Biomedical subjects

M I Castro

Publications and source records attributed to M I Castro.

At least 19 recordsLinked to original sources

PubMed2001

Airway ammonia negates the normal ventilatory response to airway CO(2) in garter snakes.

Earlier studies from this lab showed that unidirectionally ventilated snakes, maintained on high airway [CO(2)], breathe slowly with a large tidal volume. If airway [CO(2)] is abruptly reduced during inspiration, inspiratory duration (TI) and tidal volume increase. On the other hand, in an animal normally receiving fresh air (no CO(2) in the inspired air) on each inspiration, if fresh air is withheld for one breath, TI and tidal volume decrease. To test the effect of producing an alkaline environment in the presence of CO(2) during these two maneuvers, six unidirectionally ventilated snakes weighing 32+/-16 g were maintained on 4% CO(2) in air flowing at 300 ml/min even during inspiration. NH(3) (4%) was introduced into the lung during one inspiration. During that breath, TI increased significantly, as if CO(2) had been removed from the lung. In another study, six different snakes weighing 21+/-6 g received fresh air at each inspiration. At the end of inspiration [CO(2)] was again raised to 4%. However, for one breath, [CO(2)] was maintained high during inspiration and airway NH(3) (3--4%) was simultaneously introduced into the airstream. During this breath, TI was expected to decrease, owing to the elevated [CO(2)]; however, there was no significant difference in the TI of the test breath compared with the previous breath, indicating that ammonia interfered with the expected CO(2) response. This study suggests that pH (probably intracellular) rather than P(CO(2)) produces this ventilatory reflex.

Administration, Inhalation↗

PubMed1999

Ontogeny of estrogen sulfatase activity in ovine fetal hypothalamus, hippocampus, and brain stem.

Ovine parturition is initiated by increases in fetal hypothalamus-pituitary-adrenal (HPA) axis activity, which in turn increase placental estrogen biosynthesis and ultimately increase uterine contractility. In addition to the action in the uterus, estrogens augment fetal ACTH secretion. In late gestation, estrone sulfate is more abundant in fetal plasma than is unconjugated estrone. We studied hypothalamus, hippocampus, and brain stem tissue from fetal, neonatal, and adult sheep to test the hypothesis that the ovine brain contains estrogen sulfatase activity. We found that the activity in the hippocampus was significantly increased in late-gestation fetuses compared with both younger and older animals. No significant change in either hypothalamus or brain stem was revealed; however, the activity in all brain areas was high. Immunohistochemistry revealed the presence of estrogen sulfatase in the paraventricular nucleus of the hypothalamus, the nucleus of the solitary tract, and the rostral ventrolateral medulla. We conclude that ovine fetal hypothalamus, hippocampus, and brain stem contain estrogen sulfatase activity and that the activity in the hippocampus is developmentally regulated.

Aging↗

PubMed1998

Fetal pulmonary immunoreactive adrenocorticotropin: molecular weight and cellular localization.

The hypothalamus-pituitary-adrenal axis of the sheep fetus plays a critical role in fetal development, responsiveness to stress, and initiation of parturition. We have recently reported that the fetal lung contains and secretes significant amounts of immunoreactive adrenocorticotropin (iACTH). The present study was designed to identify the molecular weight profile and the cellular location of iACTH in this tissue. iACTH extracted from fetal lung was immunoprecipitated, electrophoresed, and immunoblotted. Pulmonary iACTH was found in several molecular forms. The largest peptides appeared as doublets, and had molecular weights similar to POMC (32, 33 kD). Smaller peptides appeared in molecular weights (17, 24, and 27 kD) which were not consistent with the post-translational processing of POMC in fetal pituitary, but which were consistent with known processing of POMC by chromaffin granule aspartyl protease. None of the molecular forms of iACTH were glycosylated. Immunohistochemistry revealed that the iACTH was contained within bronchial epithelium and within groups of cells within the parenchyma of the lung. Both of these types of cells are consistent with pulmonary neuroendocrine cells. The distribution of neuroendocrine cells and apparent concordance with the iACTH-positive cells was confirmed by immunostaining for neuron specific enolase, a marker for neuroendocrine cells within the lung. We conclude that the lung contains unprocessed and partially processed POMC within cells known to contain neuropeptides. We speculate that secretion of the POMC-related peptides from these cells is physiologically important in the late-gestation fetus.

