Levels of pro-opiomelanocortin and prolactin mRNA in the fetal sheep pituitary following hypoxaemia and glucocorticoid treatment in late gestation

1995 ◽  
Vol 147 (1) ◽  
pp. 139-146 ◽  
Author(s):  
S G Matthews ◽  
J R G Challis
Keyword(s):  
Late Gestation ◽  
Pars Intermedia ◽  
Mrna Levels ◽  
Glucocorticoid Treatment ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Pomc Mrna ◽  
Highly Sensitive ◽  
Ovine Fetal

Abstract It is well established that corticotrophin-releasing hormone and vasopressin can induce both synthesis and release of ACTH from the ovine pituitary gland, and that glucocorticoids can inhibit these responses. Changes in the abundance, localization and distribution of proopiomelanocortin (POMC) mRNA and prolactin (PRL) mRNA in the ovine fetal pituitary were examined by in situ hybridization following hypoxaemia applied in the presence or absence of concomitant cortisol in late gestation (day 135). Fetuses were distributed amongst four groups; saline-infused/normoxaemic, cortisol-infused/normoxaemic (0·3 mg/h), saline-infused/hypoxaemic and cortisol-infused/hypoxaemic. Hypoxaemia (6 h) was induced by reducing the maternal PaO2, resulting in a 6–8 mmHg decrease in fetal arterial PO2. Fetal infusions were commenced 5 h prior to and maintained throughout the treatment period. Hypoxaemia, which elevated fetal plasma ACTH and cortisol, caused a significant (P<0·05) increase in POMC mRNA in the pars distalis (PD), but was without effect on POMC mRNA in the pars intermedia (PI). Cortisol infusion attenuated the hypoxaemiainduced increase in POMC mRNA in the PD, but was without effect on non-stimulated steady-state POMC mRNA levels in either the PD or PI. PRL mRNA was only present in the PD and significantly (P<0·05) increased after cortisol infusion and hypoxaemia. In conclusion (i) POMC and PRL mRNA in the PD are increased following moderate hypoxaemia, (ii) cortisol attenuates changes in POMC mRNA but not PRL mRNA in the PD following hypoxaemia and (iii) cortisol increases PRL mRNA levels in the PD. Synthesis of POMC and PRL in the fetal PD is highly sensitive to homeostatic perturbations and glucocorticoids in late gestation. Journal of Endocrinology (1995) 147, 139–146

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.

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.

Effects of long-term hypoxemia on pituitary-adrenal function in fetal sheep

1996 ◽  
Vol 271 (4) ◽  
pp. E678-E685 ◽  
Author(s):  
J. Murotsuki ◽  
R. Gagnon ◽  
S. G. Matthews ◽  
J. R. Challis
Keyword(s):  
Adrenal Function ◽  
Arterial Oxygen ◽  
Pars Intermedia ◽  
Mrna Levels ◽  
Pars Distalis ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Pomc Mrna ◽  
Pregnant Sheep

To test the hypothesis that long-term hypoxemia causes premature activation of the fetal pituitary-adrenal function, we embolized the fetal side of the placenta in pregnant sheep and examined the changes in concentrations of immunoreactive adrenocorticotropic hormone (irACTH), cortisol, and prostaglandin E2 (PGE2) in fetal plasma, and levels and localization of proopiomelanocortin (POMC) mRNA in the pars distalis and the pars intermedia of the fetal pituitary. Twelve fetal sheep were studied (6 embolized and 6 control) for 21 days between 0.74 and 0.88 of gestation. Daily injections of nonradiolabeled microspheres were given into the fetal abdominal aorta to decrease fetal arterial oxygen content by 40-50% of the preembolization values. In the embolized group, concentrations of irACTH, PGE2, and cortisol in fetal plasma increased gradually and were significantly (P < 0.05) elevated above those of controls after day 10, day 16, and day 20, respectively. POMC mRNA levels in the pars distalis of the fetal pituitary were not different from those of controls but were significantly reduced in the pars intermedia (P < 0.05). We conclude that levels of POMC mRNA in the pars distalis are unchanged during long-term hypoxemia possibly because of negative feedback effects of elevated cortisol on the pituitary gland. During long-term fetal hypoxemia, there is a differential regulation of POMC mRNA expression in the pars distalis and pars intermedia.

