Long-term hypoxia modulates expression of key genes regulating adrenomedullary function in the late gestation ovine fetus

2007 ◽  
Vol 293 (5) ◽  
pp. R1997-R2005 ◽  
Author(s):  
Charles A. Ducsay ◽  
Kim Hyatt ◽  
Malgorzata Mlynarczyk ◽  
Brandon K. Root ◽  
Kanchan M. Kaushal ◽  
...  
Keyword(s):  
Nicotinic Receptor ◽  
Messenger Rna ◽  
Acute Stress ◽  
Selective Reduction ◽  
Late Gestation ◽  
Fetal Sheep ◽  
Subunit Expression ◽  
Ovine Fetus ◽  
And Control

We previously communicated that long-term hypoxia (LTH) resulted in a selective reduction in plasma epinephrine following acute stress in fetal sheep. The present study tested the hypothesis that LTH selectively reduces adrenomedullary expression of phenylethanolamine-N-methyltransferase (PNMT), the rate-limiting enzyme for epinephrine synthesis. We also examined the effect of LTH on adrenomedullary nicotinic, muscarinic, and glucocorticoid receptor (GR) expression. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dGA); adrenomedullary tissue was collected from LTH and age-matched, normoxic control fetuses at 139–141 dGA. Contrary to our hypothesis, in addition to PNMT, adrenomedullary expression (mRNA, protein) of tyrosine hydroxylase (TH) and dopamine beta-hydroxylase (DBH) were reduced in the LTH fetus. Immunocytochemistry indicated that TH and DBH expression was lower throughout the medulla, while PNMT appeared to reflect a reduction in PNMT-expressing cells. Nicotinic receptor alpha 1, 2, 3, 5, 6, 7, beta 1, 2, and 4 subunits were expressed in the medulla of LTH and control fetuses. Messenger RNA for alpha 1 and 7 and beta 1 and 2 subunits was lower in LTH fetuses. Muscarinic receptors M1, M2, and M3 as well as the GR were also expressed, and no differences were noted between groups. In summary, LTH in fetal sheep has a profound effect on expression of key enzymes mediating adrenomedullary catecholamine synthesis. Further, LTH impacts nicotinic receptor subunit expression potentially altering cholinergic neurotransmission within the medulla. These findings have important implications regarding fetal cardiovascular and metabolic responses to stress in the LTH fetus.

Antenatal glucocorticoids reset the level of baseline and hypoxemia-induced pituitary-adrenal activity in the sheep fetus during late gestation

2004 ◽  
Vol 286 (2) ◽  
pp. E311-E319 ◽  
Author(s):  
Andrew J. W. Fletcher ◽  
Xiao Hong Ma ◽  
Wen X. Wu ◽  
Peter W. Nathanielsz ◽  
Hugh H. G. McGarrigle ◽  
...  
Keyword(s):  
Hpa Axis ◽  
Plasma Cortisol ◽  
Acute Stress ◽  
Cortisol Concentration ◽  
Late Gestation ◽  
Dexamethasone Treatment ◽  
Fetal Sheep ◽  
Plasma Cortisol Concentration ◽  
Basal Plasma ◽  
Ovine Fetus

This study examined the effects of dexamethasone treatment on basal hypothalamo-pituitary-adrenal (HPA) axis function and HPA responses to subsequent acute hypoxemia in the ovine fetus during late gestation. Between 117 and 120 days (term: ∼145 days), 12 fetal sheep and their mothers were catheterized under halothane anesthesia. From 124 days, 6 fetuses were continuously infused intravenously with dexamethasone (1.80 ± 0.15 μg·kg–1·h–1 in 0.9% saline at 0.5 ml/h) for 48 h, while the remaining 6 fetuses received saline at the same rate. Two days after infusion, when dexamethasone had cleared from the fetal circulation, acute hypoxemia was induced in both groups for 1 h by reducing the maternal fraction of inspired O2. Fetal dexamethasone treatment transiently lowered fetal basal plasma cortisol, but not ACTH, concentrations. However, 2 days after treatment, fetal basal plasma cortisol concentration was elevated without changes in basal ACTH concentration. Despite elevated basal plasma cortisol concentration, the ACTH response to acute hypoxemia was enhanced, and the increment in plasma cortisol levels was maintained, in dexamethasone-treated fetuses. Correlation of fetal plasma ACTH and cortisol concentrations indicated enhanced cortisol output without a change in adrenocortical sensitivity. The enhancements in basal cortisol concentration and the HPA axis responses to acute hypoxemia after dexamethasone treatment were associated with reductions in pituitary and adrenal glucocorticoid receptor mRNA contents, which persisted at 3–4 days after the end of treatment. These data show that prenatal glucocorticoids alter the basal set point of the HPA axis and enhance HPA axis responses to acute stress in the ovine fetus during late gestation.

