Catherine L. Coulter

Prenatal Undernutrition, Glucocorticoids And The Programming Of Adult Hypertension

1. A range of epidemiological studies has shown that poor intra‐uterine growth is associated with an increased prevalence of cardiovascular disease, non‐insulin‐dependent diabetes mellitus and the Metabolic syndrome in adult life.

Fetal adrenal development: insight gained from adrenal tumors

Precise and coordinated mechanisms control the growth and functional differentiation of fetal organ systems. Conversely, tumor progression and the development of cancer probably occur through a process of dysregulation and dedifferentiation. Similarities exist between normal human fetal adrenal cortex and adrenal cancers, such as high expression of growth factors, including insulin-like growth factor II. Therefore, we might gain insight into factors involved in adrenocortical development through better understanding the development and progression of adrenocortical tumors. This review is prompted by recent gene profiling studies that have identified genes differentially expressed between normal and abnormal adrenal glands. Several of these genes are specific growth factors or key cell cycle regulators, in addition to genes not previously associated with adrenal growth or function.

Early Embryonic Environment, The Fetal Pituitary‐Adrenal Axis and the Timing of Parturition

It is well established in the sheep, that the normal timing of parturition is dependent on a prepartum activation of the fetal pituitary‐adrenal axis. We have recently demonstrated for the first time that embryo number, embryo sex, and alterations in the environment of the early embryo, including exposure to maternal undernutrition during the periconceptional period, alter the timing and level of activation of the pituitary‐adrenal axis in the sheep fetus during late gestation. There is a delay in activation of the fetal HPA axis in twin fetuses and we speculate that the diminished adrenocortical responsiveness in the twin fetus may be an adaptive response, which counters the impact of the potential enhanced intrauterine stress experienced by a twin fetus, thereby reducing the possibility of preterm delivery. We have also reported that a moderate restriction of maternal nutrition to during the periconceptional period (from 60 days before and for one week after conception) resulted in an earlier activation of the pituitary‐adrenal axis of twin, but not singleton, fetuses during late gestation. A series of studies using assisted reproductive technologies have also found that perturbation of the early embryonic environment results in a dysregulation of placental and fetal growth and development and in the timing of normal parturition. In summary, after several decades of work focussed on events in late gestation associated with the prepartum activation and stress responsiveness of the fetal HPA axis, our recent studies indicate that the environment of the early embryo may have a significant role to play in determining the timing and level of the prepartum activation of this axis and potentially on the functional capacity of the axis to respond to acute or chronic stress in later life.

FUNCTIONAL BIOLOGY OF THE PRIMATE FETAL ADRENAL GLAND: ADVANCES IN TECHNOLOGY PROVIDE NEW INSIGHT

1. The main aim of the present review is to summarize recent experimental data from human and non‐human primate models that have identified factors essential for adrenal development and other factors that may determine the regulation of the specific structural organization and function of the adrenal gland.

Steroidogenic Acute Regulatory Protein Expression Is Decreased in the Adrenal Gland of the Growth-Restricted Sheep Fetus During Late Gestation

Abstract Functional development of the adrenal cortex is critical for fetal maturation and postnatal survival. In the present study, we have determined the developmental profile of expression of the mRNA and protein of an essential cholesterol-transporting protein, steroidogenic acute regulatory protein (StAR), in the adrenal of the sheep fetus. We have also investigated the effect of placental restriction (PR) on the expression of StAR mRNA and protein in the growth-restricted fetus. Adrenal glands were collected from fetal sheep at 82–91 days (n = 10), 125–133 days (n = 10), and 140–144 days (n = 9) and from PR fetuses at 141–145 days gestation (n = 9) (term = 147 ± 3 days gestation). The adrenal StAR mRNA:18S rRNA increased (P < 0.05) between 125 days (7.44 ± 1.61) and 141–144 days gestation (13.76 ± 1.88). There was also a 13-fold increase (P < 0.05) in the amount of adrenal StAR protein between 133 and 144 days gestation in these fetuses. However, the amount of StAR protein (6.9 ± 1.7 arbitrary densitometric units [AU]/μg adrenal protein) in the adrenal of the growth-restricted fetal sheep was significantly reduced, when compared with the expression of StAR protein (17.1 ± 1.9 AU/μg adrenal protein) in adrenals from the age-matched control group. In summary, there is a developmental increase in the expression of StAR mRNA and protein in the fetal sheep adrenal during the prepartum period when adrenal growth and steroidogenesis is dependent on ACTH stimulation. We have found that, while the level of expression of StAR protein is decreased in the adrenal gland of the growth-restricted fetus during late gestation, this does not impair adrenal steroidogenesis. Our data also suggest that the stimulation of adrenal growth and steroidogenesis in the growth-restricted fetus may not be ACTH dependent.

