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Biomedical subjects

D Polk

Publications and source records attributed to D Polk.

31 records · Page 2Linked to original sources
PubMed1995

Effects of fetal corticosteroid treatments on postnatal surfactant function in preterm lambs.

Effects of prenatal corticosteroid on the properties of surfactant have not previously been evaluated. A single ultrasound-guided fetal injection with 0.5 mg/kg betamethasone 48 h before delivery of preterm lambs at 134- to 135-days gestation improved oxygenation, lowered the ventilatory pressures required to maintain arterial PCO2 between 30 and 40 Torr and decreased the protein leak of albumin from the intravascular to the alveolar space. This dose of glucocorticoid did not alter surfactant-saturated phosphatidylcholine pool sizes in the airspaces of preterm lambs. However, the treatment changed the characteristics of the surfactant recovered from the ventilated preterm lambs. The in vitro conversion from heavy to light subtype surfactant decreased from 59% for the saline-treated lambs to 37% for the corticosteroid-treated lambs after 180 min of surface area cycling (P < 0.02). Surfactant from the corticosteroid-treated lambs also increased the dynamic compliance of preterm surfactant-deficient rabbits more than did surfactant from the saline-treated lambs (P < 0.05). Prenatal treatment of preterm lambs with betamethasone improved the functional characteristics of surfactant without significant effects on the alveolar surfactant pool sizes.

Animals↗
PubMed1994

Ontogeny and effects of exogenous surfactant treatment on SP-A, SP-B, and SP-C mRNA expression in rabbit lungs.

The aims of the present study were to first characterize the ontogeny of mRNAs encoding the principal surfactant proteins SP-A, SP-B, and SP-C in rabbit lung tissues, followed by an evaluation of the effect of exogenous surfactant administration on endogenous expression of mRNA levels. Lung tissues were collected from New Zealand White rabbits on days 19, 21, 24, 26, 28, 30 of gestation, 1 day and 10 days after birth, and as adults. SP-A, SP-B, and SP-C mRNAs were first detected on gestational days 26, 24, and 19, respectively. The specific levels of these mRNAs generally increased to gestational day 28 and decreased transiently on 1 day of life. Adult values remained lower than those noted at 30 days gestation. For the second study, 29-day-gestation preterm rabbits were given either one or two treatment doses of natural surfactant or an organic solvent extract of natural surfactant, and mRNA levels were measured 10 or 24 h later. No effect of surfactant treatments, type of surfactant, or dosage (1 or 2 treatments) was noted on SP-A, SP-B, or SP-C mRNA expression. These data indicate that the mRNA expression for the three major surfactant proteins was highest late in gestation in developing rabbits and that exogenous surfactant treatment was not associated with significant changes in SP-A, SP-B, or SP-C mRNA levels.

Animals↗
PubMed1994

Corticosteroids and fetal intervention interact to alter lung maturation in preterm lambs.

The relationship between cortisol infusion and time of fetal catheterization on postnatal lung function of prematurely delivered lambs was investigated with the hypothesis that the intervention of catheterization would alter fetal responsiveness to the maturational effects of corticosteroids. Fetal catheterization was performed on d 117 or on d 122 of gestation. Cortisol or saline control infusions were begun on d 126, with delivery 60 h later on d 128. The animals were ventilated for 1.25 h after delivery, and compliance, the ventilation efficiency index, labeled albumin leak into and out of the lungs, alveolar and lung saturated phosphatidylcholine and surfactant protein A were measured to evaluate lung performance and biochemical indicators of maturation. Cortisol improved compliance and ventilation efficiency and decreased labeled albumin recovery without changing alveolar saturated phosphatidylcholine or surfactant protein A in the animals catheterized at 122 d relative to 122-d saline-infused animals. However, the animals catheterized at 117 d and infused with saline were as mature as assessed by compliance and ventilation efficiency as the 122-d cortisol-treated animals. The 117-d cortisol-infused animals had significantly augmented lung function relative to either 117-d saline-infused or 122-d cortisol-treated lambs and were the only group that had increased alveolar surfactant protein A and lung saturated phosphatidylcholine pool sizes. This study demonstrates that the response of the fetal lung to a maturational agent such as cortisol is dependent on the history of previous fetal interventions.