Pituitary and gonadal responses to the long-term pulsatile administration of gonadotrophin-releasing hormone in fetal fetal sheep

1997 ◽  
Vol 153 (3) ◽  
pp. 385-391 ◽  
Author(s):  
G B Thomas ◽  
A N Brooks
Keyword(s):  
Plasma Concentrations ◽  
Reproductive Function ◽  
Inverse Correlation ◽  
Experimental Period ◽  
Immediate Release ◽  
Late Gestation ◽  
Plasma Testosterone ◽  
Fetal Sheep ◽  
Pulsatile Administration

Abstract The fetal hypothalamo–pituitary–gonadal axis reaches a peak in activity at mid-gestation and this is followed by a period of suppression which persists until the onset of puberty. The decline in gonadotrophic activity during late gestation is thought to reflect the maturation of central and peripheral feedback signals. In order to establish if sustained pituitary responsiveness is rate limiting to the reinstatement of reproductive function, we have examined the endocrine consequences of repeated pulsatile GnRH administration to male and fetal sheep during late gestation. Beginning on day 121 of gestation (term=145 days) chronically catheterized fetal sheep were given i.v. pulses of either 500 ng GnRH or saline every 2 h for 14 days. Pituitary and gonadal responses were assessed by measuring changes in plasma concentrations of LH, FSH, inhibin and testosterone (in male fetuses) in response to the first pulse of GnRH on day 1 and to the corresponding pulse on days 4, 7, 10 and 14. In response to the first pulse of GnRH there was an immediate release of LH, with the peak response being significantly (P<0·01) greater than on subsequent days. In male fetuses each pulse of LH was followed by a rise in plasma testosterone concentrations within 40–60 min. The amplitude of these testosterone responses increased significantly (P<0·01) after 9 days of treatment despite a decline in the plasma LH response. Basal FSH concentrations increased progressively (P<0·05) during pituitary stimulation with GnRH in both male and female fetuses. Immunoreactive inhibin concentrations were significantly (P<0·05) higher in males than in females, and there was a gradual increase throughout the experimental period irrespective of treatment. We observed no inverse correlation between inhibin and FSH concentrations. These data show that pulsatile administration of GnRH to fetal sheep during late gestation results in sustained re-activation of pituitary–gonadal function. The decline in fetal gonadotrophins, which is a characteristic feature of late gestation, is therefore likely to result from inadequate GnRH secretion from the fetal hypothalamus rather than an inhibition of pituitary function by peripheral feedback signals. Journal of Endocrinology (1997) 153, 385–391

Urocortin: a mechanism for the sustained activation of the HPA axis in the late-gestation ovine fetus?

2002 ◽  
Vol 283 (1) ◽  
pp. E165-E171 ◽  
Author(s):  
Alison C. Holloway ◽  
David C. Howe ◽  
Gabriel Chan ◽  
Vicki L. Clifton ◽  
Roger Smith ◽  
...  
Keyword(s):  
In Situ Hybridization ◽  
Late Gestation ◽  
Pituitary Cells ◽  
Fetal Sheep ◽  
Antisense Probe ◽  
Pomc Mrna ◽  
Ovine Fetus ◽  
Ovine Fetal ◽  
Sustained Activation

