Vasointestinal peptide Oxytocin
Calcitonin gene-related Follistatin
In other words, both maternal and fetal physiology during pregnancy are in´¬‚u-
enced by placental secretion of neurohormones and other regulatory molecules
(Figure 1.1). Human placenta decisively contributes to all phases of gestation, and
placental neurohormones are critical in providing a favorable uterine environ-
ment. When maternal or fetal acute or chronic hostile events occur, placental
secretions may protect the feto-placental unit, and/or trigger parturition, thus
helping the fetus to escape from a hostile environment.
The present chapter will review the experimental and clinical studies on the pos-
sible role of placental neurohormones and related molecules in physiological and
pathological conditions occurring throughout gestation.
18 F. Petraglia et al.
and amino Fetal growth
Invasion of contractility and behavior
Figure 1.1 The putative role of human placenta throughout pregnancy. The secretion of neurohormones,
neuropeptides and neurosteroids is able to affect several maternal and fetal functions
through endocrine mechanisms, but at the same time is also able to affect several
placental functions in autocrine/paracrine ways
Neurosteroids and monoamines
Neurosteroid is a generic denomination applied to the steroid hormones which are
synthesized within the nervous system, either de novo from cholesterol, or by the
metabolism of precursors obtained from an outside source. The placenta is a source
of several neurosteroids comprising progesterone itself, its derivates 5 -pregnan-
3a-ol-20-one (allopregnanolone) and 5 -dihydroprogesterone (5 -DHP), and
its precursor pregnenolone sulfate (Dombroski et al., 1997; Le Goascogne et al.,
2000). The levels of allopregnanolone in maternal serum increase progressively
during gestation and, diversely from progesterone, are augmented in hypertensive
complications of pregnancy (Luisi et al., 2000). Apart from progesterone, the role
of placental neurosteroids in the physiology of pregnancy is largely unknown.
These hormones may contribute to the neurochemical and behavioral changes of
pregnancy and puerperium, since they interfere with gabaergic circuits and have
19 Placental expression of neurohormones and other neuroactive molecules
anxyolitic effects (Dombroski et al., 1997). Placental neurosteroids may also con-
tribute to myometrial quiescence, as suggested by their ability to reduce the con-
traction frequency of human myometrial strips in vitro (Lofgren et al., 1992).
The placenta is a source and target for epinephrine, norepinephrine, dopamine and
5-hydroxitryptamin (serotonin). The enzymes involved in monoamine synthesis
and metabolism as well as monoamine transporters and receptors have been iden-
ti´¬üed in the placenta (Falkay and Kovacs, 1994; Bzoskie et al., 1997; Vaillancourt
et al., 1998; Kenney et al., 1999; Nguyen et al., 1999). Several studies have suggested
that local monoamines participate in the regulation of placental function. The pla-
cental metabolism and transport of these neurohormones has an important role in
determining the availability and bioactivity of biogenic amines to both mother and
fetus. In preeclampsia (PE) there is an increased activity of tyrosine hydroxylase
in placental tissue and this is likely to contribute to the higher levels of cate-
cholamines in maternal circulation (Manyonda et al., 1998). It has been shown
that placental norepinephrine transporter mRNA expression is reduced in some
gestational diseases, resulting in increased norepinephrine levels in fetal circula-
tion (Bzoskie et al., 1997). The activity of serotonin transporter in placental cells is
suppressed by agonistic stimulation of cannabinoid receptors, indicating that pla-
cental clearance of serotonin may account for adverse effects of cannabinoid use
during pregnancy (Kenney et al., 1999).
Peptide signaling and placental endocrinology
Human placenta plays a fundamental role in the physiology of pregnancy. Its most
relevant role is to maintain an equilibrium between the fetus and the mother, reg-
ulating the body functions of both organisms in a complementary way. Initiation,
maintenance and termination of pregnancy are related to placental functions.
Under this interpretation, the capacity of hormonal production in placental cells is
critical in providing a favorable uterine environment at implantation, in regulating
fetal growth during pregnancy and in directing the appropriate signals for the tim-
ing of parturition.
Increasing evidence indicates that maternal or fetal physiological and patholog-
ical stress conditions in´¬‚uence placental secretion of neurohormones, so that
endogenous or exogenous stress stimuli stimulate the placenta to take an active
role in responding to these adverse conditions.