Adrenocorticotropic Hormone↗

PubMed1996

ACTH-like bioactivity and immunoactivity in fetal lamb pituitaries at 0.65 and 0.95 gestation.

We wished to determine if the concentration of bioactive ACTH-like activity increased during development and if there was heterogeneity in ovine fetal anterior pituitary ACTH activity as measured by bioassay and radioimmunoassay (RIA). We obtained anterior pituitaries from eight sheep fetuses (four at 0.65 and four at 0.95 gestation; term 145 +/- 5 days) and extracted and homogenized them in ice-cold 5N acetic acid, 0.3% phenylmethanesulfonyl fluoride (PMSF) and 0.2% BSA. Fractionation of each pituitary extract was performed by size-exclusion chromatography using Sepadex G-50. The ACTH-like immunoactivity (ALI) profile for each pituitary showed two well-defined peaks. One eluted with human ACTH1-39 and the other eluted with the high molecular weight fraction in the void volume. Four fractions from the first peak representing the high molecular weight forms of ACTH activity and four fractions from the second peak representing the low molecular weight forms of ACTH activity were pooled separately. These two pools were subjected to reverse-phase chromatography (RPC) on a C-8 column using a linear gradient of 70% acetonitrile in 0.8% trifluoroacetic acid over a 60 min period. Based upon the RIA, the high molecular weight forms of ACTH from the G-50 column were resolved into three main fractions, one eluting similar to the standard ACTH1-39 and the remaining two eluting after that. The low molecular weight forms of ACTH from the G-50 column were resolved into three peaks, before, with, and after the standard. We used collagenase-dispersed rat adrenal cells to test the ACTH-like bioactivity (ALB) of the crude extracts and of the different fractions obtained from the RPC of the high and low molecular weight material. The concentration of ACTH-like bioactivity in the crude extracts was similar at the two stages of gestation. However, there was a trend for the low molecular weight peak to have more peptide eluting with human ACTH1-39 and higher ratios of ALB/ALI than did the high molecular weight peak. These results suggest that multiple ACTH molecular forms with different ALB/ALI ratios are present in the ovine fetal pituitary and that there is no selective increase in ACTH1-39 concentration in the fetal pituitary in late gestation.

Adrenocorticotropic Hormone↗

PubMed1993

Bioactive-to-immunoreactive ACTH activity changes with severity of stress in late-gestation ovine fetus.

The late-gestation ovine fetus (> 130 days, 0.90 gestation, full term 145 days) is capable of increased pituitary-adrenal activity following a variety of stressors. To examine the relationship between plasma immunoreactive adrenocorticotropic hormone (iACTH) and bioactive ACTH-like activity (bACTH), late-gestation fetuses were studied under nonstress (group I, chronically catheterized), "mild" stress (group II, acutely exteriorized), or marked stress (group III, acutely exteriorized and hemorrhaged 30% of blood volume). Plasma iACTH was determined by standard radioimmunoassay. Plasma bACTH was determined by a bioassay that utilized dispersed rat adrenal cells. Plasma iACTH was lower in group I than in groups II or III (78.4 +/- 16.3 vs. 320 +/- 116 and 622 +/- 144 pg/ml, respectively, mean +/- SE, P < 0.05 group I vs. III). Plasma bACTH was significantly lower in groups I and II than in group III (13.8 +/- 2.7 and 52 +/- 22 vs. 601 +/- 106 pg/ml, respectively, P < 0.05). The ratio of bACTH to iACTH was low in groups I and II but elevated in group III (0.188 +/- 0.028 and 0.091 +/- 0.07 vs. 0.996 +/- 0.122, P < 0.05). We conclude that the amount of bACTH compared with iACTH in the late-gestation fetus is low under nonstress states or mild stress and that bACTH increases disproportionately compared with iACTH after marked stress. This suggests that a change in ACTH processing and/or secretion is associated with stimulus intensity in the late-gestation ovine fetus.

Adrenocorticotropic Hormone↗

PubMed1993

Content, in vivo release, and bioactivity of fetal pulmonary immunoreactive adrenocorticotropin.

