Validation of a specific radioimmunoassay to measure plasma cortisol in the fetal sheep

Pulmonary surfactant is synthesized by type II alveolar epithelial cells to regulate the surface tension at the air-liquid interface of the air-breathing lung. Developmental maturation of the surfactant system is controlled by many factors including oxygen, glucose, catecholamines, and cortisol. The intrauterine growth-restricted (IUGR) fetus is hypoxemic and hypoglycemic, with elevated plasma catecholamine and cortisol concentrations. The impact of IUGR on surfactant maturation is unclear. Here we investigate the expression of surfactant protein (SP) A, B, and C in lung tissue of fetal sheep at 133 and 141 days of gestation (term 150 ± 3 days) from control and carunclectomized Merino ewes. Placentally restricted (PR) fetuses had a body weight <2 SD from the mean of control fetuses and a mean gestational PaO2<17 mmHg. PR fetuses had reduced absolute, but not relative, lung weight, decreased plasma glucose concentration, and increased plasma cortisol concentration. Lung SP-A, -B, and -C protein and mRNA expression was reduced in PR compared with control fetuses at both ages. SP-B and -C but not SP-A mRNA expression and SP-A but not SP-B or -C protein expression increased with gestational age. Mean gestational PaO2was positively correlated with SP-A, -B, and -C protein and SP-B and -C mRNA expression in the younger cohort. SP-A and -B gene expression was inversely related to plasma cortisol concentration. Placental restriction, leading to chronic hypoxemia and hypercortisolemia in the carunclectomy model, results in significant inhibition of surfactant maturation. These data suggest that IUGR fetuses are at significant risk of lung complications, especially if born prematurely.

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Effects of thyroid hormones on pulmonary and renal angiotensin-converting enzyme concentrations in fetal sheep near term

Journal of Endocrinology ◽

10.1677/joe.0.1730143 ◽

2002 ◽

Vol 173 (1) ◽

pp. 143-150 ◽

Cited By ~ 13

Author(s):

AJ Forhead ◽

AL Fowden

Keyword(s):

Angiotensin Converting Enzyme ◽

Thyroid Hormones ◽

Plasma Cortisol ◽

Experimental Manipulation ◽

Late Gestation ◽

Converting Enzyme ◽

Fetal Sheep ◽

Near Term ◽

Sheep Fetus

In the sheep fetus, pulmonary and renal concentrations of angiotensin-converting enzyme (ACE) increase towards term in parallel with the prepartum surges in plasma cortisol and tri-iodothyronine (T(3)). The ontogenic change in pulmonary ACE has been shown to be induced, at least in part, by cortisol but the role of the thyroid hormones is unknown. Therefore, this study investigated the effects of thyroid hormones on tissue ACE concentration in fetal sheep during late gestation. Pulmonary and renal ACE concentrations were measured in sheep fetuses after experimental manipulation of thyroid hormone status by fetal thyroidectomy and exogenous hormone infusion. In intact fetuses, pulmonary and renal ACE concentrations increased between 127-132 and 142-145 days of gestation (term 145 +/- 2 days), coincident with the prepartum rises in plasma cortisol and T(3). The ontogenic increment in pulmonary ACE concentration was abolished when the prepartum surge in T(3), but not cortisol, was prevented by fetal thyroidectomy. At 143-145 days, ACE concentration in the lungs and kidneys of the thyroidectomised fetuses were both lower than those in the intact fetuses. In intact fetuses at 127-132 days, pulmonary ACE was upregulated by intravenous infusions of either cortisol (2-3 mg/kg per day) or T(3) (8-12 microg/kg per day) for 5 days. Renal ACE was unaffected by cortisol or T(3) infusion. Therefore, thyroid hormones have an important role in the developmental control of pulmonary and renal ACE concentration in the sheep fetus towards term. In addition, the prepartum rise in plasma T(3) appears to mediate, in part, the maturational effect of cortisol on pulmonary ACE concentration.

