Biomedical subjects

R D Leake

Publications and source records attributed to R D Leake.

At least 37 records · Page 2Linked to original sources

PubMed1989

Vasopressin levels and pediatric head trauma.

The syndrome of inappropriate secretion of antidiuretic hormone is associated with head trauma; however, there are no reports concerning vasopressin levels in pediatric patients with head trauma. Urine vasopressin in eight children (mean +/- SEM, age 7.5 +/- 1.6 years, range 1 to 15 years) was measured by radioimmunoassay during their hospitalization for head trauma. Urine vasopressin values for ten healthy children (mean age 5.4 +/- 1.3 years) and for eight children hospitalized for systemic antibiotic treatment of infections (age 5.9 +/- 1.8 years) also were obtained. Urine vasopressin, urine and serum sodium concentration and osmolality, urea nitrogen, creatinine, and fluid intake were measured within 24 hours of admission and daily for the following two days. For the first three days following head trauma, mean urine vasopressin levels in pediatric patients with head trauma were increased (P less than .05) compared with those of healthy children. Despite fluid restriction to 85% of maintenance level, 25% of patients with head trauma exhibited the clinical syndrome of inappropriate secretion of antidiuretic hormone (hyponatremia, increased urinary sodium, diminished serum osmolality, and urine osmolality greater than serum osmolality). Urine osmolality greater than 800 mosm/kg was associated with markedly increased urine vasopressin levels (200 to 1,650 pg/mL); children with this finding may be at particular risk for the syndrome of inappropriate secretion of anti-diuretic hormone without restrictive water intake.

Adolescent↗

PubMed1988

Ovine fetal and adult atrial natriuretic factor metabolism.

Studies were conducted to quantify ovine fetal and adult atrial natriuretic factor (ANF) metabolism. A total of 14 pregnant ewes with singleton fetuses were prepared with vascular catheters. In protocol 1, six fetuses (mean gestation, 131 +/- 1 days) received intravenous infusions of synthetic human ANF (hANF, 100 ng.min-1.kg-1) for 60 min. Mean basal fetal plasma ANF levels increased from 180 +/- 44 pg/ml to a steady-state level of 1,233 +/- 192 pg/ml. In protocol 2, five fetuses (mean gestation, 130 +/- 1 days) received successive 40-min infusions of hANF at 5, 25, and 100 ng.min-1.kg-1. Although basal fetal plasma ANF levels (522 +/- 135 pg/ml) were greater than those observed in protocol 1, fetal plasma ANF levels increased to 1,580 +/- 295 pg/ml at the highest infusion rate. In both protocols 1 and 2, basal fetal plasma ANF levels were three- to fourfold greater than maternal levels. The fetal plasma ANF clearance rates calculated from protocol 1 and from the 25- and 100-ng.min-1.kg-1 infusions from protocol 2 were similar (89 +/- 10, 120 +/- 31, and 116 +/- 38 ml.min-1.kg-1, respectively) and were combined to yield a mean estimated fetal plasma ANF clearance rate of 102 +/- 11 ml.min-1.kg-1. In protocol 3, adult plasma ANF levels increased from 137 +/- 36 to 4,142 +/- 776 pg/ml in response to ANF infusion at 200 ng.min-1.kg-1. The mean plasma ANF clearance rate calculated for the adult animals was 59 +/- 12 ml.min-1.kg-1.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Arginine vasotocin and a novel oxytocin-vasotocin-like material in plasma of human newborns.