We hypothesized that fetal lung contains and releases immunoreactive (ir) adrenocorticotropin (ACTH). Fetal sheep lung (89-145 days gestation, n = 13) irACTH content was 4,100 +/- 672 (SE) pg/g lung wet wt compared with 5,425 +/- 1,403 (SE) pg/g in adults (n = 5) when measured by radioimmunoassay (RIA). irACTH values normalized to protein content were 158 +/- 18 and 95 +/- 22 (SE) ng/g protein for fetuses and adults, respectively. Grouped by age, < 90 days (n = 4), 131-139 days (n = 5), and 143-145 days (n = 4), the values for irACTH were 184 +/- 28, 173 +/- 33, and 114 +/- 33 (SE) ng/g protein, respectively, and declined significantly from < 90 days to adulthood. RIA serial dilution curve slopes were different from standard in 7 of 13 fetuses and in all adults, suggesting that irACTH structure differs from ACTH-(1-39). Acute in vivo fetal pulmonary artery and vein sampling (n = 5, 120-128 days gestation) revealed a mean difference of -609 +/- 476 (SE) pg/ml, a statistically significant release of irACTH across the lung. Western blotting revealed that pulmonary irACTH migrates in multiple immunostaining bands between molecular weight 14,000 and 46,000 and does not colocalize with ACTH-(1-39). Adrenal cell bioassay revealed that pulmonary irACTH is not corticotropic. We concluded that ovine fetal lung contains large-molecular-weight irACTH, that content declines from 90 days gestation to adulthood, and that, under acute conditions, the fetal lung releases irACTH substances in sufficient quantity to contribute to circulating hormone concentrations of irACTH.

Adrenocorticotropic Hormone↗

PubMed1992

Corticotropin and cortisol responses to corticotropin-releasing factor in the chronically hypoxemic ovine fetus.

OBJECTIVE: The purpose of this study was to determine if mild hypoxemia (approximately 25% below normal) of at least 5 days' duration alters corticotropin and cortisol responses to corticotropin-releasing factor. STUDY DESIGN: We studied 14 (hypoxemic, n = 5; normoxemic, n = 9) fetuses of 135 +/- 1 (mean +/- SEM) days' gestational age. Fetuses were placed in the experimental group if arterial PO2 was < or = 16 mm Hg for 5 days. In normoxemic animals arterial PO2 was > or = 17 mm Hg. Plasma hormone responses were compared by analysis of variance. RESULTS: Resting corticotropin levels were not different (hypoxemic 26 +/- 5 pg/ml, normoxemic 29 +/- 12 pg/ml), and corticotropin-releasing factor (530 +/- 30 ng/kg) increased (p = 0.01) corticotropin levels similarly in both groups. Basal plasma cortisol levels (hypoxemic 20 +/- 10 ng/ml, normoxemic, 30 +/- 7 ng/ml) were not significantly different. Both groups had similarly increased (p < 0.01) plasma cortisol levels after corticotropin-releasing factor administration. CONCLUSION: Mild hypoxemia lasting 5 days does not significantly alter corticotropin and cortisol responses to corticotropin-releasing factor in the late-gestation ovine fetus.

Adrenocorticotropic Hormone↗

PubMed1992

ACTH and cortisol responses to sequential CRF injections in fetal sheep.

To determine whether an initial ovine corticotropin-releasing factor (oCRF) injection modifies adrenocorticotropic hormone (ACTH) and cortisol responses to a second injection and to establish whether the effect changes throughout gestation, we studied chronically cannulated fetal lambs of 103-113 and 133-137 days gestation. Experimental groups underwent an injection (500 ng/kg iv) of oCRF, arterial blood sampling for 6 h, then a similar oCRF injection followed by sampling. In control studies, vehicle was the initial injection. After the first oCRF injection, plasma cortisol levels went from 1.7 +/- 0.4 to 9.5 +/- 5.2 (SE) ng/ml ("immature") and from 22.3 +/- 4.9 to 52.5 +/- 5.8 ng/ml ("mature"), remaining elevated for 6 h. In immature fetuses, the first oCRF injection did not alter the ACTH response to a second injection. Cortisol increases were reduced. In mature animals, ACTH and cortisol response to oCRF were eliminated by prior oCRF. Thus a large increase in cortisol after oCRF in mature fetuses is associated with inhibition of the ACTH response to a second oCRF injection, whereas in immature animals a small increase in cortisol after the first oCRF injection is not.

Adrenal Cortex↗

PubMed1992

ACTH and cortisol responses to hypotension in fetal sheep after a prior CRF injection.