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

AJP Endocrinology and Metabolism ◽

10.1152/ajpendo.1998.274.3.e417 ◽

1998 ◽

Vol 274 (3) ◽

pp. E417-E425 ◽

Cited By ~ 3

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.

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Effects of elevated fetal cortisol concentrations on the volume, secretion, and reabsorption of lung liquid

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1995.269.4.r881 ◽

1995 ◽

Vol 269 (4) ◽

pp. R881-R887 ◽

Cited By ~ 9

Author(s):

M. J. Wallace ◽

S. B. Hooper ◽

R. Harding

Keyword(s):

Plasma Cortisol ◽

Fetal Lung ◽

Liquid Volume ◽

Fetal Sheep ◽

Fetal Plasma ◽

Age Related ◽

Lung Liquid ◽

Secretion Rates ◽

Related Increase

We have examined the role of cortisol in the gestational age-related increase in the ability of epinephrine to inhibit the secretion and induce the reabsorption of fetal lung liquid. Chronically catheterized fetal sheep were infused with either saline (n = 6) or increasing doses of cortisol (1.5-3.5 mg/day; n = 6) between 120 and 130 days of gestation (term approximately 145 days). Lung liquid volumes and secretion rates were measured at 120 days (before infusion) and at 125 days, and then at 130 days we tested the ability of epinephrine to inhibit lung liquid secretion and induce liquid reabsorption. Cortisol infusions increased fetal plasma cortisol and 3,5,3'-triiodothyronine (T3) concentrations to levels observed just before labor and significantly increased the age-related increase in fetal lung liquid volume and secretion rate. At 130 days, epinephrine caused a significantly greater rate of lung liquid reabsorption in cortisol-infused fetuses (10.3 +/- 2.3 ml/h) than in saline-infused fetuses (1.5 +/- 1.6 ml/h). We conclude that a premature elevation in circulating fetal cortisol concentrations, probably in conjunction with elevated T3 concentrations, prematurely increases the epinephrine-induced reabsorption of fetal lung liquid. It is likely, therefore, that the preparturient increase of fetal cortisol concentrations plays an important role in the clearance of lung liquid at birth.

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Ontogeny and Effects of Hypothalamic Pituitary Disconnection on Formation of Inositol Trisphosphate in Fetal Sheep Pituitary Cells

Endocrinology ◽

10.1210/en.2006-1185 ◽

2007 ◽

Vol 148 (3) ◽

pp. 1440-1444 ◽

Cited By ~ 3

Author(s):

Luke C. Carey ◽

Stephen B. Tatter ◽

James C. Rose

Keyword(s):

Gestational Age ◽

Plasma Cortisol ◽

Inositol Trisphosphate ◽

Second Messenger ◽

Late Gestation ◽

Pituitary Cells ◽

Fetal Sheep ◽

The Impact ◽

Pituitary Adrenal Axis ◽

Sheep Fetus

In late gestation fetal sheep, the pituitary becomes increasingly responsive to stimulation by arginine vasopressin (AVP). This change appears to be one important factor mediating the plasma cortisol surge, a critical developmental event. It is not known precisely why pituitary corticotropes become more responsive at this time. In this study we examined the possibility that changes in second messenger generation [inositol trisphosphate (IP3)] are responsible. Two studies were undertaken. The first was an ontogeny study, where pituitaries were isolated from 100-, 120-, and 140-d gestational age (dGA) fetal sheep. Cells were cultured, stimulated with AVP, and the formation of IP3 assessed. The amount of IP3 generated increased with gestational age (percent increases from unstimulated controls were 4.6, 11.5, and 21.5 for 100, 120, and 140 dGA, respectively), with significant differences between the 140-dGA group and both earlier groups apparent. The second study examined the impact of 120-dGA hypothalamo-pituitary disconnection (HPD), which prevents corticotrope maturation, on responsiveness of pituitary cells isolated from 140-dGA fetuses. Cells were stimulated with AVP, and the formation of IP3 and secretion of ACTH were assessed. Significantly less IP3 was formed, and ACTH secreted in cells from HPD compared with control fetuses (IP3 and ACTH levels were 50% and 35% lower, respectively). Results from the HPD study demonstrate that the ontogenic changes in IP3 after AVP require an intact hypothalamic-pituitary-adrenal axis. These findings suggest that heightened second messenger generation may be a key reason for increased ACTH secretory responsiveness to AVP in the late gestation sheep fetus.