A major role for the various peptides produced by the placenta, fetal membranes
and decidua is the control of local placental hormonogenesis. The various neuro-
hormones act on local hormone secretion through paracrine and/or autocrine
mechanisms, as their actions may occur in the same tissue where they originate as
well as in the contiguous tissues.
20 F. Petraglia et al.
CRH, CRH-BP and urocortin
Immunoreactive corticotropin-releasing hormone (CRH; Box 1.1) was ´¬ürst
detected in extracts of human placenta obtained at full term from spontaneous
delivery (Shibasaki et al., 1982) and was found to be as bioactive as rat hypothala-
mic CRH or synthetic ovine CRH on the release of immunoreactive adrenocorti-
cotrophic hormone (ACTH) and -endorphin ( -END) from cultures of rat
Box 1.1 Corticotropin-releasing hormone
The CRH is a 41 amino acid peptide released from the medial eminence of the
hypothalamus, acting at the corticotroph cells in the anterior pituitary to stim-
ulate the release of ACTH and related peptides in response to stress events, and
modulating behavioral, vascular and immune response to stress (Vale et al.,
1993). Human placenta, decidua, chorion and amnion also produce CRH
(Petraglia et al., 1992a; Warren and Silverman, 1995).
Expression and localization
Placental villi at term immunostained for CRH show the presence of the neuro-
hormone in some cytotrophoblast cells (Saijonmaa et al., 1988), as well as in
syncytiotrophoblast cells (Warren and Silverman, 1995). Cytotrophoblast cells
are transformed to syncytial cells, which release CRH factor when maintained
in culture (Petraglia et al., 1987c; Frim et al., 1988; Jones et al., 1989; Riley and
Other than from placental cells, CRH is also released from cultured amnion,
chorion and decidual cells at term (Robinson et al., 1988; Jones et al., 1989; Riley
and Challis, 1991) with an output similar to that by the placental cells (Jones
et al., 1989). Immunohistochemical localization of CRH in fetal membranes
showed that CRH is distributed in the epithelial cells, in some cells of the subepi-
thelial layer of amnion, and in cells of the reticular layer of chorion (Saijonmaa
et al., 1988; Warren and Silverman, 1995). Immunoreactive CRH is present in
decidual cells (Petraglia et al., 1992a) as well as in endometrial cells treated hor-
monally to achieve in vitro decidualization (Ferrari et al., 1995).
The CRH (and urocortin) interact with two distinct receptors (Valdenaire et al.,
1997): R1 (classi´¬üed in R1a, R1b, R1c, and R1d subtypes) and R2 (R2a, R2b and
R2g subtypes) (Petraglia et al., 1990c; Leung and Peng, 1996). Fluorescent in situ
hybridization and immuno´¬‚uorescence demonstrated that syncytiotrophoblast
21 Placental expression of neurohormones and other neuroactive molecules
cells and amniotic epithelium are the cell types expressing CRH-R1a, -Rc
(Karteris et al., 1998) and -R2beta mRNA (Florio et al., 2000).
The CRH receptors (mRNA and protein) have also been described in human
myometrium (Grammatopoulos et al., 1998). In particular, recent ´¬ündings
show the presence in pregnant myometrium of subtypes 1a, 1b, 2a and 2b, and
the variant -Rc, whereas only the 1a, 1b and 2b receptors are detectable in non-
pregnant myometrium (Hillhouse and Grammatopoulos, 2002). Urocortin
binds to CRH receptors types 1 and 2, with a particularly high af´¬ünity for type
2 receptor (Vaughan et al., 1995).
Levels in biological ´¬‚uids
From intrauterine tissues, CRH is reversed into the maternal and umbilical cord
plasma, as well as the amniotic ´¬‚uid. Plasma CRH levels are low in non-pregnant
women ( 10 pg/ml) and become higher during the ´¬ürst trimester of pregnancy,
rising steadily until term (Petraglia et al., 1996d; Reis et al., 1999; Reis and Petraglia,
2001; Florio et al., 2002d). The CRH is also measurable in fetal circulation, and a
linear correlation exists between maternal and fetal plasma CRH levels, despite
umbilical cord plasma CRH levels are 20ÔÇ“30-fold lower than in maternal circula-
tion (Economides et al., 1987). In addition, CRH concentrations in umbilical
venous plasma are higher than in the umbilical artery, supporting placenta as a
major source of fetal plasma CRH (Goland et al., 1988). The signi´¬ücant correla-
tion between the amniotic ´¬‚uid and maternal plasma CRH levels obtained
simultaneously (Laatikainen et al., 1988) suggests a placental source for amni-
otic CRH: amniotic ´¬‚uid levels are similar to those circulating in cord plasma
(Reis et al., 1999).