Plasma of human adults contains an oxytocin, vasotocin-like (OT-VT) immunoreactive material that is estrogen responsive in both males and females and the levels of which are elevated during pregnancy. Although OT-VT is immunoreactive with an antiserum raised against synthetic arginine vasotocin (AVT), the elution profile of OT-VT by high-performance liquid chromatography (HPLC) is distinct from AVT, arginine vasopressin (AVP) or oxytocin (OT). Because the fetus is also exposed to high estrogen levels during pregnancy and AVT has been reported to be present in human fetal pituitaries, cord blood samples from 16 vaginally delivered human newborn infants were examined for evidence of OT-VT and AVT. Analysis of an extracted pool of cord blood plasma by HPLC revealed 4 peaks (I-IV) of AVT-like immunoreactivity. Peaks II and IV coeluted with synthetic AVP and OT, respectively, and were attributable to cross-reaction of the AVT antiserum with these peptides. Peak I was identified as AVT on the basis of its coelution with synthetic AVT. Peak III eluted in a manner identical with OT-VT. These results indicate that human newborn plasma contains at least three neurohypophysial peptides, AVP, OT and AVT. Additionally, newborn plasma contains an AVT-like immunoreactive material that is distinct from AVT, AVP and OT, but is identical with a novel OT-VT material observed in plasma of estrogen-primed adults. The physiological significance of AVT and OT-VT in newborn plasma remains to be determined.

Arginine Vasopressin↗

PubMed1988

Ovine fetal urine contribution to amniotic and allantoic compartments.

The ovine pregnancy has been extensively studied as a model for amniotic fluid metabolism potentially serving as a model for human oligohydramnios. However, it is recognized that the ovine pregnancy contains an allantoic fluid compartment not present in human pregnancies at term. Earlier studies in sheep suggested that the fetal urine contribution to allantoic fluid diminished at term, but without an explanation for maintenance of the significant volume of the allantoic cavity. In the present study we examined the relative fetal urine excretion of 3H-inulin into the allantoic and amniotic cavities in the near-term ovine pregnancy. Amniotic and allantoic volumes, as determined by technetium-labelled dextran and chromium-tagged erythrocyte dilution, were similar although there were significant differences in composition. The allantoic fluid compartment received an equal or greater proportion of fetal urine than did the amniotic fluid during the study period. These results indicate the importance of the allantoic fluid volume and composition in the study of ovine fluid dynamics.

Allantois↗

PubMed1988

Fetal atrial natriuretic factor and arginine vasopressin responses to hyperosmolality and hypervolemia.

Atrial natriuretic factor (ANF) is a class of diuretic and natriuretic peptides secreted by mammalian cardiac atria. Although basal plasma ANF levels in the ovine fetus are elevated relative to the adult, fetal secretion of ANF increases in response to intravascular isotonic saline infusion. Recent in vitro and in vivo studies indicate that ANF secretion also may be stimulated by increased plasma osmolality and/or sodium concentration. The present studies were conducted to determine if volume expansion associated with increased plasma osmolality would further augment ANF secretion in the ovine fetus. In response to successive 30-min intravenous infusions of 3% saline at 0.5 and 1.0 ml/kg/min fetal plasma ANF significantly increased from a basal level of 98 +/- 31 pg/ml to a peak of 439 +/- 42 pg/ml (p less than 0.05). During a 30-min postinfusion recovery period, fetal plasma ANF significantly decreased from peak values to 224 +/- 10 pg/ml (p less than 0.05), although remaining above basal levels. Fetal plasma osmolality significantly increased from 300 +/- 2 mosmol to 325 +/- 3 mosmol (p less than 0.05) whereas fetal plasma arginine vasopressin increased from 1.9 +/- 0.4 to 10.9 +/- 7.0 pg/ml (p less than 0.05) at the conclusion of the 3% saline infusion. During the saline infusion a significant increase in fetal heart rate and decrease in fetal hematocrit were noted. Fetal blood pressure and maternal plasma ANF and arginine vasopressin concentrations remained unchanged. Despite the potential stimulatory effects of hyperosmolality, increased plasma arginine vasopressin, and intravascular volume expansion, the increase in fetal plasma ANF in the present study did not exceed that induced by isotonic saline alone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Atrial natriuretic peptide in the sheep.