To determine whether an ovine corticotropin-releasing factor (oCRF) injection modifies adrenocorticotropic hormone (ACTH) and cortisol responses to hypotension and whether the effect of any interactions between these stimuli changes across gestation, we studied chronically cannulated fetal lambs of 103-113 ("immature") and 133-139 days gestation ("mature"). Experimental groups received 500 ng/kg oCRF injections and 6 h later had arterial pressure reduced 20% for 10 min with nitroprusside. Blood samples were obtained before and after each manipulation. Controls received vehicle instead of oCRF. The oCRF increased plasma cortisol levels from 2.1 +/- 0.4 to 14.2 +/- 4.7 (SE) ng/ml in immature and 44.9 +/- 2.2 to 102.8 +/- 15 ng/ml in mature animals. In mature fetuses the oCRF did not alter plasma ACTH and cortisol increases due to hypotension. In immature animals ACTH increases were normal but cortisol increases were eliminated. This suggests that the CRF caused maximal stimulation of the adrenal gland. In older fetuses, it appears that the action of ACTH-releasing factors, secreted in response to arterial hypotension, can overcome the negative feedback effects of elevations in endogenous cortisol.

Adrenal Cortex↗

PubMed1992

The ratio of plasma bioactive to immunoreactive ACTH-like activity increases with gestational age in the fetal lamb.

The fetal ovine pituitary-adrenal axis plays an important role in the timing of parturition, in fetal lung maturation, and in fetal and neonatal responses to stress. While the ovine pituitary during the last third of gestation (term = 145 days) is capable of secreting immunoreactive ACTH (iACTH) in response to various stimuli, plasma cortisol levels frequently do not reflect the rise in plasma ACTH. Therefore, we examined the relationship between plasma iACTH and steroidogenic ACTH-like activity (bACTH) in a group of immature fetal lambs (Group I: gestational age = 97 +/- 2 days, mean +/- SEM, n = 16) and a group of near-term fetuses (Group II: gestational age = 136 +/- 1 days, n = 13) following acute exteriorization. Plasma iACTH was determined by RIA. Plasma bACTH was determined by the ability of glass-extracted material to stimulate corticosterone (B) production in an acutely dispersed rat adrenal bioassay. Plasma iACTH and bACTH levels varied among animals within age groups, with iACTH tending to be higher in immature fetal lambs (Group I) than near-term lambs (Group II) and bACTH being higher (P < 0.05) near term than earlier (Group I: iACTH = 807 +/- 273 pg/ml, bACTH = 173 +/- 44 pg/ml; Group II: iACTH = 405 +/- 85 pg/ml, bACTH = 371 +/- 96 pg/ml). The proportion of iACTH that had biologic activity (e.g. B/I ratio) was significantly greater in the older than in the younger fetuses (Group II: B/I = 0.862 +/- 0.109; Group I: B/I = 0.462 +/- 0.105 P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenocorticotropic Hormone↗

PubMed1989

Intravenous clonidine hydrochloride toxicity in pregnant ewes.

Administration of intravenous clonidine hydrochloride has been advocated to rapidly control blood pressure in severe preeclampsia. To examine clonidine's acute maternal and fetal effects were intravenously injected 300 micrograms clonidine in eight chronically prepared normotensive near term ewes. Unlike intravenous saline solution injection, clonidine produced significant toxicity--intraamniotic pressure increased 97 +/- 27% (p less than 0.05), uterine blood flow decreased 55 +/- 7% (p less than 0.001), maternal and fetal serum glucose increased 158 +/- 23% and 249 +/- 91%, respectively (p less than 0.001), and maternal and fetal Po2 decreased to 44 mm Hg +/- 4 mm Hg and 13 mm Hg +/- 1 mm Hg, respectively (p less than 0.05). Maternal and fetal blood pressure and serum cortisol were unaffected by clonidine, whereas heart rate decreased. No adverse maternal or fetal effects were noted with serum clonidine concentrations less than 1.0 ng/ml. Direct fetal infusion of clonidine did not lower fetal arterial Po2 levels, although heart rates decreased and serum glucose levels increased. The multiple effects of clonidine infusion are best explained by actions on alpha 2-adrenergic receptors. These results suggest that intravenous administration of clonidine may adversely affect the fetus by direct actions and by alterations in maternal physiology.

Animals↗

PubMed1989

Epidural clonidine analgesia in obstetrics: sheep studies.

