Endocrinology---- Physiological Induction And completion of of Parturition Prof.Mahesh Chandra Bansal. MBBS, MS . MICOG. FICOG. Founder Principal & Controller; Jhalawar Medical College And Hospital, Jhalawar. Ex. Principal & Controller; Mahatma Gandhi Medical College And Hospital, Sitapura , Jaipur.
1. Prof.Mahesh Chandra Bansal. MBBS, MS . MICOG. FICOG. Founder
Principal & Controller; Jhalawar Medical College And Hospital,
Jhalawar. Ex. Principal & Controller; Mahatma Gandhi Medical
College And Hospital, Sitapura , Jaipur.
2. Introduction How and what Makes the labour process to switch
on ?It remains poorly defined till date. Two major components are
thought to be concerned with labour initiation--1. Loss of
functions pregnancy maintenance factors . 2. Synthesis of factors
that induce parturition. Phase 1 of parturition starts well before
the actual labour starts.
3. Mechanism Of Myometrial Quiescence In Pregnancy
4. Factors responsible for maintenance of pregnancy 1.
Myometrial quiescenceis likely to be the result of many factors
that include--a. Estrogen and progesterone action through intra
cellular receptors. b. Myometrial plasma membrane receptor
---mediated increase in cAMP. c. Generation of cGMP. d. other
systems including modification in myometrial cell ion channels.
Uterine quiescence is so remarkable that all manners of
biomolecular systems Neural.Endocine, Paracrine and Autocrine are
operating are operating to implement and maintain a state of
uterine un responsiveness to all factors which can stimulate
myometrial contractions.
5. Role of Sex Steroids in Uterine Quiescence while estrogen
promotes myometrial Progesterone inhibits contractility. Low
progesterone level in LPD case ---Abortion Can be prevented by Rx
with progesterone . Progesterone therapy causes--- Physiological
encirclage in cases of incompetent Os. Progesterone antagonists
Mifepriston ( Ru486 and Onapriston can induce abortion and
premature labour. Progesterone i9nduces uterine quiescence directly
/ indirectly ---causing decreased expression of myometrial
contraction proteins (CAPS ). Progesterone inhibits expression of
Gap Junction proteins connexon 43 --- Use of progesterone
antagonist (Ru 486 ) leads to premature induction of this Connexon
43 protein production there by initiate of labour. Fall in
Progesterone and relatively high level of Estrogens at term has
been co related with onset of parturition phase 2.
6. Role of Receptors in Myometrial Quiescence G- protein
receptors B Adreno receptors---stimulantsRetodine /terbutalin ,
sabutamol Isoxipurine are used to control premature labour LH &
hCG receptors--- hCG therapy is used to control pregnancy loss in
LPD, ART cases These all receptors in coordinated way bring uterine
relaxation--- No of G-protein receptors associated with G- alphas
mediated activation of adenolyl cyclase cAMP together with
appropriate legands act in concert with progesterone -- as part of
fail safe system to maintain myometrial quiescence.
7. Role of Relaxin In Uterine Quiescence Relaxin a peptide
hormone having A & B chains more similar to insulin family
proteins. Relaxin--- there are 2 separate human relaxin genes H1
And H2. H1 is expressed in decidua, trophoblasts where as H2 is
primarily expressed in carpus luteum . During pregnancy relaxin is
mostly produced by carpus luteum . Plasma membrane surface
receptors for relaxin ---Relaxin family peptide receptors 1( RXFP1)
---mediates its activity by activation of adenolyl cyclase ----
results in relaxation of all smooth muscles , ligaments of joints
and myometrium during pregnancy. Relaxin also effects cervical
modulating through cell proliferation and changes in extracellular
cell matrix of cervix ---cervical softening , ripening and dilation
in phase 1 of parturition.
8. Role of Cortico Tropin Releasing (CRH)Hormone on Myometrium
CRH-- is produced by Hypothalamous and placenta. Recent studies
reveal that CRH plays dual role onmyometrium during pregnancy and
parturition. These actions are mediated through specific CRH
receptors variants present 0n myometrium . During pregnancy it
signals pathways, initiate cAMP and subsequent relaxation. CRH
hormone increases in last 2 weeks of pregnancy and activates
Gq-alpha protein pathway ---- favors myometrial contraction.