To study atrial natriuretic peptide (ANP) physiology in the chronically catheterized pregnant sheep model we developed a heterologous radioimmunoassay for ovine ANP using an antiserum raised against 1-28 human ANP. This antiserum (Tor I) is specific for the aminoterminus of the human ANP molecule and shows little cross reaction with any carboxyterminus ANP fragments. Ovine ANP immunoreactivity was characterized using this antiserum and a commercially available carboxyterminus ANP antiserum obtained from Peninsula Laboratories. Each antiserum detected 2 peaks of immunoreactivity in ovine atrial extracts chromatographed on a Biogel P-10 column. The minor peak migrated at a position close to 125I-human ANP whereas the major peak represented a larger molecular weight species of ANP. Examination of gel filtration eluates of ovine plasma extracts showed one immunoreactive ANP peak using the Tor I assay system and 2 peaks with the Peninsula Laboratories assay. Plasma immunoreactive ANP levels were determined in 9 sheep using both radioimmunoassay systems. Mean (+/- SEM) levels were similar using the Peninsula Laboratories and the Tor I assay systems (57 +/- 8 pg/ml versus 43 +/- 4 pg/ml, P greater than 0.05). Using the Tor I antiserum, fetal plasma immunoreactive ANP levels were found to be significantly higher than maternal levels (188 +/- 17 versus 48 +/- 8 pg/ml, P less than 0.01) whereas pregnant and nonpregnant adult sheep had similar plasma immunoreactive ANP levels (48 +/- 8 versus 43 +/- 4 pg/ml, P greater than 0.05). Disappearance curves of synthetic human ANP from the plasma of maternal and fetal sheep were assessed using both immunoassay systems and found to be similar.

Animals↗

PubMed1987

Plasma atrial natriuretic peptide response to volume expansion in the ovine fetus.

Atrial natriuretic peptide is a potent diuretic and vasorelaxant peptide secreted from the cardiac atria of adult mammals in response to increased intravascular volume. In sheep, fetal plasma levels of atrial natriuretic peptide are significantly greater than maternal levels, but the factors that control fetal release of atrial natriuretic peptide have not been defined. The present studies were conducted to determine whether the fetus responds to increased intravascular volume by atrial natriuretic peptide secretion. The mean (+/- standard error of the mean) atrial natriuretic peptide of basal fetal plasma (115 +/- 24 pg/ml) in chronically catheterized ovine fetuses (131 +/- 1 days' gestation) was significantly greater than atrial natriuretic peptide levels of basal maternal plasma (56 +/- 12 pg/ml). In response to successive 30-minute intravenous infusions of 0.9% saline solution at 0.5 and 1.0 ml/kg/min, fetal plasma atrial natriuretic peptide significantly increased to a maximum of 409 +/- 72 pg/ml during the high-dose saline infusion and returned to 234 +/- 83 pg/ml during a 30-minute recovery period. The increase in fetal plasma atrial natriuretic peptide was significantly correlated with the volume of saline solution infused (r = 0.68). During the saline infusion, a significant increase in fetal blood volume and heart rate was noted. Fetal blood pressure, maternal plasma levels of atrial natriuretic peptide, and fetal and maternal plasma osmolality remained unchanged. Despite elevated basal levels of plasma atrial natriuretic peptide, the third-trimester ovine fetus responds to increases in intravascular volume with a further increase in atrial natriuretic peptide secretion.

Animals↗

PubMed1987

Clonidine decreases plasma and cerebrospinal fluid arginine vasopressin but not oxytocin in humans.

To evaluate the alpha 2-noradrenergic regulation of arginine vasopressin (AVP) and oxytocin (OT) in normal humans, we measured the effect of the alpha 2-agonist clonidine on concentrations of these neuropeptides in both plasma and cerebrospinal fluid (CSF). Subjects underwent two lumbar puncture studies, one of which was performed 100 min after oral administration of 5 micrograms/kg clonidine. Plasma AVP and OT were measured at a single time point 10 min before lumbar puncture. Both plasma and CSF AVP were significantly lower in the clonidine condition than in the control (no drug) condition. Neither plasma nor CSF OT differed significantly between conditions. Our data confirm previous reports of alpha 2-noradrenergic inhibition of neurohypophyseal release of AVP into blood, and extend these findings to healthy human subjects. Our data also suggest that AVP appearance in CSF, presumably from extraneurohypophyseal vasopressinergic neurons, is regulated by an inhibitory alpha 2-noradrenergic mechanism.

Adult↗

PubMed1987

Fetal arginine vasopressin under basal and hypoosmolal conditions.