Epidural clonidine administration produces analgesia by a nonopiate, spinal mechanism, and offers advantages over other epidural agents for labor analgesia. To examine clonidine's acute maternal and fetal effects, the authors injected clonidine, 300 micrograms, epidurally in seven chronically prepared, near term ewes. Unlike epidural saline injection, clonidine increased maternal and fetal serum glucose (by 178 +/- 30% and 190 +/- 30%, respectively; mean +/- SEM, P less than .01) 1 h following injection. Maternal and fetal serum cortisol and arterial blood gas tensions were unchanged following clonidine. Epidural clonidine injection produced minor decreases (10-15%) in heart rate in ewe and fetus, without altering maternal and fetal blood pressure, intra-uterine pressure, or uterine blood flow. Maternal and fetal serum clonidine concentrations peaked at 58 +/- 8 and 73 +/- 5 min following injection, respectively, and declined with similar half-lives. Heart rate correlated negatively with serum clonidine concentration in both ewe and fetus (P less than .05). Apart from hyperglycemia, which does not occur in humans, these results in sheep suggest that epidurally administered clonidine does not adversely affect the fetus and may be evaluated as an analgesic in obstetrics.

Analgesia, Epidural↗

PubMed1989

Pharmacokinetics and dynamics of intravenous, intrathecal, and epidural clonidine in sheep.

Epidural clonidine administration produces analgesia by a spinal action but may produce hemodynamic depression by activating other central or peripheral alpha 2-adrenoceptors. To determine clonidine's distribution and cardiorespiratory effects 300 micrograms clonidine was injected epidurally, intrathecally, and intravenously in six chronically prepared sheep, and cerebrospinal fluid (CSF) and arterial plasma clonidine were measured. Dural transfer of epidurally administered clonidine was rapid and extensive: time to maximal concentration (Tmax) in CSF was 32 +/- 8 min, bioavailability in CSF was 14 +/- 4% of the administered dose, and maximal CSF concentrations following epidural administration (820 +/- 30 ng/ml) were three orders of magnitude greater than those following iv injection (0.71 +/- 0.06 ng/ml). Systemic absorption of epidurally administered clonidine occurred rapidly: Tmax in plasma was 34 +/- 6 min and plasma concentrations were similar to those following iv injection at all time points beyond 20 min. Elimination half-lives from plasma were similar for all three routes of administration (81-95 min). Clonidine's effect on blood pressure differed with route of administration. Blood pressure increased and heart rate decreased following iv injection when plasma clonidine concentrations were high (greater than 2 ng/ml). Clonidine, following all routes of administration, numerically decreased blood pressure, but this decrease was significant only following epidural (mean arterial pressure = 97 +/- 6 mmHg before, 86 +/- 6 mmHg after; P less than 0.05) and intrathecal (93 +/- 9 mmHg before, 79 +/- 10 mmHg after; P less than 0.05) injection. Blood pressure decreased earlier following intrathecal than following epidural injection, corresponding with higher CSF clonidine concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Maternally administered esmolol produces fetal beta-adrenergic blockade and hypoxemia in sheep.

Although esmolol may be a useful therapeutic agent in obstetrics and obstetric anesthesia, concerns about fetal safety have limited its use. To assess acute fetal hemodynamic effects of maternally administered esmolol, saline or esmolol (4-200 micrograms.kg-1.min-1 in a stepped manner) was infused into maternal venous catheters in nine chronically prepared pregnant ewes, and the degree of beta-adrenergic blockade was assessed by isoproterenol challenge. In control experiments saline infusion and repeated isoproterenol challenges did not alter measured parameters, although maternally administered isoproterenol (0.1 micrograms) transiently decreased uterine blood flow by 20 +/- 5% (mean +/- SEM; P less than 0.05). Esmolol produced a dose-dependent decrease in maternal blood pressure and fetal heart rate (maternal blood pressure decreased by 22 +/- 8% and fetal heart rate decreased by 27 +/- 7% following esmolol, 200 micrograms.kg-1.min-1; P less than 0.05). Fetal arterial PO2 decreased from 18.2 +/- 1.2 mmHg before to 14.1 +/- 1.5 mmHg following esmolol, 200 micrograms.kg-1.min-1 (P less than 0.05). Maternally administered esmolol produced similar dose-dependent beta-adrenergic blockade in both ewe and fetus, with complete blockade following the 80 and 200 micrograms.kg-1.min-1 doses. Thirty minutes following cessation of esmolol infusion, fetal resting heart rate and maternal and fetal isoproterenol-stimulated heart rate remained below control values. These results suggest that maternally administered esmolol may produce adverse fetal effects, limiting its usefulness in the obstetric setting.