Albumins↗
PubMed1993

Lung responses to ultrasound-guided fetal treatments with corticosteroids in preterm lambs.

Maternal corticosteroid treatments augment lung function in the human preterm infant. However, not all fetuses respond, the response requires > or = 48 h of exposure, and multiple maternal doses expose the mother to potential risks. To evaluate the potential of direct fetal therapy, we used ultrasound to direct fetal intramuscular or intravascular injections of corticosteroids or saline in sheep and subsequently delivered the preterm lambs at 128 days gestational age to assess postnatal lung function. Relative to saline-injected controls, 0.5 or 2 mg/kg betamethasone given as a single intramuscular dose 48 h before delivery increased compliance and the efficiency of ventilation (as measured by an indicator that included ventilatory pressures and CO2 values) nearly twofold (P < 0.05). Lung volumes, measured from deflation pressure-volume curves, also increased (P < 0.05). However, the 2 mg/kg dose caused severe pulmonary interstitial emphysema in 5 of 13 lambs, suggesting adverse effects. An intravascular fetal dose of 12.5 mg/kg hydrocortisone or an intramuscular dose of 0.1 mg/kg betamethasone had no effect on postnatal lung function. In separate studies, the 2 mg/kg dose improved all indicators of lung function almost twofold after only 24 h of fetal exposure and delivery at 128 days gestational age (P < 0.01). There was a dose-dependent suppression of the postnatal cortisol surge in treated animals, although fetal treatment did not alter cord cortisol levels. Single-dose fetal hormone treatments can cause large and rapid improvements in postnatal lung function in preterm lambs.

Adrenal Cortex Hormones↗
PubMed1993

The development of a radioimmunoassay for reverse triiodothyronine sulfate in human serum and amniotic fluid.

Sulfated iodothyronines including T4-sulfate (T4S) and T3-sulfate (T3S) have been identified in human serum and amniotic fluid. Little is known, however, about the existence of sulfate conjugation of reverse T3 (rT3S) in man. In this report, we employed a novel, sensitive, and specific rT3S RIA to address this question. The rabbit antiserum to rT3S was highly specific; T4, T3, rT3, and 3,3'-T2 showed less than 0.002% cross-reaction with the antiserum. Only T4S and T3S cross-reacted significantly (0.3% and 0.01%, respectively); other analogs cross-reacted less than 0.0001%. The detection threshold of the RIA was 14 pmol/L (1.0 ng/dL). The mean serum rT3S concentration (pmol/L) was 40 in euthyroid subjects. Values were similar in hypothyroid patients (38) and pregnant women (52) but significantly (P < 0.01) elevated to 176 in hyperthyroid patient, 74 in patients with nonthyroid illnesses, and 684 in cord sera of newborns. Serum rT3S increased significantly in hyperthyroid patients 1 day after administration of 1 g sodium ipodate orally. Reverse T3S was detected consistently in amniotic fluid at 14 to 22 weeks of gestation and showed a marked rise 1-3 weeks after intraamniotic administration of 500-1000 micrograms T4. The various data suggest that: (1) rT3S is a normal component of human serum and amniotic fluid; (2) it is derived from metabolism of T4 or rT3; (3) circulating rT3S increases in hyperthyroidism and in circumstances where type I 5'-monodeiodinating activity is low, e.g. nonthyroid illnesses, fetal life, and after administration of ipodate.

Amniotic Fluid↗
PubMed1992

Identification of thyroxine-sulfate (T4S) in human serum and amniotic fluid by a novel T4S radioimmunoassay.