Blood samples (4 ml) for plasma arginine vasopressin (AVP) measurements were obtained at 3- to 4-hour intervals under basal conditions for 1-2 days from 5 date-bred ewes with chronic maternal and fetal vascular catheters. In addition, 6 chronically catheterized ewes were infused with 2 liters of 0.45% NaCl over 30 min. Fetal and maternal blood samples were obtained before and after the infusion period for measurement of plasma osmolality and AVP concentrations. In the first study, maternal and fetal plasma AVP levels correlated significantly (p less than 0.01, by linear regression analysis) under basal conditions. In the second study, baseline mean (+/- SEM) plasma osmolality was similar for pregnant ewes and fetuses (303 +/- 3.1 and 302 +/- 2.4 mosm/kg, respectively). There was a significant (each, p less than 0.01 by paired t test) decrease from baseline in maternal and fetal osmolality during the 30 min after completion of the hypotonic saline (to 292 +/- 4.7 and 296 +/- 2.4 mosm/kg, respectively). Fetal plasma AVP levels decreased 17 +/- 6% by 30 min following the completion of water loading (1.7 +/- 0.07 to 1.4 +/- 0.16 microU/ml; p less than 0.05). Maternal plasma AVP levels decreased 16 +/- 4% by 30 min after completion of infusion (1.6 +/- 0.14 to 1.38 +/- 0.6 microU/ml; p less than 0.05). These results indicate that maternal and fetal plasma AVP levels correlate under basal conditions and that maternal water loading, which significantly decreases fetal plasma osmolality, significantly suppresses fetal plasma AVP concentrations.

Animals↗

PubMed1987

Tocopherol efficacy and safety for preventing retinopathy of prematurity: a randomized, controlled, double-masked trial.

To test the efficacy and safety of vitamin E in preventing retinopathy of prematurity, 287 infants with birth weights of less than 1.5 kg or gestational ages of less than 33 weeks were enrolled within 24 hours of birth in a randomized, double-masked trial of IV, followed by oral, placebo v tocopherol (adjusted to plasma levels of 3 to 3.5 mg/dL). In the 196 infants completing ophthalmic follow-up, tocopherol did not prevent retinopathy of prematurity of any stage (28% placebo treated v 26% tocopherol treated) or moderately severe retinopathy of prematurity (8% placebo treated v 11% tocopherol treated). Cicatricial sequelae were not significantly different (1/97 placebo treated v 3/99 tocopherol treated), with one placebo-treated infant and one tocopherol-treated infant having retinal detachments. Among all 232 infants examined, those treated with tocopherol had more retinal hemorrhage than placebo-treated infants (8/121 placebo treated v 16/111 tocopherol treated), and retinal hemorrhage correlated positively (P less than .01) with plasma levels of tocopherol after the first 2 weeks of age. Prospective monitoring of morbidity including late-onset sepsis, necrotizing enterocolitis, etc revealed no differences between groups except that grades 3 and 4 intraventricular hemorrhage occurred more frequently in infants weighing less than 1 kg at birth who had received tocopherol (14/42, 33%) v those who had received placebo (4/43, 9%) (P less than .02). Our data do not support the use of tocopherol for prophylaxis against retinopathy of prematurity in premature infants and suggest that IV tocopherol treatment starting on day 1 may increase the incidence of hemorrhagic complications of prematurity, particularly in infants with birth weights of less than 1 kg.

Birth Weight↗

PubMed1986

Diurnal variations in plasma arginine vasotocin (AVT) concentrations in the ovine fetus.

Previously we have demonstrated the presence of AVT in the blood of fetal sheep. The source is not clear, but AVT has been identified in fetal pineal and pituitary glands. In view of the circadian secretory pattern of the pineal gland, we questioned whether fetal plasma AVT levels might vary diurnally. Plasma samples from five chronically catheterized ovine maternal ewes and fetal lambs 129-135 days' gestation were obtained at 3-19 hourly intervals for 1-2 days (mean +/- S.E.M. = 35 +/- 6 hours. Plasma AVT levels were determined by radioimmunoassay. Results were analyzed by nonlinear curve fitting procedures to relate hormone levels with time of day. Plasma AVT values for maternal ewes did not vary during the day in response to light/dark periods. The curve for mean fetal plasma AVT plotted against time showed oscillations with a period of about 25 hours (p less than 0.05). Peak fetal AVT levels were observed at 1600 hours and minimal levels at 0400 hours. These results indicate that ovine fetal AVT secretion varies diurnally. The site of AVT secretion may be the pineal gland; however, confirmation of this and identification of the physiological stimuli for secretion of fetal plasma AVT require further information.

