 3, 4-5, 6-7, 8-9, and 10-19. The osmolalities of maternal and fetal plasma, fetal urine and amniotic fluid, averaged over these 7 time periods, were, respectively, 312 +/- 2, 311 +/- 1, 484 +/- 14, and 317 +/- 1 mosmol kg-1. Values are given as mean +/- s.e. The major differences from fetal fluid values in the ovine fetus (from previously published values) were the higher osmolality and urea concentration of llama fetal urine. Urine flow rate measured in 6 fetuses, 4.5-6.5 kg body weight, was 5.8 +/- 0.4 mliter h-1; urea clearance rate was 55.5 +/- 11.8 mliter h-1. Glomerular filtration rate (GFR), measured with 51Cr-EDTA in 5 fetuses on 1-4 occasions, was 111.4 +/- 23.3 mliter h-1. Fractional reabsorptions (FR) of Na, K and Cl were 97.9 +/- 1, 75.9 +/- 13.5 and 97.7 +/- 0.4% respectively. The GFR (25 mliter kg-1 h-1) and urine flow rate (1 mL kg-1 h-1) were less than half and about one-tenth the respective values in ovine fetuses. As Na reabsorption is the major oxygen-consuming activity of the kidney, the llama fetal kidney requires only half the oxygen needed by the ovine fetal kidney to reabsorb the filtered sodium load. The reason for the formation of hypertonic, rather than hypotonic, urine in the fetal llama may be due to both greater morphological maturity of the kidney and the excretion of as yet unidentified osmotically active organic substances.

Ovine fetal adaptations to chronically reduced urine flow: preservation of amniotic fluid volume

1996 ◽  
Vol 81 (6) ◽  
pp. 2588-2594 ◽  
Author(s):  
Stephanie E. Mann ◽  
Mark J. M. Nijland ◽  
Michael G. Ross
Keyword(s):  
Amniotic Fluid ◽  
Plasma Osmolality ◽  
Urine Osmolality ◽  
Urine Flow ◽  
Fluid Volume ◽  
Fetal Plasma ◽  
Arterial Blood ◽  
Amniotic Fluid Volume ◽  
Fetal Urine ◽  
Ovine Fetal

Mann, Stephanie E., Mark J. M. Nijland, and Michael G. Ross.Ovine fetal adaptations to chronically reduced urine flow: preservation of amniotic fluid volume. J. Appl. Physiol. 81(6): 2588–2594, 1996.—Adequate amniotic fluid (AF) volume is maintained by a balance of fetal fluid production (lung liquid and urine) and resorption (swallowing and intramembranous flow). Because fetal urine is the principle source of AF, alterations in urine flow and composition directly impact AF dynamics. Intra-amniotic 1-desamino-8-d-arginine vasopressin (DDAVP) is rapidly absorbed into fetal plasma and induces a marked fetal urinary antidiuresis. To examine the effect of intra-amniotic- DDAVP-induced fetal urinary responses on AF volume and composition, six chronically prepared ewes with singleton fetuses (gestation 128 ± 2 days) were studied for 72 h after a single intra-amniotic DDAVP (50-μg) injection. After DDAVP, fetal urine osmolality significantly increased at 2 h (157 ± 13 to 253 ± 21 mosmol/kg) and remained elevated at 72 h (400 ± 13 mosmol/kg). Urinary sodium (33.0 ± 4.5 to 117.2 ± 9.7 meq/l) and chloride (26.0 ± 2.8 to 92.4 ± 8.1 meq/l) concentrations similarly increased. AF osmolality increased (285 ± 3 to 299 ± 4 mosmol/kgH2O), although there was no change in fetal plasma osmolality (294 ± 2 mosmol/kg). Despite a 50% reduction in fetal urine flow (0.12 ± 0.03 to 0.05 ± 0.02 ml ⋅ kg−1 ⋅ min−1at 2 h and 0.06 ± 0.01 ml ⋅ kg−1 ⋅ min−1after 72 h), AF volume did not change (693 ± 226 to 679 ± 214 ml). There were no changes in fetal arterial blood pressures, pH,[Formula: see text], or[Formula: see text] after DDAVP. We conclude the following. 1) Intra-amniotic DDAVP injection induces a prolonged decrease in fetal urine flow and increases in urine and AF osmolalities. 2) Despite decreased urine flow, AF volume does not change. We speculate that, in response to DDAVP-induced fetal oliguria, reversed intramembranous flow (from isotonic fetal plasma to hypertonic AF) preserves AF volume.