We hypothesized that urocortin might be produced in the pituitary of the late-gestation ovine fetus in a manner that could contribute to the regulation of ACTH output. We used in situ hybridization and immunohistochemistry to identify urocortin mRNA and protein in late-gestation fetal pituitary tissue. Levels of urocortin mRNA rose during late gestation and were associated temporally with rising concentrations of pituitary proopiomelanocortin (POMC) mRNA. Urocortin was localized both to cells expressing ACTH and to non-ACTH cells by use of dual immunofluorescence histochemistry. Transfection of pituitary cultures with urocortin antisense probe reduced ACTH output, whereas added urocortin stimulated ACTH output from cultured pituitary cells. Cortisol infusion for 96 h in chronically catheterized late-gestation fetal sheep significantly stimulated levels of pituitary urocortin mRNA. We conclude that urocortin is expressed in the ovine fetal pituitary and localizes with, and can stimulate output of, ACTH. Regulation of urocortin by cortisol suggests a mechanism to override negative feedback and sustain feedforward of fetal hypothalamic-pituitary-adrenal function, leading to birth.

Suppression of arousal by progesterone in fetal sheep

1997 ◽  
Vol 9 (8) ◽  
pp. 767 ◽  
Author(s):  
Kelly J. Crossley ◽  
Marcus B. Nicol ◽  
Jonathan J. Hirst ◽  
David W. Walker ◽  
Geoffrey D. Thorburn†
Keyword(s):  
Fetal Brain ◽  
Late Gestation ◽  
High Rate ◽  
Emg Activity ◽  
Fetal Sheep ◽  
Progesterone Production ◽  
Progesterone Synthesis ◽  
Ovine Fetus ◽  
High Concentrations ◽  
Vascular Catheters

The high rate of progesterone synthesis by the placenta in late gestation exposes the ovine fetus to high concentrations of progesterone and its metabolites that may affect activity of the fetal brain. The aim of this study was to determine the effect of inhibiting maternal progesterone synthesis on sleep–wake activity in fetal sheep. Fetal and maternal vascular catheters, a fetal tracheal catheter, and electrodes for recording fetal electrocortical (ECoG), electro-ocular (EOG) and nuchal muscle electromyographic (EMG) activity were implanted. At 128–131 days gestation, progesterone production was inhibited by an injection of trilostane (50 mg), a 3β-hydroxysteroid dehydrogenase inhibitor. Vehicle solution or progesterone (3 mg h -1 ) was then infused into the ewe between 6 and 12 h after the trilostane treatment. Maternal progesterone concentrations were significantly reduced from 1–24 h after trilostane treatment (P < 0·05) when followed by vehicle infusion. Fetal breathing movements (FBM), EOG, nuchal muscle EMG, and behavioural arousal increased 12 h after trilostane treatment (P < 0 · 05). In contrast, there was no change in fetal arousal, EOG, EMG or FBM activities when progesterone was infused after the trilostane treatment. These findings show that progesterone can influence fetal behaviour, and indicates that normal progesterone production tonically suppresses arousal, or wakefulness in the fetus.

Divergent changes in plasma ACTH and pituitary POMC mRNA after cortisol administration to late-gestation ovine fetus

1998 ◽  
Vol 274 (3) ◽  
pp. E417-E425 ◽  
Author(s):  
T. M. Jeffray ◽  
S. G. Matthews ◽  
G. L. Hammond ◽  
J. R. G. Challis
Keyword(s):  
Plasma Cortisol ◽  
Late Gestation ◽  
Pars Intermedia ◽  
Mrna Levels ◽  
Plasma Acth ◽  
Negative Feedback Regulation ◽  
Fetal Sheep ◽  
Pomc Mrna ◽  
Free Cortisol ◽  
Ovine Fetus