Acids↗

PubMed1988

The effect of thyroid dysfunction and fasting on placenta inner ring deiodinase activity in the rat.

The placenta contains iodothyronine 5-deiodinase activity (P5-Dase) that probably acts on iodothyronines in the fetal circulation to convert T4 to rT3 and T3 to 3,3'-T2. Since thyroid status and fasting have profound effects on iodothyronine deiodinases in other tissues, the present studies were performed to determine if these perturbations affected P5-Dase. Control and treated rats were mated and killed near term on the 20th day of gestation. P5-Dase was determined in placenta homogenates enriched with dithiothreitol by measuring the conversion of T4 to rT3. In four of five studies, P5-Dase was similar in dams that underwent thyroidectomy (Tx) on day 7 of gestation and sham Tx dams. P5-Dase was not altered in dams that were treated with methimazole (MMI) to induce maternal and fetal hypothyroidism. Treatment of dams with supraphysiological doses of T4, beginning on the seventh day of gestation, did not significantly affect P5-Dase. In three of four studies, P5-Dase was similar in fed dams to values in dams fasted for the last 5 days of pregnancy. Placenta iodothyronine 5'-deiodinase activity (P5'-Dase) was also measured in some studies. P5'-Dase was not decreased in Tx rats and was modestly decreased in MMI-treated rats. However, the effect of MMI was not reversed by the administration of supraphysiological doses of T4, Tx, MMI treatment, and fasting all decreased hepatic T4 5'-deiodinase activity in pregnant rats. These results strongly suggest that thyroid status and fasting do not alter P5-Dase activity.

Animals↗

PubMed1986

Total and free serum thyroid hormone concentrations in fetal and adult pregnant and nonpregnant guinea pigs.

Information on total and free serum thyroid hormone concentrations in the adult and fetal guinea pig (Cavia porcellus) is limited. These variables were studied in adult male and female guinea pigs and in pregnant guinea pigs and their fetuses at various times during gestation. Total serum T4 levels in adult males, nonpregnant females, and pregnant females did not differ significantly [range, 2.5 +/- 0.3 to 3.2 +/- 0.8 micrograms/dl (mean +/- SD)]. Similarly, there were no significant differences in the percent free T4 (0.046-0.068%), free T4 (1.26-2.03 ng/dl), total T3 (39-44 ng/dl), the percent free T3 (0.521-0.638%), and free T3 (0.221-0.260 ng/dl) among adult males, nonpregnant females, and pregnant females. rT3 was undetectable in adult male, nonpregnant female, and pregnant female guinea pig serum. T4 values were similar and those for T3 were lower in fetal compared to maternal serum at 45 days of gestation, whereas serum rT3 was detectable in fetal serum. Between 45 and 62 days of gestation, fetal serum T4 increased from 2.5 to 0.3 to 4.3 +/- 1.3 micrograms/dl (mean +/- SD, P less than 0.01), fetal serum T3 remained unchanged, and fetal serum rT3 increased from 5.2 +/- 3.3 to 25.0 +/- 11.4 ng/dl (P less than 0.01). Near term, fetal serum total and free T4 and total rT3 concentrations were significantly higher and total and free T3 concentrations were significantly lower than the corresponding values in maternal serum. Total serum T4 is higher in the guinea pig than in the rabbit, is similar to values in the rat, and is lower than values in man. The free T4 concentration in guinea pig serum is similar to those in humans and rats. The ontogenesis of thyroid hormones differs strikingly in the guinea pig fetus compared to that in the rat fetus and shares many similarities with sheep and human fetal thyroid development.

Animals↗

PubMed1986

Fetal plasma insulin and thyroid hormone levels during acute in utero ethanol exposure in a maternal-fetal sheep model.