Differential Actions of Metyrapone on the Fetal Pituitary-Adrenal Axis in the Sheep Fetus in Late Gestation

Abstract It is not clear if an increase in intra-adrenal cortisol is required to mediate the actions of adrenocorticotropic hormone (ACTH) on adrenal growth and steroidogenesis during the prepartum stimulation of the fetal pituitary-adrenal axis. We infused metyrapone, a competitive inhibitor of cortisol biosynthesis, into fetal sheep between 125 and 140 days of gestation (term = 147 ± 3 days) and measured fetal plasma cortisol, 11-desoxycortisol, and ACTH; pituitary pro-opiomelanocortin mRNA and adrenal expression of ACTH receptor (melanocortin type 2 receptor), steroidogenic acute regulatory protein (StAR), 11β-hydroxysteroid dehydrogenase type 2 (11βHSD2), cytochrome P450 cholesterol side-chain cleavage (CYP11A1), cytochrome P450 17-hydroxylase (CYP17), 3β-hydroxysteroid dehydrogenase, and cytochrome P450 21-hydroxylase mRNA; and StAR protein in the fetal adrenal gland. Plasma ACTH and 11-desoxycortisol concentrations were higher (P < 0.05), whereas plasma cortisol concentrations were not significantly different in metyrapone- compared with vehicle-infused fetuses. The ratio of plasma cortisol to ACTH concentrations was higher (P < 0.0001) between 136 and 140 days than between 120 and 135 days of gestation in both metyrapone- and vehicle-infused fetuses. The combined adrenal weight and adrenocortical thickness were greater (P < 0.001), and cell density was lower (P < 0.01), in the zona fasciculata of adrenals from the metyrapone-infused group. Adrenal StAR mRNA expression was lower (P < 0.05), whereas the levels of mature StAR protein (30 kDa) were higher (P < 0.05), in the metyrapone-infused fetuses. In addition, adrenal mRNA expression of 11βHSD2, CYP11A1, and CYP17 were higher (P < 0.05) in the metyrapone-infused fetuses. Thus, metyrapone administration may represent a unique model that allows the investigation of dissociation of the relative actions of ACTH and cortisol on fetal adrenal steroidogenesis and growth during late gestation.

A premature increase in circulating cortisol suppresses expression of 11β hydroxysteroid dehydrogenase type 2 messenger ribonucleic acid in the adrenal of the fetal sheep.

Abstract We have investigated the effect of intrafetal cortisol administration, before the normal prepartum cortisol surge, on the expression of 11β hydroxysteroid dehydrogenase (11βHSD) type 2 mRNA in the fetal adrenal. We also determined whether increased fetal cortisol concentrations can stimulate growth of the fetal adrenal gland or increase expression of adrenal steroidogenic enzymes. Cortisol (hydrocortisone succinate: 2.0–3.0 mg in 4.4 ml/24 h) was infused into fetal sheep between 109 and 116 days of gestation (cortisol infused; n = 12), and saline was administered to control fetuses (saline infused; n = 13) at the same age. There was no effect of cortisol infusion on the fetal adrenal:body weight ratio (cortisol: 101.7 ± 5.3 mg/kg; saline: 108.2 ± 4.3 mg/kg). The ratio of adrenal 11βHSD-2 mRNA to 18S rRNA expression was significantly lower, however, in the cortisol-infused group (0.75 ± 0.02) compared with the group receiving saline (1.65 ± 0.14). There was no significant effect of intrafetal cortisol on the relative abundance of adrenal CYP11A1, CYP17, CYP21A1, and 3βHSD mRNA. A premature elevation in fetal cortisol therefore resulted in a suppression of adrenal 11βHSD-2. Increased intra-adrenal exposure to cortisol at this stage of gestation is, however, not sufficient to promote adrenal growth or steroidogenic enzyme gene expression.

N-Proopiomelanocortin (1–77) Suppresses Expression of Steroidogenic Acute Regulatory Protein (Star) mRNA in the Adrenal Gland of the Fetal Sheep