Plasma concentrations of cortisol and adrenocorticotropic hormone (ACTH) rise in the late-gestation sheep fetus at approximately the same time as there is an increase in the plasma levels of corticosteroid- binding globulin (CBG). We hypothesized that intrafetal cortisol infusion during late pregnancy would stimulate an increase in fetal plasma CBG, which in turn would bind cortisol and diminish glucocorticoid negative-feedback regulation of the fetal pituitary, leading to an increase in plasma ACTH concentrations. Cortisol was infused into chronically catheterized fetal sheep beginning at 126.1 ± 0.5 days of gestation and continued for 96 h. Control fetuses were infused with saline. In cortisol-infused fetuses, the plasma cortisol concentrations rose significantly from control levels (4.4 ± 0.6 ng/ml) to 19.3 ± 3.1 ng/ml within 24 h and remained significantly elevated throughout the infusion period. Plasma immunoreactive (ir) ACTH concentrations were significantly elevated in cortisol-infused fetuses within 24–48 h and remained significantly higher than in controls throughout the 96-h experimental period. Plasma free cortisol concentrations increased 10-fold and remained significantly elevated in cortisol-infused animals, despite a rise in plasma corticosteroid-binding capacity. Levels of pituitary proopiomelanocortin (POMC) mRNA in the fetal pars distalis and pars intermedia were 96 and 38% lower, respectively, after 96 h of cortisol infusion. Therefore physiological elevations of plasma cortisol, in the late-gestation ovine fetus, lead to increases in mean plasma irACTH concentrations, but this is not associated with increases in fetal pituitary POMC mRNA levels.

Sympathoadrenal responses during hypoglycemia, hyperinsulinemia, and hypoxemia in the ovine fetus

1991 ◽  
Vol 261 (1) ◽  
pp. E95-E102 ◽  
Author(s):  
W. R. Cohen ◽  
G. J. Piasecki ◽  
H. E. Cohn ◽  
J. B. Susa ◽  
B. T. Jackson
Keyword(s):  
Insulin Infusion ◽  
Plasma Concentrations ◽  
Sympathetic Nerves ◽  
Significant Rise ◽  
Late Gestation ◽  
Plasma Catecholamine ◽  
Fetal Sheep ◽  
Ovine Fetus ◽  
Per Se ◽  
Adrenal Secretion

Interrelations of sympathoadrenal function and changes in glucose and insulin homeostasis were studied in chronically cannulated late gestation fetal sheep. Catecholamine secretory rates (based on direct adrenal sampling) and plasma concentrations were determined in the fetus during 2 h of insulin-induced hypoglycemia, during a period of hypoxemia, and during hyperinsulinemia per se (i.e., without hypoglycemia). Fetal insulin infusion (5–10 mU.kg-1.min-1) resulted in hypoglycemia and a significant rise in secretion of epinephrine but not of norepinephrine. By contrast, fetal hypoxemia caused a prompt and significant increase in adrenal secretion of both norepinephrine and epinephrine. Changes in peripheral plasma catecholamine levels were usually, but not always, qualitatively similar to those in adrenal secretion; the latter was a far more sensitive indicator of adrenal function. Hyperinsulinemia per se caused no change in adrenal secretory rates or plasma concentrations of catecholamines. Nevertheless, insulin infusion caused a fetal tachycardia even in the absence of hypoglycemia and hypoxemia, suggesting either a direct effect on the heart or stimulation of sympathetic nerves.

Blood pressure and heart rate in the ovine fetus: ontogenic changes and effects of fetal adrenalectomy

1999 ◽  
Vol 276 (1) ◽  
pp. H248-H256 ◽  
Author(s):  
Nobuya Unno ◽  
Chi H. Wong ◽  
Susan L. Jenkins ◽  
Richard A. Wentworth ◽  
Xiu-Ying Ding ◽  
...  
Keyword(s):  
Blood Pressure ◽  
Heart Rate ◽  
Plasma Cortisol ◽  
Time Windows ◽  
Late Gestation ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Long Term Study ◽  
Arterial Blood ◽  
Ovine Fetus