Continuous ovine fetal hemorrhage: sensitivity of plasma and urine arginine vasopressin response

1986 ◽  
Vol 251 (4) ◽  
pp. E464-E469 ◽  
Author(s):  
M. G. Ross ◽  
M. G. Ervin ◽  
R. D. Leake ◽  
J. A. Humme ◽  
D. A. Fisher
Keyword(s):  
Blood Volume ◽  
Arginine Vasopressin ◽  
Urine Volume ◽  
Urine Osmolality ◽  
Fetal Plasma ◽  
Equivalent Rate ◽  
Fetal Urine ◽  
Ovine Fetus ◽  
Ovine Fetal ◽  
Fetal Response

Intravascular hemorrhage of the ovine fetus is a potent stimulus for arginine vasopressin (AVP) secretion. However, the method (acute, continuous) and rate of blood withdrawal may influence the fetal response. To determine the hemorrhage threshold for AVP secretion in response to slow continuous hemorrhage, five chronically catheterized ovine fetuses were continuously hemorrhaged (0.6% blood vol/min) to 24-30% blood volume withdrawal. Immediately after hemorrhage fetal blood was reinfused at an equivalent rate. In addition to AVP measurements by radioimmunoassay, fetal urinary responses were monitored as an index of fetal AVP secretion. Significant increases in plasma AVP occurred during hemorrhage (1.0 +/- 0.1 to 8.0 +/- 2.0 pg/ml). The fetal plasma AVP-hemorrhage threshold, as defined by regression analysis, occurred at withdrawal of 13.0% blood volume. Fetal urine volume significantly decreased from a mean basal rate of 0.59 +/- 0.03 to 0.21 +/- 0.06 ml/min at the completion of hemorrhage. Urinary sodium, potassium, and osmolar excretion also significantly decreased at the completion of hemorrhage. Urinary AVP excretion, urine osmolality, sodium, and potassium concentrations did not change significantly during the hemorrhage period but increased significantly during the reinfusion period; the delay a result of renal and catheter dead space. Reinfusion of blood resulted in a return of plasma AVP to basal levels. These results define a threshold for AVP secretion and demonstrate significant urinary effects in response to slow continuous hemorrhage.

Fetal renal contribution to amniotic fluid osmolality during maternal hypertonicity

1986 ◽  
Vol 250 (2) ◽  
pp. R235-R239
Author(s):  
L. L. Woods
Keyword(s):  
Amniotic Fluid ◽  
Continuous Infusion ◽  
Arginine Vasopressin ◽  
Urine Osmolality ◽  
Uterine Wall ◽  
Urine Flow ◽  
Bulk Flow ◽  
Vasopressin Antagonist ◽  
Fetal Plasma ◽  
Fetal Urine