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Subclinical exposure to low-dose endotoxin impairs EEG maturation in preterm fetal sheep

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00216.2012 ◽

2012 ◽

Vol 303 (3) ◽

pp. R270-R278 ◽

Cited By ~ 29

Author(s):

Michael J. Keogh ◽

Laura Bennet ◽

Paul P. Drury ◽

Lindsea C. Booth ◽

Sam Mathai ◽

...

Keyword(s):

White Matter ◽

Plasma Cortisol ◽

Low Dose ◽

Blood Gases ◽

Power Spectral Analysis ◽

Periventricular White Matter ◽

Fetal Sheep ◽

Beta Power ◽

Dose Infusion ◽

Arterial Plasma

Exposure to chorioamnionitis is strongly associated with neurodevelopmental disability after premature birth; however, it remains unclear whether subclinical infection affects functional EEG maturation. Chronically instrumented 103–104-day-old (0.7 gestational age: term 147 days) fetal sheep in utero were randomized to receive either gram-negative LPS by continuous low-dose infusion (100 ng iv over 24 h, followed by 250 ng/24 h for 4 days; n = 6) or the same volume of normal saline ( n = 9). Arterial plasma cortisol, ACTH, and IL-6 were measured. The delta (0–3.9 Hz), theta (4–7.9 Hz), alpha (8–12.9 Hz), and beta (13–22 Hz) components of the EEG were determined by power spectral analysis. Brains were taken after 10 days for histopathology. There were no changes in blood gases, cardiovascular variables, or EEG power during LPS infusion, but a transient rise in plasma cortisol and IL-6 ( P < 0.05). LPS infusion was associated with loss of the maturational increase to higher frequency activity, with reduced alpha and beta power, and greater delta power than saline controls from 6 to 10 days ( P < 0.05). Histologically, LPS was associated with increased numbers of microglia and TNF-α-positive cells in the periventricular white matter and frontoparietal cortex, increased caspase-3-positive cells in white matter, but no loss of CNPase-positive oligodendrocytes, Nurr-1 subplate cells, or gyral complexity. These data suggest that low-dose endotoxin exposure can impair EEG maturation in preterm fetal sheep in association with neural inflammation but without hemodynamic disturbances or cortical injury.

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Time-Trend Analysis of Plasma Cortisol Concentrations in the Fetal Sheep in Relation to Parturition*

Endocrinology ◽

10.1210/endo-107-1-155 ◽

1980 ◽

Vol 107 (1) ◽

pp. 155-159 ◽

Cited By ~ 113

Author(s):

D. M. MAGYAR ◽

D. FRIDSHAL ◽

C. W. ELSNER ◽

T. GLATZ ◽

J. ELIOT ◽

...

Keyword(s):

Trend Analysis ◽

Plasma Cortisol ◽

Time Trend ◽

Fetal Sheep

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

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.1.h248 ◽

1999 ◽

Vol 276 (1) ◽

pp. H248-H256 ◽

Cited By ~ 16

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.