Pro-opiomelanocortin messenger RNA levels increase in the fetal sheep pituitary during late gestation

1991 ◽  
Vol 131 (3) ◽  
pp. 483-489 ◽  
Author(s):  
K. Yang ◽  
J. R. G. Challis ◽  
V. K. M. Han ◽  
G. L. Hammond
Keyword(s):  
Messenger Rna ◽  
Blot Hybridization ◽  
Late Gestation ◽  
Northern Blot Hybridization ◽  
Mrna Levels ◽  
Plasma Acth ◽  
Mrna Accumulation ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Pomc Mrna

ABSTRACT Plasma levels of ACTH and cortisol in fetal sheep increase progressively during late pregnancy, providing the stimulus for birth. However, little information is available concerning either sources of pro-opiomelanocortin (POMC, the precursor to ACTH) or changes in POMC gene expression, which may be responsible for the elevated fetal plasma ACTH concentrations. We therefore studied the relative amount of POMC mRNA in fetal sheep hypothalami, anterior pituitaries and adrenals at discrete times of pregnancy between day 60 and term (approximately 145 days) and from newborn lambs. Total RNA from these tissues was analysed by Northern blot hybridization using a human POMC DNA probe, and the amount of POMC mRNA was expressed relative to the signal obtained for 18S ribosomal RNA. A single 1·2 kb transcript was detected by day 60 in the anterior pituitary, and its relative amount did not change significantly until after days 125–130. Pituitary POMC mRNA levels increased significantly at days 138–143, remained elevated at term and increased further in newborn lambs. In contrast, POMC mRNA was undetectable in hypothalami and adrenal glands of fetuses at all ages. The results suggested that the prepartum rise in plasma ACTH concentrations in fetal sheep is due to increased POMC biosynthesis in the fetal pituitary. The increase in POMC mRNA occurs at a time when fetal plasma cortisol concentrations are elevated, indicating that the negative feedback effects of circulating glucocorticoids on the fetal hypothalamicpituitary axis may be obscured by other mechanisms that increase pituitary POMC mRNA accumulation during the last week of gestation. Journal of Endocrinology (1991) 131, 483–489

scholarly journals Subpopulations of Corticotrophs in the Sheep Pituitary during Late Gestation: Effects of Development and Placental Restriction

Endocrinology ◽  
2006 ◽  
Vol 147 (10) ◽  
pp. 4762-4771 ◽  
Author(s):  
Kirsten Farrand ◽  
I. Caroline McMillen ◽  
Shigeyasu Tanaka ◽  
Jeffrey Schwartz
Keyword(s):  
Late Gestation ◽  
Mrna Levels ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Pomc Mrna ◽  
Experimental Induction ◽  
Attachment Sites ◽  
Specific Antisera

The prepartum surge in fetal plasma cortisol is essential for the normal timing of parturition in sheep and may result from an increase in the ratio of ACTH to proopiomelanocortin (POMC) in the fetal circulation. In fetuses subjected to experimental induction of placental restriction, the prepartum surge in fetal cortisol is exaggerated, whereas pituitary POMC mRNA levels are decreased, and in vitro, unstimulated ACTH secretion is elevated in corticotrophs nonresponsive to CRH. We therefore investigated the changes in the relative proportions of cells expressing POMC, ACTH, and the CRH type 1 receptor (CRHR1) shortly before birth and during chronic placental insufficiency. Placental restriction (PR) was induced by removal of the majority of placental attachment sites in five ewes before mating. Pituitaries were collected from control and PR fetal sheep at 140 d (control, n = 4; PR, n = 4) and 144 d (control, n = 6; PR, n = 4). Pituitary sections were labeled with specific antisera raised against POMC, ACTH, and CRHR1. Three major subpopulations of corticotrophs were identified that expressed POMC + ACTH + CRHR1, ACTH + CRHR1, or POMC only. The proportion of pituitary corticotrophs expressing POMC + ACTH + CRHR1 decreased (P &lt; 0.05) between 140 (control, 60 ± 1%; PR, 66 ± 4%) and 144 (control, 45 ± 2%; PR, 56 ± 6%) d. A significantly higher (P &lt; 0.05) proportion of corticotrophs expressed POMC + ACTH + CRHR1 in the pituitary of the PR group compared with controls. This study is the first to demonstrate subpopulations of corticotrophs in the fetal sheep pituitary that differentially express POMC, ACTH, and CRHR1 and the separate effects of gestational age and placental restriction on these subpopulations of corticotrophs.

Developmental changes in the distribution of pro-opiomelanocortin and prolactin mRNA in the pituitary of the ovine fetus and lamb

1994 ◽  
Vol 13 (2) ◽  
pp. 175-185 ◽  
Author(s):  
S G Matthews ◽  
X Han ◽  
F Lu ◽  
J R G Challis
Keyword(s):  
Late Gestation ◽  
Pars Intermedia ◽  
Fetal Life ◽  
Mrna Levels ◽  
Pars Distalis ◽  
Pomc Mrna ◽  
Inferior Aspect ◽  
Ovine Fetus ◽  
Pomc Gene