Ontogenic changes in baseline and 24-h rhythms of fetal arterial blood pressure (FABP) and heart rate (FHR) and their regulation by the fetal adrenal were studied in 18 fetal sheep chronically instrumented at 109–114 days gestation (GA). In the long-term study, FABP and FHR were continuously recorded from 120 days GA to spontaneous term labor (>145 days GA) in five animals. Peak times (PT) and amplitudes (Amp) of cosinor analysis were compared at 120–126, 127–133, and 134–140 days GA. Consistent, significant linear increases in FABP and linear decreases in FHR were observed in all fetuses. Significant 24-h rhythms in FABP and FHR were observed during all the time windows. In the adrenalectomy study, to test the hypothesis that fetal cortisol plays a key role in cardiovascular maturation, fetal adrenals were removed in eight animals (ADX); sham fetal adrenalectomy was performed on five animals (Con). Cortisol (4 μg/min) was infused intravenously in four ADX fetuses from day 7postsurgery for 7 days (ADX+F). No significant changes in PT and Amp in FABP and FHR were observed. Plasma cortisol levels remained low in Con and ADX fetuses (<4.9 ng/ml). Cortisol infusion increased fetal plasma cortisol to 22.3 ± 3.2 ng/ml (mean ± SE) on day 13 in ADX+F fetuses. FABP increased in control and ADX+F but not ADX fetuses; FHR decreased in control and ADX but rose in ADX+F fetuses. These results suggest that, in chronically instrumented fetal sheep at late gestation, 1) increases in FABP and decreases in FHR are maintained consistently from 120 to 140 days GA, with distinct 24-h rhythms, the PT and Amp of which remain unchanged, and 2) the physiological increase in FABP is dependent on the fetal adrenal; bilateral removal of the fetal adrenals does not prevent the ability of cortisol to produce a sustained increase in FABP.

Effect of hyperinsulinemia on amino acid utilization in the ovine fetus

2000 ◽  
Vol 279 (6) ◽  
pp. E1294-E1304 ◽  
Author(s):  
Patti J. Thureen ◽  
Bryan Scheer ◽  
Susan M. Anderson ◽  
Janet A. Tooze ◽  
David A. Young ◽  
...  
Keyword(s):  
Amino Acid ◽  
Nitrogen Utilization ◽  
Late Gestation ◽  
Amino Acid Solution ◽  
Fetal Sheep ◽  
Amino Acid Utilization ◽  
Lysine Concentration ◽  
Ovine Fetus ◽  
Nitrogen Uptake Rate ◽  
Amino Acid Concentrations

We studied the effect of an acute 4-h period of hyperinsulinemia (H) on net utilization rates (AAURnet) of 21 amino acids (AA) in 17 studies performed in 13 late-gestation fetal sheep by use of a novel fetal hyperinsulinemic-euglycemic-euaminoacidemic clamp. During H [84 ± 12 (SE) μU/ml H, 15 ± 2 μU/ml control (C), P < 0.00001], euglycemia was maintained by glucose clamp (19 ± 0.05 μmol/ml H, 1.19 ± 0.04 μmol/ml C), and euaminoacidemia (mean 4.1 ± 3.3% increase for all amino acid concentrations [AA], nonsignificantly different from zero) was maintained with a mixed amino acid solution adjusted to keep lysine concentration constant and other [AA] near C values. H produced a 63.7% increase in AAURnet (3.29 ± 0.66 μmol · min−1 · kg−1 H, 2.01 ± 0.55 μmol · min−1 · kg−1 C, P < 0.001), accounting for a 60.1% increase in fetal nitrogen uptake rate (2,064 ± 108 mg · day−1 · kg−1 H, 1,289 ± 73 mg · day−1 · kg−1 C, P < 0.001). Mean AA clearance rate (AAURnet/[AA]) increased by 64.5 ± 18.9% ( P < 0.001). Thus acute physiological H increases net amino acid and nitrogen utilization rates in the ovine fetus independent of plasma glucose and [AA].

Fetal fluid responses to long-term 5 M NaCl infusion: where does all the salt go?