Animals↗

PubMed1986

Renal effects of ovine fetal arginine vasopressin secretion in response to maternal hyperosmolality.

Acute increases in maternal plasma osmolality can increase amniotic fluid osmolality. Amniotic fluid is primarily derived from fetal urine production, and arginine vasopressin infusion can affect both fetal urine production and amniotic fluid osmolality. To assess the effect of short-term changes in maternal osmolality on fetal arginine vasopressin secretion and renal function, six ewes of 126 +/- 1 days' gestation received intravenous infusions of 20% mannitol (500 ml/10 min). In response to mannitol infusion, both maternal and fetal plasma osmolality increased significantly (302 +/- 3 to 326 +/- 2 and 300 +/- 1 to 309 +/- 2 mosm, respectively). Increased fetal plasma and urine arginine vasopressin concentrations were associated with significant increases in fetal urine osmolality (146 +/- 12 to 262 +/- 30 mosm) and sodium concentration (35.8 +/- 2.8 to 76.5 +/- 20 mu Eq/ml), but fetal urine production rates did not change (0.68 +/- 0.11 to 0.62 +/- 0.15 ml/min). These conclusions were reached: Acute increases in maternal osmolality can affect fetal arginine vasopressin secretion; arginine vasopressin-induced increases in fetal urine osmolality may contribute to increased amniotic fluid osmolality in response to maternal hyperosmolality.

Amniotic Fluid↗

PubMed1986

The plasma of pregnant women contains a novel oxytocin-vasotocin-like peptide.

Basal levels of immunoreactive oxytocin (OT) were measured in plasma of healthy pregnant women using two antisera to OT, Pitt Ab-1 and Pitt Ab-2, and an antiserum to arginine vasotocin, Tor AVT Ab. The mean (+/- SEM) level of immunoreactive OT Pitt Ab-1 was significantly higher, 7.7 +/- 0.9 microU/mL, than immunoreactive OT Pitt Ab-2, 0.9 +/- 0.2 microU/mL, P less than .001 measured in the same samples. AVT immunoreactivity in plasma of nonpregnant individuals was 0.8 +/- 0.16 pg/mL and in plasma of women in late pregnancy was 5.0 +/- 0.4 pg/mL. In four pregnant women receiving an infusion of synthetic OT (Pitocin, Parke-Davis, Morris Plains, NJ) a linear correlation was found between the dose of OT infused and the concentration of OT in plasma in samples measured with Pitt Ab-2, but no correlation was found in the same samples measured with Pitt Ab-1. Immunoreactive OT Pitt Ab-1 in plasma was not destroyed by a 60-minute incubation with pregnancy plasma. Pooled plasma from pregnant women was separated by reverse phase high pressure liquid chromatography (HPLC). OT Pitt Ab-1 and Tor AVT immunoreactivities in pregnancy plasma eluted in a position separate from synthetic OT. The differences found in levels of immunoreactive OT in the same samples of plasma measured with two antisera to OT illustrate an important reason why levels of OT in pregnant women may be reported to be variable among laboratories.

Chromatography, High Pressure Liquid↗

PubMed1986

Breast stimulation contraction stress test: uterine contractions in the absence of oxytocin release.

The contraction stress test has been widely used to manage high-risk pregnancies. Breast-stimulated uterine contractions have been assumed to be mediated through oxytocin release. We studied 20 women undergoing a breast-stimulated contraction stress test. There was no significant increase in plasma oxytocin levels during this study in either test responders or nonresponders. These results suggest that the presence of a breast stimulation-uterine contraction reflex is not mediated by oxytocin.