ABSTRACT Ontogenic changes in pituitary pro-opiomelanocortin (POMC) mRNA and prolactin (PRL) mRNA were examined during gestation and early neonatal life using in situ hybridization histochemistry. Pituitaries were harvested from fetuses at days 60–80, 100–120, 135–140 and 142–143 of gestation and at term, and from lambs at days 1–7 and 30–60 of age and adults. POMC mRNA, present by day 60, rose during mid- and late gestation. Concurrently there was a change in corticotroph distribution, resulting in a relatively greater quantity of POMC mRNA at the base of the pars distalis. At term, there was a significant (P<0·05) further elevation of POMC mRNA. POMC mRNA levels remained high in the newborn lamb but decreased in the adult. Cells in the pars intermedia expressed large amounts of POMC mRNA early in fetal life and this pattern persisted throughout gestation and into the neonatal period. Changes in the expression of the POMC gene correlated closely with the presence of immunoreactive (ir)ACTH in the pituitary; in fetuses the proportion of irACTH-positive cells rose to 10% of pars distalis cells by day 100 and did not change significantly thereafter. The lactotrophs contained PRL mRNA by day 60, and the quantity increased towards parturition (P<0·05). PRL mRNA subsequently decreased in the neonate, but rose as the lamb matured. These results indicate that in the fetal pituitary: (1) the POMC gene is highly expressed during gestation in both the pars distalis and the pars intermedia, (2) changes in the amounts of POMC mRNA and PRL mRNA in the pars distalis correlate with the distribution of irACTH and irPRL respectively, and (3) POMC mRNA is distributed primarily in the inferior aspect of the pars distalis, and in this region its quantity is highest immediately prior to parturition.

Ontogeny and effect of cortisol on vasopressin-1b receptor expression in anterior pituitaries of fetal sheep

2003 ◽  
Vol 284 (1) ◽  
pp. R51-R56 ◽  
Author(s):  
Sharla F. Young ◽  
Jennifer L. Smith ◽  
Jorge P. Figueroa ◽  
James C. Rose
Keyword(s):  
Receptor Expression ◽  
Late Gestation ◽  
Mrna Levels ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Protein Levels ◽  
Receptor Mrna ◽  
Naturally Occurring ◽  
V1b Receptor

Corticotroph responsiveness to arginine vasopressin (AVP) increases during late gestation in fetal sheep. The mechanism of this increase in AVP responsiveness is currently unknown but could be related to an increase in vasopressin type 1b (V1b) receptor expression in the pituitary during development. To determine if there are ontogenic changes in V1b receptor expression that may help explain the changes in ACTH responses to AVP, we studied pituitaries from three groups of fetal sheep [100, 120, or 140 days gestational age (dGA)]. V1b receptor mRNA and protein significantly decreased by 140 dGA. Peak V1b mRNA levels were detected at 100 dGA, while peak V1b protein levels were detected at 120 dGA. The reduction in V1b receptor expression in late gestation may be due to the naturally occurring peripartum increase in fetal plasma cortisol because cortisol infusion at 122–130 dGA decreased V1b receptor mRNA. Thus there is a marked decrease in the expression of the V1b receptor in the pituitary during fetal development, leaving the role of the V1b receptor in increasing AVP responsiveness uncertain.

Infusion of ACTH stimulates expression of adrenal ACTH receptor and steroidogenic acute regulatory protein mRNA in fetal sheep

2006 ◽  
Vol 291 (2) ◽  
pp. E214-E220 ◽  
Author(s):  
Luke C. Carey ◽  
Yixin Su ◽  
Nancy K. Valego ◽  
James C. Rose
Keyword(s):  
Regulatory Protein ◽  
Late Gestation ◽  
Mrna Levels ◽  
Acth Stimulation ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Arterial Blood ◽  
Acth Receptor ◽  
Underlying Mechanisms

The late-gestation plasma cortisol surge in the sheep fetus is critical for stimulating organ development and parturition. Increased adrenal responsiveness is one of the key reasons for the surge; however, the underlying mechanisms are not fully understood. Our recent studies suggest that ACTH-mediated increased expression of ACTH receptor (ACTH-R) and steroid acute regulatory protein (StAR) may play a role in enhancing responsiveness. Hence, we examined effects of ACTH infusion in fetal sheep on mRNA expression of these two mediators of adrenal responsiveness and assessed the functional consequences of this treatment in vitro. Fetuses of ∼118 and 138 days of gestational age (dGA) were infused with ACTH-(1–24) for 24 h. Controls received saline infusion. Arterial blood was sampled throughout the infusion. Adrenals were isolated and analyzed for ACTH-R and StAR mRNA, or cells were cultured for 48 h. Cells were stimulated with ACTH, and medium was collected for cortisol measurement. Fetal plasma ACTH and cortisol concentrations increased over the infusion period in both groups. ACTH-R mRNA levels were significantly higher in ACTH-infused fetuses in both the 118 and 138 dGA groups. StAR mRNA increased significantly in both the 118 and 138 dGA groups. Adrenal cells from ACTH-infused fetuses were significantly more responsive to ACTH stimulation in terms of cortisol secretion than those from saline-infused controls. These findings demonstrate that increases in circulating ACTH levels promote increased expression of ACTH-R and StAR mRNA and are coupled to heightened adrenal responsiveness.