1991 ◽  
Vol 261 (2) ◽  
pp. R412-R419 ◽  
Author(s):  
T. L. Powell ◽  
R. A. Brace
Keyword(s):  
Capillary Permeability ◽  
Water Movement ◽  
Allantoic Fluid ◽  
Late Gestation ◽  
Electrolyte Balance ◽  
Osmotic Gradient ◽  
Concentration Gradients ◽  
Fetal Sheep ◽  
Fetal Plasma

The fetus must obtain Na and Cl ions in order to grow. However, the regulation of electrolyte acquisition by the fetus is not well understood. To explore fetal electrolyte balance, we intravenously infused 5 M NaCl at a rate equal to 80% of the total fetal body Na+ and Cl- content per day (240 mM/day) for 3 days into late-gestation fetal sheep. We hypothesized that the increase in fetal osmolality resulting from the infusion would cause a transplacental water movement into the fetal compartment, leading to hydrops fetalis and/or polyhydramnios. The fetal-to-maternal osmotic gradient was initially -2.8 +/- 0.9 (SE) mosmol/kgH2O and rose by 4.8 +/- 1.8 mosmol/kgH2O during the infusion. Fetal plasma [Na+] and [Cl-] increased (3.0 +/- 0.4 and 5.5 +/- 0.5 meq/l, respectively), but the normal maternal-to-fetal transplacental concentration gradients for these ions were not reversed. Most of the infused Na+ (92 +/- 14%) and Cl- (82 +/- 12%) was excreted by the fetus in large volumes of hypotonic urine. Amniotic fluid osmolality and [Na+] were unchanged, but amniotic [Cl-] increased 5.7 +/- 2.4 meq/l. The amniotic plus allantoic fluid volume, as estimated by ultrasonography, was increased (43.5 +/- 14.5%) at day 2 and returned to control by day 3 of infusion. There was no fetal edema during the study or at autopsy. In light of these results, we propose a novel and somewhat complex mechanism for transplacental fluid and electrolyte movement in which placental capillary permeability increases along the length of the capillary.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term hypoxia modulates expression of key genes regulating adipose function in the late-gestation ovine fetus

2008 ◽  
Vol 294 (4) ◽  
pp. R1312-R1318 ◽  
Author(s):  
Dean A. Myers ◽  
Krista Hanson ◽  
Malgorzata Mlynarczyk ◽  
Kanchan M. Kaushal ◽  
Charles A. Ducsay
Keyword(s):  
Adipose Tissue ◽  
Uncoupling Protein ◽  
Late Gestation ◽  
Peroxisome Proliferator ◽  
Local Synthesis ◽  
Major Function ◽  
Ovine Fetus ◽  
Key Genes

A major function of abdominal adipose in the newborn is nonshivering thermogenesis. Uncoupling protein (UCP) UCP1 and UCP2 play major roles in thermogenesis. The present study tested the hypothesis that long-term hypoxia (LTH) modulates expression of UCP1 and UCP2, and key genes regulating expression of these genes in the late-gestation ovine fetus. Ewes were maintained at high altitude (3,820 m) from 30 to 138 days gestation (dG); perirenal adipose tissue was collected from LTH and age-matched, normoxic control fetuses at 139–141 dG. Quantitative real-time PCR was used to analyze mRNA for UCP1, UCP2, 11β hydroxysteroid dehydrogenase type 1 (HSD11B1) and 2 (HSD11B2), glucocorticoid receptor (GR), β3 adrenergic receptor (β3AR), deiodinase type 1 (DIO1) and DIO2, peroxisome proliferator activated receptor (PPAR) α and γ and PPARγ coactivator 1 (PGC1α). Concentrations of mRNA for UCP1, HSD11B1, PPARγ, PGC1, DIO1, and DIO2 were significantly higher in perirenal adipose of LTH compared with control fetuses, while mRNA for HSD11B2, GR, or PPARα in perirenal adipose did not differ between control and LTH fetuses. The increased expression of UCP1 is likely an adaptive response to LTH, assuring adequate thermogenesis in the event of birth under oxygen-limiting conditions. Because both glucocorticoids and thyroid hormone regulate UCP1 expression, the increase in HSD11B1, DIO1, and DIO2 implicate increased adipose capacity for local synthesis of these hormones. PPARγ and its coactivator may provide an underlying mechanism via which LTH alters development of the fetal adipocyte. These findings have important implications regarding fetal/neonatal adipose tissue function in response to LTH.

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