The contribution of fetal urine to the increase in amniotic fluid osmolality during maternal hypertonicity was studied in chronically catheterized sheep of 130-135 days gestation. Nine percent NaCl was injected simultaneously into fetal and maternal veins, followed by a continuous infusion into the maternal vein. Maternal and fetal plasma osmolalities rose by 15 +/- 1 (SE) and 13 +/- 1 mosmol/kg, respectively, and remained constant for 4 h. Fetal urine osmolality rose significantly from 188 +/- 31 to 277 +/- 32 mosmol/kg within 1 h and remained constant thereafter. Fetal urine flow rose transiently, fell to normal within 10 min, and averaged 70% of normal beyond 1 h. Amniotic fluid osmolality rose by 10.8 +/- 2.8 mosmol/kg over 4 h. Following hypertonic injection into three fetuses blocked by the arginine vasopressin antagonist d(CH2)5D-tyr(Et)VAVP, urine osmolality did not change, and amniotic fluid osmolality rose by 2.7 +/- 0.3 mosmol/kg. Thus it appears that the increase in amniotic fluid osmolality during maternal hypertonicity may be due largely to an increased fetal urine osmolality coupled with a decreased flow of fetal urine into the amniotic space, rather than to bulk flow of fluid across the membranes and uterine wall.

V1- and V2-receptor contributions to ovine fetal renal and cardiovascular responses to vasopressin

1992 ◽  
Vol 262 (4) ◽  
pp. R636-R643
Author(s):  
M. G. Ervin ◽  
M. G. Ross ◽  
R. D. Leake ◽  
D. A. Fisher
Keyword(s):  
Receptor Agonist ◽  
Urine Osmolality ◽  
Cardiovascular Responses ◽  
Urine Flow ◽  
Receptor Blockade ◽  
Fetal Life ◽  
Receptor Stimulation ◽  
V2 Receptor ◽  
Ovine Fetal ◽  
Renal Responses

To assess the contributions of arginine vasopressin (AVP) V1- and V2-receptors to the ovine fetal responses to AVP, we studied V2-receptor stimulation in the presence of V1-receptor blockade, and selective V2-receptor stimulation in chronically catheterized fetal lambs. AVP administration (20 ng/kg) to the saline infused fetuses (n = 8; 132 +/- 2 days) significantly increased mean arterial pressure (MAP; 45 +/- 2 to 53 +/- 4 mmHg) and urine osmolality (Uosm; 134 +/- 13 to 379 +/- 42 mosmol/kgH2O) and decreased heart rate (HR; 168 +/- 3 to 147 +/- 5 beats/min) and urine flow (V; 0.48 +/- 0.10 to 0.19 +/- 0.03 ml/min). V1-receptor antagonist infusion, [d(CH2)5,Tyr(Me)]AVP (n = 7; 134 +/- 1 days) had no effect on fetal MAP, Uosm, HR, or V. V1-receptor blockade abolished the MAP response to AVP without affecting the HR and urinary responses. In a second series of animals (n = 6; 131 +/- 1 days), selective V2-receptor agonist infusion [desmopressin (DDAVP)] had no effect on fetal MAP or HR while initial changes in V and Uosm were identical to the effects of AVP alone. Our results demonstrate clear discrimination of V1- and V2-receptor-mediated events in the fetal MAP and renal responses to AVP. Moreover, the HR response to AVP is not mediated by the population of V1-receptors blocked by [d(CH2)5,Tyr(Me)]AVP or V2-receptors stimulated by DDAVP, suggesting the presence of additional AVP receptor subclass(es) during fetal life.

Development of ingestive behavior

1998 ◽  
Vol 274 (4) ◽  
pp. R879-R893 ◽  
Author(s):  
Michael G. Ross ◽  
Mark J. M. Nijland
Keyword(s):  
Amniotic Fluid ◽  
Functional System ◽  
In Utero ◽  
Ingestive Behavior ◽  
Salt Appetite ◽  
Fetal Life ◽  
Ovine Fetus ◽  
Near Term ◽  
Ovine Fetal ◽  
In Utero Development