Recently, we identified significant amounts of thyroxine sulfate (T4S) in fetal sheep serum, meconium, bile, and amniotic and allantoic fluids. Little is known, however, about sulfate conjugation of thyroxine in humans. In this study, we employed a novel, sensitive T4S RIA to address this question. The rabbit antiserum was quite specific; T4, T3, rT3, and 3,3'-T2 showed less than 0.002% cross-reactivity. Other analogs cross-reacted less than 0.0001%. Only rT3S and T3S cross-reacted significantly (9.9% and 2.0%, respectively). The mean serum T4S concentration (ng/dL) was 8.6 in euthyroid subjects, 14.4 in hyperthyroid subjects, 5.0 in hypothyroid subjects, 5.9 in pregnancy, and 4.5 in patients with nonthyroid illnesses. T4S concentration in amniotic fluid from women at 18-19 weeks of gestation (25.5 ng/dL) was higher than that at 14-15 weeks of gestation (14.3 ng/dL). A significant rise in serum T4S was detected in hyperthyroid patients 1 day after ingestion of 1 g of ipodate. These data suggest that T4S is a normal component of human serum and amniotic fluid, and it is mostly derived from T4 peripherally and accumulates when type I 5'-monodeiodinating activity is low in fetuses or inhibited by drugs, such as ipodate.

Amniotic Fluid↗
PubMed1992

Thyroxine sulfate is a major thyroid hormone metabolite and a potential intermediate in the monodeiodination pathways in fetal sheep.

T3 and rT3 production rates in the fetus account for roughly only a third of the total T4 production rate; thus, the fate of the majority of T4 produced in the fetus is unknown (the "T4 disposal gap"). We developed sensitive and specific T4 sulfate (T4S) and T3 sulfate (T3S) RIAs to investigate the roles of these compounds in fetal T4 metabolism. T3, T4, T3S, and T4S were determined in a variety of tissue fluid and/or serum samples obtained from fetal, newborn (n = 6), and adult (n = 6) sheep. Four groups of fetal animals, with gestational ages of 94 days (n = 5), 110-111 days (n = 6), 130-131 days (n = 6), and 145 days (n = 6; term = 150 days), were studied. In addition, type I 5'-monodeiodinase (5'-MDI) activity was quantified in liver and kidney tissues. 5'-MDI activities were lower in 94- to 131-day-old fetuses than in fetuses near term or in newborn animals. Mean serum T3 concentrations increased progressively from 94 days (19 ng/dl) to term (371 ng/dl), while mean T3S and T4S serum concentrations were highest at 130 days gestation (237 and 989 ng/dl), decreasing to term. Serum T3S and T4S concentrations decreased further in newborns and adult sheep. T4S and T3S levels in allantoic fluid were significantly higher than those in urine and amniotic fluid in all fetal age groups studied. T4S levels in bile were high from 94-130 days gestation (873-1006 ng/dl), decreasing by 50% at term (529 ng/dl). T4S concentrations in meconium were 46- to 83-fold higher than those in bile from 94 days gestation to term. In contrast, bile T3S levels increased progressively from 94-145 days gestation (191-605 ng/dl), while meconium T3S levels decreased during the same period (33-14 micrograms/100 g). These data demonstrate that 1) sulfated iodothyronines, particularly T4S, are major thyroid hormone metabolites in the fetus; 2) both T4S and T3S are excreted into bile and urine and concentrated in meconium and allantoic fluid; and 3) the high levels of T4S and T3S in serum and other fluids may reflect lower tissue type I 5'-MDI activities. We speculate that T4S and T3S may be further metabolized to other sulfated metabolites and may account in part for the T4 disposal gap in fetal sheep.

Allantois↗
PubMed1991

Corticosteroid and thyrotropin-releasing hormone effects on preterm sheep lung function.