anterior pituitary cells (Sasaki et al., 1988). The structure of placental CRH mRNA
is similar to that predicted for hypothalamic CRH mRNA (Florio et al., 2002d).
The content of immunoreactive CRH is higher in extracts of placenta obtained at
term than in tissue obtained at 10 weeks of gestation (Schulte and Healy, 1987;
Frim et al., 1988) and a progressive increase of placental CRH content increase has
been described during normal pregnancy, paralleling a similar time course of pla-
cental CRH mRNA expression, which starts from early gestation (7ÔÇ“8 weeks)
(Grino et al., 1987; Frim et al., 1988).
Some mechanisms stimulating CRH release from medial hypothalamic eminence
in the brain (Vale et al., 1993) are identical to those operating in the human pla-
centa (Figure 1.2). In fact, prostaglandins (PGs), neurotransmitters and peptides
stimulates the release of CRH from cultured placental cells. Both prostaglandin
F2 (PGF2) and E2 (PGE2) increases the CRH concentration in the culture medium
22 F. Petraglia et al.
Nepi, Ach, PGF2, PGE2, Nepi, Ach, PGF2, PGE2,
AII, AVP, OT, IL-1
IL-1, AII, AVP, OT
Figure 1.2 The mechanisms stimulating CRF release from medial basal hypothalamus are in part
chemically identical to those operating in the human placenta. PGF2 and PGE2,
norepinephrine (Nepi), acetylcholine (Ach), angiotensin II (AII), arginine vasopressin
(AVP), stimulate CRF in hypothalamus, as well as in placental cells. On the contrary, the
effect of OT on CRF and HPA hormones in human placenta, is different being stimulatory.
In turn, placental CRF stimulates ACTH secretion from cultured human placental cells
with a dose-dependent effect (Petraglia et al., 1987c). Norepinephrine and acetyl-
choline are the most active neurotransmitters in increasing CRH release.
In particular, the norepinephrine effect is reversed by prazosin, an 1-adrenergic
antagonist, or yohimbine, an 2-adrenergic receptor antagonist. The involvement
of both adrenergic receptor subtypes is further supported by the evidence that
methoxamine or clonidine, 1- and 2-adrenergic receptor agonists, respectively,
stimulate CRH release from placental cells (Petraglia et al., 1989c). Acetylcholine
acts via a muscarinic receptor: atropine or hexamethonium, speci´¬üc muscarinic
receptor antagonists, reverse the effect of acetylcholine on CRH release. In addi-
tion, the human placenta synthesizes acetylcholine and contains acetylcholine
concentrations higher than in mammalian brain tissue (Petraglia, 1991; Petraglia
et al., 1996d; Reis et al., 2001). Interestingly, the positive effect of norepinephrine
and acetylcholine on placental immunoreactive CRH release agrees with the obser-
vation that these neurotransmitters stimulate CRH release from rat hypothalamic
tissue in vitro and increase CRH levels in the hypophysial portal circulation
(Plotsky et al., 1989), suggesting a close correlation between hypothalamic and
placental regulation of CRH release (Figure 1.2).
In agreement with the hypothalamic mechanisms of secretion, some neuropep-
tides also modulate placental CRH release. Angiotensin II and arginine vasopressin
increase the release of placental CRH from cultured trophoblasts (Petraglia et al.,
1989c). On the contrary, oxytocin (OT) has different effects, being inhibitory to
23 Placental expression of neurohormones and other neuroactive molecules
CRH/hypothalamusÔÇ“pituitaryÔÇ“adrenal (HPA) axis (Plotsky et al., 1993), while stimula-
tory on CRH and ACTH secretion from cultured placental cells (Petraglia et al., 1987c).
The CRH and both groups of neurotransmitters (norepinephrine and acetyl-