Breast↗

PubMed1986

Fetal recirculation of amniotic fluid arginine vasopressin.

Amniotic fluid volume reflects a balance between fetal lung fluid and fetal urine production and fluid reabsorption via fetal swallowing. Arginine vasopressin (AVP) infusion decreases both fetal lung fluid and urine production and increases amniotic fluid osmolality and AVP concentration. In the present study we assessed the effect of amniotic fluid AVP injection on plasma AVP (n = 6) and renal function (n = 4) in chronically catheterized fetal lambs (X gestation = 130 days). Thirty minutes after addition of 25 micrograms of synthetic AVP into the amniotic cavity, mean +/- SE fetal plasma AVP increased from a base line of 2.7 +/- 0.2 to 14.6 +/- 3.4 pg/ml (P less than 0.01). One hundred and twenty minutes after injection, plasma AVP had increased to 26.9 +/- 5.7 pg/ml. Fetal urine volume did not change (0.78 +/- 0.01 ml/min) but significant increases in urine osmolality (169 +/- 19 to 315 +/- 25 mosm) and urine sodium (64 +/- 11 to 125 +/- 11 mueq/ml) were observed 120 min after AVP administration. In conclusion, amniotic fluid AVP levels can affect fetal plasma AVP concentration, and AVP absorbed from the amniotic fluid by the fetus remains biologically active.

Amniotic Fluid↗

PubMed1986

Isovolemic hypotension in ovine fetus: plasma arginine vasopressin response and urinary effects.

Chronically prepared third trimester fetal lambs were administered intravenous infusions of nitropruside. Mean basal systolic and diastolic blood pressure (59.8 and 42.4 mmHg, respectively) decreased significantly during the infusion (49.2 and 36.8 mmHg, respectively) and increased significantly during the recovery period (66.4 and 48.5 mmHg, respectively). Fetal plasma arginine vasopressin (AVP) significantly increased from a mean basal level of 1.25 +/- 0.09 to 6.81 +/- 0.39 pg/ml during the hypotensive period. Urinary AVP basal levels of 1.21 +/- 0.13 pg/ml increased to 3.18 +/- 0.66 pg/ml during the hypotensive period and 5.87 +/- 0.82 pg/ml during the recovery period (P less than 0.05). The fetal urinary response to nitroprusside appeared biphasic. The hypotensive phase was marked by decreases in both free water and osmolar clearances. During the recovery phase free water clearance remained decreased, while osmolar clearance returned to basal levels. Thus AVP secretion represents an important mechanism for ovine fetal modulation of solute and water excretion in response to utero hypotensive stress.

Animals↗

PubMed1986

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

Animals↗

PubMed1986

Changes in steady state plasma arginine vasotocin levels affect ovine fetal renal and cardiovascular function.

The neuropeptides arginine vasopressin (AVP) and arginine vasotocin (AVT) are present in ovine fetal plasma in similar concentrations. Although AVP appears to be an important factor in the regulation of fetal water metabolism, the significance of AVT in the fetus is not clear. In the present study we assessed the effects of changes in steady plasma AVT levels on renal and cardiovascular function of fetal lambs (mean gestation, 128 days) maintained with vascular and bladder catheters. Successive 1-h infusions of synthetic AVT (n = 8) at rates of 1.0 and 2.0 ng/min X kg resulted in steady state plasma AVT levels of 30 +/- 7 and 59 +/- 12 pg/ml, respectively. The AVT infusions increased both urinary AVT concentrations and urinary AVT excretion. Plasma and urinary AVT clearance rates (45 +/- 8.4 ml/min X kg and 0.38 +/- 0.13 ml/min, respectively) remained constant over the observed range of plasma AVT levels. Urinary AVT clearance accounted for less than 1% of the total plasma AVT clearance and was nonsaturable. Increases in plasma AVT augmented urinary osmolar excretion and osmolar clearance, and evoked a significant natriuresis. AVT at either 1 or 2 ng/min X kg decreased fetal heart rate and tended to increase blood pressure. These results suggest that AVT, like AVP, may be important in modulating ovine fetal electrolyte homeostasis.

Animals↗