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Changes in surfactant-associated protein mRNA profile in growth-restricted fetal sheep

AJP Lung Cellular and Molecular Physiology ◽

10.1152/ajplung.1999.276.3.l459 ◽

1999 ◽

Vol 276 (3) ◽

pp. L459-L465 ◽

Cited By ~ 16

Author(s):

Robert Gagnon ◽

Johnathan Langridge ◽

Kevin Inchley ◽

Jun Murotsuki ◽

Fred Possmayer

Keyword(s):

Fetal Growth ◽

Fetal Growth Restriction ◽

Plasma Cortisol ◽

Fold Increase ◽

Fetal Lung ◽

Placental Insufficiency ◽

Control Group ◽

Fetal Sheep ◽

Tissue Levels ◽

Fetal Plasma

To test the hypothesis that chronic placental insufficiency resulting in fetal growth restriction causes an increase in fetal lung surfactant-associated protein (SP) gene expression, we embolized chronically catheterized fetal sheep ( n = 6) daily using nonradioactive microspheres in the abdominal aorta for 21 days (between 0.74 and 0.88 of gestation) until fetal arterial oxygen content was reduced by ∼40–50%. Control animals ( n = 7) received saline only. Basal fetal plasma cortisol concentration was monitored. At the end of the experiment, fetal lung tissues were collected, and ratios of tissue levels of SP-A, SP-B, and SP-C mRNA to 18S rRNA were determined by standard Northern blot analysis. Total DNA content of fetal lungs was reduced by 30% in the embolized group compared with control group ( P = 0.01). There was a 2.7-fold increase in fetal lung SP-A mRNA ( P< 0.05) and a 3.2-fold increase in SP-B mRNA ( P < 0.01) in the chronically embolized group compared with those in the control group. SP-A and SP-B mRNA tissue levels were highly correlated with the mean fetal plasma cortisol levels on days 20–21( r = 0.90, P < 0.01 for SP-A mRNA and r = 0.94, P < 0.01 for SP-B mRNA). SP-C mRNA tissue levels were not significantly affected by placental insufficiency. We conclude that fetal growth restriction due to placental insufficiency is associated with alterations in fetal lung SP, suggesting enhanced lung maturation that was highly dependent on the degree of increase in fetal plasma cortisol levels.

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Are fetal adrenocorticotropic hormone and renin secretion suppressed by maternal cortisol secretion?

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1988.255.3.r412 ◽

1988 ◽

Vol 255 (3) ◽

pp. R412-R417 ◽

Cited By ~ 3

Author(s):

C. E. Wood

Keyword(s):

Plasma Cortisol ◽

Adrenocorticotropic Hormone ◽

Plasma Concentrations ◽

Plasma Renin ◽

Maternal Plasma ◽

Renin Secretion ◽

Plasma Acth ◽

Fetal Sheep ◽

Fetal Plasma ◽

Adrenal Secretion

Previous studies from this laboratory have demonstrated that intravenous infusions of hydrocortisone (cortisol) into fetal sheep at rates that produce plasma concentrations achieved during fetal stress inhibit fetal adrenocorticotropic hormone (ACTH) and renin secretion. The present study was designed to test for inhibition of fetal renin and ACTH after maternal adrenal secretion of cortisol. ACTH-(1-24) or saline infusion into 12 pregnant ewes (120-132 days gestation) at rates of 0, 1, 5, or 20 ng ACTH.kg-1.min-1 for 5 h produced dose-related increases in maternal plasma ACTH and cortisol concentrations and fetal plasma cortisol concentration. In the 20-ng.kg-1.min-1 group, increases in fetal plasma cortisol of 8.0 ng/ml (to 24.3 +/- 3.7 ng/ml) did not suppress basal fetal plasma renin activity. One hour after the end of the maternal vehicle or ACTH infusion, fetal ACTH secretion was stimulated by fetal intravenous infusion of sodium nitroprusside. In the 0-, 1-, and 5-ng.kg-1.min-1 groups, fetal ACTH responses to nitroprusside were suppressed in animals infused with ACTH. Together, these results indicate that the maternal adrenal secretion of cortisol inhibits stimulated secretion of ACTH but not renin in 120- to 132-day-gestation fetal sheep.

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