Swallowing represents a primary physiological function that provides for the ingestion of food and fluid. In precocial species, swallowing activity likely develops in utero to provide for a functional system during the neonatal period. The chronically instrumented ovine fetal preparation has provided the opportunity for recent advances in understanding the regulation of in utero swallowing activity. The near-term ovine fetus swallows fluid volumes (100–300 ml/kg) that are markedly greater, per body weight, than that of the adult (40–60 ml/kg). Spontaneous in utero swallowing and ingestive behavior contribute importantly to the regulation of amniotic fluid volume and composition, the acquisition and potential recirculation of solutes from the fetal environment, and the maturation of the fetal gastrointestinal tract. Fetal swallowing activity is influenced by fetal maturation, neurobehavioral state alterations, and the volume of amniotic fluid. Furthermore, intact dipsogenic mechanisms (osmolality, angiotensin II) have been demonstrated in the near-term ovine fetus. It remains unknown to what degree, if any, fetal swallowing may be influenced by nutrient appetite, salt appetite, or taste. Nevertheless, the development of dipsogenic and additional regulatory mechanisms for ingestive behavior occurs during fetal life and may be susceptible to changes in the pregnancy environment. This review describes what is currently known regarding the in utero development of ingestive behavior and the importance of this activity for fetal and perhaps ultimately adult fluid homeostasis.

Renal, hormonal, and cardiovascular responses to chronic angiotensin I infusion in the ovine fetus

1997 ◽  
Vol 272 (6) ◽  
pp. R1912-R1917 ◽  
Author(s):  
K. M. Moritz ◽  
K. Tangalakis ◽  
E. M. Wintour
Keyword(s):  
Plasma Concentrations ◽  
Allantoic Fluid ◽  
Cardiovascular Responses ◽  
Urine Flow ◽  
Angiotensin I ◽  
Fetal Sheep ◽  
Arterial Blood ◽  
Urine Production ◽  
Fetal Urine ◽  
Ovine Fetus

Long-term infusion of angiotensin I (ANG I) into the ovine fetus has been shown to cause excess accumulation of fetal fluid in the allantoic compartment. It was hypothesized that this resulted from sustained increases in fetal urine production, and the hormonal basis was examined. ANG I (6.7 micrograms/h, n = 6) or isotonic saline (n = 6) was infused for 3 days into chronically cannulated ovine fetuses (112-122 days of gestation). ANG I caused an immediate and progressive increase in mean arterial blood pressure (from 42 +/- 2 to 57 +/- 4 mmHg), increased urine flow rate (from 15 +/- 3 to 48 +/- 8 ml/h), and increased glomerular filtration rate (from 97 +/- 15 to 146 +/- 24 ml/h), without significant changes in fetal plasma concentrations of aldosterone, atrial natriuretic factor (ANF), adrenocorticotropin, or cortisol. There were substantial increases in sodium and chloride excretion, due to both increased fetal urine concentrations and fetal urine flow, without significant changes in urine osmolality (from 134 +/- 9 to 147 +/- 12 mosmol/kg water). There were no significant changes in any parameter in the saline-infused fetuses. Neither amniotic or allantoic fluid volume was significantly changed by ANG I infusion, but allantoic fluid Cl- concentration increased significantly. The conclusions are that ANG I caused a diuresis and natriuresis in the fetal sheep independent of changes in cortisol or ANF.

DDAVP-induced maternal hyposmolality increases ovine fetal urine flow

1995 ◽  
Vol 268 (2) ◽  
pp. R358-R365 ◽  
Author(s):  
M. J. Nijland ◽  
M. G. Ross ◽  
L. K. Kullama ◽  
K. Bradley ◽  
M. G. Ervin
Keyword(s):  
Tap Water ◽  
Control Period ◽  
Plasma Osmolality ◽  
Urine Osmolality ◽  
Maternal Plasma ◽  
Urine Flow ◽  
Fetal Plasma ◽  
Maternal Urine ◽  
Fetal Urine ◽  
Fluid Transfer