Four groups of twin sheep fetuses were catheterized at 121 days of gestational age and intravenously infused with saline, 0.75 mg.kg-1.h-1 cortisol for 60 h, five intermittent bolus injections of 5 micrograms/kg thyrotropin-releasing hormone (TRH) at 12-h intervals, or both hormones before delivery at 128 days. At birth, the lambs were randomized to receive surfactant or no treatment. Surfactant treatment improved lung function of all the groups. Corticosteroids alone and in combination with TRH improved compliance and gas exchange as well as pressure-volume curves. Corticosteroids alone dramatically decreased the recovery of intravenously administered radiolabeled albumin in the lung tissue and air space and improved the pulmonary response to surfactant treatment. There were no additional effects of TRH when given with corticosteroids on lung function or albumin leak. There were no changes in alveolar surfactant-saturated phosphatidylcholine pool sizes after any hormone treatment. The single significant effect of combined corticosteroid and TRH treatment was a fivefold increase in surfactant protein A in alveolar lavage fluid relative to all other groups.

Animals↗
PubMed1989

Nuclear thyroid hormone receptors: ontogeny and thyroid hormone effects in sheep.

To investigate the mechanism(s) responsible for the paucity of fetal thyroid hormone effects, thyroid hormone nuclear receptor (T3NR) binding characteristics were quantified in liver and brain of fetal and neonatal sheep. Maximal binding capacities [MBC; mean +/- SE fmol 3,5,3'-triiodothyronine (T3)/mg DNA] in liver increased from values of 68 +/- 14 at 80 days gestation to 684 +/- 152 at term. Liver T3NR MBC in newborn and adult sheep were comparable to values in term fetuses. Liver T3NR binding affinities were similar in all animals, averaging 1.68 +/- 0.05 X 10(9) M-1. Brain T3NR MBC were comparable at all fetal ages studied (410 +/- 55 fmol T3/mg DNA), increasing to 1,517 +/- 315 fmol T3/mg DNA during the 1st postnatal week and returning to comparable fetal values (368 +/- 37 fmol T3/mg DNA) in the 3rd week after birth. Brain T3NR binding affinities were comparable in all animals studied (7.5 +/- 2.1 X 10(9) M-1), and the mean value was significantly greater than mean liver T3NR affinity. T3NR binding of T3 analogues in six term fetal animals were qualitatively similar for both brain and liver and showed T3 = triiodothyroacetic acid greater than thyroxine greater than reverse T3. Like T3 binding affinity, T3NR analogue binding affinities in brain tissue were five- to sevenfold greater than those in liver. Fetal hypothyroidism induced by thyroidectomy at either 99-107 or 129-132 days of gestation was not associated with changes in brain or liver T3NR binding characteristics. The heterogenous ontogeny and binding characteristics of brain and liver T3NR is compatible with the hypothesis that different thyroid hormone receptors are expressed in these tissues.

Animals↗
PubMed1976

Influence of hycanthone on morphology and serotonin uptake of Schistosome mansoni.

The intrinsic content of serotonin (5HT) and the uptake of 5HT by Schistosoma mansoni taken from mice which were given a single intramuscular therapeutic dose of hycanthone were studied. Drug-exposed worms were found to have intrinsic values of 5HT which were similar or slightly less than controls. Uptake measurements were made on single and on paired worms recovered from mesenteric, portal, or hepatic sites and incubated in 75% horse serum or in Fischer's medium. All groups of treated worms were found to take up, on average, similar or lower amounts of 5HT compared to controls. These findings are in contrast to a recent report of very considerable increases in content or in 5HT acquisition in vitro by hycanthone-exposed parasites. This communication suggests that the mode of action of hycanthone cannot be explained as being due to increased 5HT uptake. Morphological changes in hycanthone-treated worms include loss of body weight and size, loss of hemoglobin pigment from the gut, deterioration of the tegument, and derangement of the vitellaria. The loss of gut contents occurs early after exposure to hycanthone and may indicate that interference with gut physiology and the nutritional state of the worms is one consequence of the drug, although the mechanism of these changes has not yet been elucidated.

Animals↗