In the sheep, there is a rapid increase in fetal adrenal growth and steroidogenesis during the last 10–15 days gestation. Recently, we have shown that infusion of POMC (1–77) increases fetal adrenal growth and expression of CYP17 mRNA but does not significantly alter fetal plasma cortisol concentrations [1]. We therefore investigated the effects of infusion of bovine POMC (1–77) and its biosynthetic derivative POMC (1–49) on adrenal StAR mRNA expression. At 136d gestation, POMC (1–77) (n=5 fetuses; 2μg/ml/h), POMC (1–49) (n=5 fetuses, 2μg/ml/h) or Saline (n=5 fetuses, 1 ml/h) was infused for 48h. At 138d, fetal adrenal glands were collected and frozen in liquid N2 until RNA was extracted. Northern blot analyses demonstrated a major transcript for StAR mRNA at 3.0kb in fetal adrenal glands from all treatments. The membrane was stripped and re-probed with a 32P-labelled rat 18S rRNA oligo-probe to verify equal RNA loading. Infusion of POMC (1–77), but not POMC (1–49), resulted in a suppression of fetal adrenal StAR mRNA:18S rRNA when compared to adrenal StAR mRNA:18S rRNA from saline-infused controls. Our data suggest POMC (1–77) may act via separate mechanisms to increase fetal adrenal growth and to limit adrenal steroidogenesis through suppression of StAR mRNA.

Cortisol infusion decreases renin, but not PGHS-2, EP2, or EP4 mRNA expression in the kidney of the fetal sheep at days 109-116.

Renal prostaglandins (PG), renin, and cortisol are necessary for normal kidney development and function during fetal life. We examined the effects of cortisol infusion before completion of nephrogenesis (d 109–116 gestation; 2.0–3.0 mg hydrocortisone succinate/24 h) on the renal mRNA expression of PGHS-2, the PGE2 receptors, EP2 and EP4, and renin in fetal sheep. Cortisol infusion raised plasma cortisol levels to 42.8 ± 6.0 nmol/L compared with saline infusion levels of 1.5 ± 0.5 nmol/L (p < 0.001), but had no effect on fetal body weight, proportional kidney mass, or blood gases. Cortisol decreased significantly the relative expression of renin mRNA (saline: 0.93 ± 0.06 units; cortisol: 0.32 ± 0.03 units, p < 0.05), however it had no effect upon the expression of PGHS-2, EP2, or EP4 mRNA in fetal sheep kidney. Although there is substantial evidence that PGE2 acting through either the EP2 or EP4 receptor stimulates renin synthesis in the adult kidney, our results have demonstrated that before the completion of nephrogenesis, cortisol down-regulation of renin mRNA expression is independent of any change in the expression of PGHS-2, EP2, or EP4 mRNA expression. During nephrogenesis, the insensitivity of PGHS-2, EP2, and EP4 expression to down-regulation by cortisol may permit continued PG regulation of renal development and urine formation.

Role of Hypothalamic-Pituitary Axis in EGF Action on Maturation of Adrenal Gland in Fetal Rhesus Monkey In Vivo

We determined the route of action of epidermal growth factor (EGF) [intraperitoneal (IP) versus intraamniotic administration] on adrenal development and whether its effects are mediated via the fetal hypothalamic-pituitary axis in the fetal rhesus monkey in vivo. EGF (40 μg) was administered IP (n = 9) or intraamniotic (n = 6) at 121, 123, 125, and 127 d gestation (term, approximately 165 ± 10 d gestation). In addition, a competitive corticotropin-releasing factor antagonist ([d-phenylalanine12, Norleucine21,38] corticotropin-releasing factor12–41 to block fetal pituitary ACTH secretion; 400 μg IP) and metyrapone (11β-hydroxylase inhibitor to block adrenal cortisol synthesis; 15 mg IP and 15 mg intraamniotic) were administered, in combination with EGF (EGF+BLOCK; 40 μg IP;n = 4 fetuses). Control fetuses (n = 6) received saline injections in an equivalent volume. On gestational d 128, a hysterotomy was performed, and fetal adrenals were collected for morphometric analyses and immunocytochemical localization of 3β -hydroxysteroid dehydrogenase (3βHSD) and cytochrome P-450 11β -hydroxylase/aldosynthase. Definitive zone (DZ) width and cortical width of 3βHSD staining were significantly greater (p < 0.05) in the EGF IP-treated fetuses compared with controls and EGF+BLOCK. With EGF IP, 3βHSD was increased in the DZ and induced extensively in the transitional zone of the fetal adrenal cortex, and cytochrome P-450 11β-hydroxylase/aldosynthase immunoreactivity was induced to detectable levels in the DZ. The administration of EGF+BLOCK inhibited the expression of 3βHSD in the transitional zone, but 3βHSD expression was still increased in the DZ and cytochrome P-450 11β-hydroxylase/aldosynthase immunoreactivity was induced in the DZ. EGF intraamniotic administration had no significant effect on the width of the DZ or cortical width of 3βHSD staining compared with controls. These data suggest that EGF acts via the hypothalamic-pituitary axis to modulate adrenal cortical growth and functional maturation of the transitional zone (the putative zona fasciculata), whereas EGF can act independently of the hypothalamic-pituitary axis to stimulate functional maturation of the DZ (the putative zona glomerulosa).