Fetal urine flow is influenced by fetal intravascular volume, glomerular filtration rate, tubular reabsorption, and fluid regulatory hormones. As maternal-to-fetal fluid transfer is dependent on hydrostatic and osmotic gradients, we postulated that a chronic decrease in maternal plasma osmolality would promote transplacental fluid transfer and increase fetal urine flow. Six pregnant ewes and singleton fetuses (131 +/- 2 days; term = 150 days) received bladder and hindlimb arterial and venous catheters. After 5 days, plasma and urine composition, urine flow rate (Uvol), and plasma arginine vasopressin (AVP) levels were measured during a 2-h control period. At 2 h, tap water (2 liter, 38 degrees C) was administered to the ewe. At 3 h, ewes received a 20-micrograms bolus of 1-desamino-[D-Arg8]vasopressin (DDAVP), followed by continuous infusion (4 micrograms/h). In response to water loading, maternal urine osmolality decreased (761 +/- 158 to 339 +/- 13 mosmol/kgH2O), and Uvol increased. After DDAVP, maternal urine osmolality increased (1,270 +/- 89 mosmol/kgH2O), and Uvol, hematocrit, plasma osmolality (304 +/- 1 to 284 +/- 4 mosmol/kgH2O), and protein concentration decreased. Five hours after maternal DDAVP infusion, fetal plasma osmolality decreased (300 +/- 1 to 281 +/- 3 mosmol/kgH2O), and Uvol increased (0.4 +/- 0.1 to 1.3 +/- 0.2 ml/min) and remained elevated at 24 h. There was no change in fetal plasma DDAVP (immunoreactive AVP) levels or fetal urine osmolality. Controlled changes in maternal plasma osmolality may prove useful in modulating fetal urine flow and, ultimately, amniotic fluid volume.

Role of arginine vasopressin in fetal renal response to hypertonicity

1986 ◽  
Vol 251 (1) ◽  
pp. F156-F163
Author(s):  
L. L. Woods ◽  
C. Y. Cheung ◽  
G. G. Power ◽  
R. A. Brace
Keyword(s):  
Renal Function ◽  
Arginine Vasopressin ◽  
Urine Osmolality ◽  
Maternal Blood ◽  
Urine Flow ◽  
Fetal Blood ◽  
Fetal Plasma ◽  
Fetal Urine ◽  
Sustained Increase

We studied the effects of hyperosmolality on fetal renal function and the role of arginine vasopressin (AVP) in these responses. NaCl (9%) was injected intravenously into chronically catheterized ewes and their fetuses, followed by a continuous infusion of 9% NaCl into the ewes. The fetuses were either normal, infused with AVP, or infused with an AVP antagonist. In normal fetuses NaCl injection caused fetal and maternal blood osmolalities to be elevated by 10-15 mosmol/kg for 4 h with no change in fetal blood volume; fetal plasma AVP rose 42%. Fetal arterial pressures rose transiently by 2-10 mmHg. Fetal urine flow rose transiently by 73% after NaCl injection and then averaged 27% below control after 1 h, whereas fetal urine osmolality increased from 188 +/- 31 to 282 +/- 33 mosmol/kg. In a second group of fetuses AVP infusion alone caused fetal urine osmolality to increase by 123 +/- 39 mosmol/kg and urine flow to fall 31%, whereas in a third group the antagonist alone had no effect on urine flow or osmolality. After hypertonic injection into fetuses infused with AVP or the antagonist, the transient changes were similar to those in normal fetuses. However, the sustained increase in urine osmolality and decrease in flow after hypertonic injection were abolished in AVP-infused and antagonist-infused fetuses. Thus it appears that the transient changes in fetal renal function after hypertonic injection are not AVP-induced and may be due to transient increases in arterial pressure, whereas the prolonged changes in urine flow and osmolality appear to be mediated by increases in fetal plasma AVP levels.

Intraamniotic deamino(D-Arg8)-vasopressin: Prolonged effects on ovine fetal urine flow and swallowing

1996 ◽  
Vol 174 (1) ◽  
pp. 78-84 ◽  
Author(s):  
Linda K. Kullama ◽  
Mark J.M. Nijland ◽  
M.Gore Ervin ◽  
Michael G. Ross
Keyword(s):  
Urine Flow ◽  
Fetal Urine ◽  
Ovine Fetal
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