The effects of acute in utero ethanol (ETOH) treatment on basal and stimulated thyroid and insulin levels in fetal plasma were studied in chronically cannulated fetal sheep. In test situations, pregnant ewes (0.78-0.88 gestation) which were chronically cannulated received 2 g/kg ETOH [25% (vol/vol) in isotonic saline] for 2 h; this was followed by a maintenance iv infusion of 0.13 g/kg ETOH. Control animals received isovolemic infusions of isotonic saline. Fetal arterial plasma samples were obtained after the 2-h infusion, and basal levels of T3, T4, glucose, and insulin were measured. The 2-h ETOH infusion did not influence fetal basal plasma T3, T4, insulin, or glucose. Fetal thyroid responses to an intraarterial injection of 0.01, 0.10, 1.00, or 10.00 micrograms/kg TRH or of 5 mU/kg TSH through the fetal catheters were studied in the presence or absence of high plasma ETOH concentrations. Fetal T4 or T3 levels during the 4 h following any of these stimuli were not significantly different in ethanol-treated and control animals. The effects of acute ETOH exposure on insulin responses to a glucose challenge were studied in six chronically cannulated ewes and their fetuses using a cross-over experimental design. After the 2-h ETOH infusion, ewes received a bolus injection of 600 mg/kg 50% glucose, followed by a 1-h infusion of 624 mg/kg 50% glucose and 0.13 g/kg ETOH. In control situations, ewes received saline plus glucose. Acute ETOH treatment did not influence maternal or fetal plasma glucose levels at any time, but enhanced both maternal and fetal insulin responses to glucose. Total insulin release, as measured by the area under the insulin response curve, was greater during ETOH exposure in both mother (ETOH, 4740 +/- 1475 microU/ml X min; control, 2807 +/- 766 microU/ml X min; P = 0.05) and fetus (ETOH, 562 +/- 94 microU/ml X min; control, 363 +/- 46 microU/ml X min; P less than 0.05). Thus acute in utero ETOH exposure does not diminish plasma levels of either thyroid hormones or insulin, two important hormones for fetal growth and development. However, ethanol exposure enhances the insulin response to increases in blood glucose in both mother and fetus.

Animals↗

PubMed1985

Inner-ring deiodination of 3,5,3'-triiodothyronine in the in situ perfused guinea pig placenta.

Broken cell preparations of rat and human placentas contain an inner (tyrosyl)-ring iodothyronine deiodinase enzyme with greatest activity when the substrate is 3,5,3'-triiodothyronine (T3). This report describes the deiodination of T3 in the intact placenta and the effect of sodium iopanoate (IA) and propylthiouracil (PTU) on T3 deiodination. Under nembutal anesthesia, the placenta of 60-65-d-old pregnant guinea pigs was surgically exposed, a single umbilical artery and the umbilical vein were cannulated, and the fetus was removed. In a temperature-controlled chamber (37 degrees C), the fetal side of the placenta was perfused through the umbilical artery at a rate of 1 ml/min with 3% bovine serum albumin Krebs-Henseleit buffer containing 0.14 nM outer ring labeled [125I]T3. Placenta effluent fractions were collected at timed intervals from the umbilical vein cannula throughout a 120-min perfusion period. The contents of the perfusion buffer and the various effluent fractions were analyzed for their iodothyronine content by high pressure liquid chromatography. In five experiments, the percent composition of 125I-labeled iodothyronines in the perfusion buffer and placenta effluent was 95.3 +/- 1.0 (mean +/- SE) and 70.2 +/- 2.1 for T3 (P less than 0.01), 2.5 +/- 0.7 and 20.1 +/- 1.8 for 3,3'-T2 (P less than 0.01), and 0 and 8.2 +/- 0.9 for 3'-T1. There was no difference between the percent [125I]iodide in the perfusion buffer and in the placenta effluents. When placentas were perfused with IA and [125I]T3, after perfusion with [125I]T3 alone, there was a significant increase (P less than 0.01) in the percent [125I]T3 in the placenta effluents, and a significant decrease in [125I]3,3'-T2 (P less than 0.01) and [125I]3'-T1 (P less than 0.01). In contrast, PTU did not affect the composition of labeled iodothyronines in the placenta effluents, despite the fact that the addition of PTU significantly (P less than 0.001) inhibits the inner-ring deiodination of [125I]T3 in human or guinea pig placenta microsomes in the presence of low (0.25 mM) concentrations of dithiothreitol. The present studies demonstrate that T3 is actively deiodinated in the inner ring to 3,3'-T2 by the intact guinea pig placenta. A portion of 3,3'-T2 is further deiodinated in the inner ring to generate 3'-T1. No outer ring deiodination of T3 was seen under the conditions employed. IA, but not PTU, inhibits T3 deiodination in the placenta perfused in situ. We conclude that the placenta is probably a site for fetal T3 metabolism.

Animals↗