Proopiomelanocortin, prolactin and growth hormone messenger ribonucleic acid levels in the fetal sheep pituitary during late gestation

1993 ◽  
Vol 129 (3) ◽  
pp. 263-267 ◽  
Author(s):  
Jennifer J Merei ◽  
Alix Rao ◽  
lain J Clarke ◽  
I Caroline McMillen
Keyword(s):  
Growth Hormone ◽  
Ribonucleic Acid ◽  
Late Gestation ◽  
Mrna Levels ◽  
Fetal Sheep ◽  
Messenger Ribonucleic Acid ◽  
Pomc Mrna ◽  
Significant Difference ◽  
The Mean ◽  
Pomc Gene

We have measured the relative levels of proopiomelanocortin (POMC), prolactin (PRL) and growth hormone (GH) messenger ribonucleic acid (mRNA) in the anterior and neurointermediate lobes of the fetal pituitary during the last 2–3 weeks of gestation. The mean POMC mRNA/18S RNA ratio in the fetal anterior pituitary was significantly greater (p<0.02) at 130–136 days (0.90±0.08; N=9) than at 141–143 days of gestation (0.67±0.07; N=6). In contrast, the mean PRL mRNA/18S RNA ratio increased significantly (p< 0.02) ) between 130 and 136 days (0.31±0.05; N = 9) when compared with 141–143 days of gestation (0.58±0.10; N = 6). There was no significant difference, however, between the mean GH mRNA/18S RNA ratio in fetal anterior pituitaries at 130–136 days (0.95±0.04; N = 9) when compared with 141–143 days of gestation (1.08±0.14; N=6). The POMC mRNA/18S RNA ratio in the neurointermediate lobes was seven-, five- and tenfold higher than in anterior pituitaries at 130–134, 135–136 and 141–143 days of gestation, respectively. We hypothesize that elevated circulating cortisol levels after 140 days of gestation act in the slow time domain (i.e. over days) to suppress POMC gene expression and that the increase in fetal pituitary PRL mRNA levels may be a consequence of oestrogen stimulation in late gestation.

Dopaminergic regulation of adrenocorticotrophic hormone, α-melanocyte-stimulating hormone and cortisol secretion in the ovine fetus

1996 ◽  
Vol 151 (3) ◽  
pp. 439-447 ◽  
Author(s):  
D M Hagan ◽  
A N Brooks
Keyword(s):  
Plasma Concentrations ◽  
Pars Intermedia ◽  
Dopamine Antagonist ◽  
Intermediate Lobe ◽  
Fetal Sheep ◽  
Fetal Plasma ◽  
Melanocyte Stimulating Hormone ◽  
Ovine Fetus ◽  
Dopaminergic Regulation ◽  
Ovine Fetal

Abstract During ovine fetal development there is a progressive maturation of the hypothalamo–pituitary–adrenal axis which culminates in the onset of birth. The role and regulation of the intermediate lobe of the fetal pituitary gland in relation to this maturational process remains controversial. To test the hypothesis that the pars intermedia of the ovine fetal pituitary is under tonic inhibitory dopaminergic control we treated fetal sheep at day 131 of gestation with a 3-day intravenous infusion of one of the following: the dopamine antagonist sulpiride (0·3 mg/0·5 ml/h; n=12), the dopamine agonist bromocriptine (0·03 mg/0·5 ml/h; n=7) or vehicle (0·1 m tartaric acid in saline; n=8) alone. Fetal plasma concentrations of α-MSH were significantly (P<0·01) increased by treatment with sulpiride and decreased (P<0·05) by bromocriptine. The increase in α-MSH after sulpiride was characterised by an increase in the amplitude of α-MSH pulses whereas bromocriptine virtually abolished all pulses of α-MSH. Immunoreactive ACTH (IR-ACTH) concentrations were significantly (P<0·05) elevated after sulpiride but were unaffected by bromocriptine. There were no changes in the pulsatile characteristics of IR-ACTH secretion. Cortisol concentrations were unchanged by either treatment. We conclude that fetal α-MSH and IR-ACTH are secreted in a pulsatile fashion and are tonically inhibited by dopaminergic pathways. The lack of an effect of endogenously raised α-MSH on plasma cortisol concentrations provides evidence that this POMC-derived peptide is not responsible for the regulation of cortisol biosynthesis and/or secretion. Journal of Endocrinology (1996) 151, 439–447

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