9. Prostaglandins --- myometrial relaxant Prostaglandins
interact with a family of eight different G protein coupled
receptors. Several of them are present on myometyrium. Tp trombxane
1 A2 ,DP-PGD2, IP prostacyclin or PGI2, FP-PGF2 a ,and EP1,2,3and 4
, PGE2 receptors etc .Prostgladin PGI2 could potentiate myometrial
relaxation by increasing camp signaling. Many studies show that
there are many regional changes in upper and lower segment during
pregnancy. An variable concentration gradient of different PG
receptor from fundus towards cervix has been noted. Thus it is
entirely possible that prostanoids contribute to uterine quiescence
in pregnancy and myometrial contraction at the time of
parturition
10. Natriuretic Peptide And Cyclic Guanosine
monophosphate(cGMP) --Uterine Quiescence Activation of guanylyl
cyclase increases intracellular concentration of cGMP in myometrium
and results in its relaxation. Intra myometrial cGMP is also
increased by Atrial and Brain Natriuretic peptides (ANP & BNP
)--- both are present in myometrium during pregnancy. BNP is
secreted by amnion in large amount while ANP is expressed by
placenta. Soluble Guanylyl Cyclase is also activated by Nitric
Oxide which penetrates the plasma membrane of myometrium --- Nitric
oxide reacts with Iron and stimulates Guanylyl Cyclase to produce
plenty of cGMP and myometrial relaxation . How much role does this
mechanism play in uterine quiescence is not much clear?
11. Accelerated Uterotonins Degradation---Uterine quiescence
There is strikingly increased activities of enzymes --that degrade
or in activate the uterotonins --- Bio-Chemicals that stimulate
uterine contractions. PGDH degrades PGs. enkephalinase and
endothelins. Oxytocinase--- inactivate oxytocin. Diamine oxidase
and Histamine. Catachol-o methyl transferase. Angoitensinase and
Angiotensin II. Platelet activating Factor( PAF ), acetyl hydralase
and PAF etc. Activity of these degrading and inactivating enzymes
is increased by progesterone.
12. Summary of factors ---Cause Uterine Quiescence Receptors
--- G. Proteins ,B adenolyl cyclase cAMP and legends ,LH & hCG
and Progesterone receptorsRelaxin Cortico tropin Realeasing
HormoneUterine QuiscenceProgesteroneNitric Oxide Prostacylins
Apocrines & autocrinesANP, BNP and cGMP Degradation of
Uterotonins
13. Machanism Of Uterine contractions In Parturition
14. Possible mechanism of Initiation of labour Fetus is initial
source of signals for parturitioninitiation . One or many
uterotonins( Bio chemicals thatstimulate myometrial contraction )
produced in increasing amount and presence of myometrial receptors
on/ in myocytes for uterotonins.
15. Unique features of myometrium Degree of muscle fiber
shortening with contraction isgreater than that of skeletal muscle
fiber. Force generated by myometrial muscle contraction can be
extended in multiple directions . In myometrium , the thick and
thin filaments are filaments are found in long and Random bundles
throughout the muscle cell . This plaxiform arrangement aids
greater shortening and force generating capacity to the muscle
cell. Greater multidirectional force generation occur in the
uterine upper segment as compared to lower segment which permits
versatility in expulsive force directionally.
16. Regulation of myometrial Contraction And Relaxation
Myometrial Contraction ---controlled by transcriptionof Key Genes ;
that produce kinetic proteins that repress/ enhance cellular
activity. These Kinetic proteins 1. Enhance the inter action
between Actin & myosin proteins bring about muscle contraction
2. increase excitability of each individual cell. 3.Promote
intracellular cross talk that allows synchronous contraction.
17. Actin Myosin Interaction Actin-Myocin interaction is
essential for muscle contraction. Interaction needs conversion of
globular Actin in to filamentous form . Actin must be attached to
at a focal point at cytoskeleton in the cell membranes to allow
tension. Actin must partner with Myosin. Myosin Is composed of
light and heavy chains . Interaction of Actin Myosin Needs
activation of ATP --- ATP hydrolysisGeneration of energy e.g.
Force. This is brought about by Enzyme Phosphorilationof the 20KDa
(light chain of Myosin. Phosphorilation reaction is catalyzed by
Both the enzyme Myosin light chain Kinase activated By Ca++. Ca++
binds to Calmodium , a Ca ++ binding regulatory protein, --This
complex binds and activate the Myosin light chain Kinase. As
explained in FiG A and B
18. Role of Ca++ in Myometrial Contractility Myometrial
contractility is regulated by electro chemical potential gradient
across the cell membrane. Prior to labour Myocyte maintains
High(Intra cellular ) electro negativity . This state is maintained
by combined actions of ATPase driven Na+ --- K + Pump and large
conductance ; voltage andCa2++ sensitive K channel called maxi K
Channel. During uterine quiescence . This maxi-K channel is opened
and allows K+ to move out of cell and thus the intra cellular
electro negativity is maintained. At the time of labour electro
negativity leads to depolarization and brings about contraction .
Myocyte contraction requires intracellular influx of Ca2++ through
legend and voltage regulatory channels. Ca2++ influx is brought
about by agents like PgF2a and oxytocin . PGF2a and oxytocin
combines with their receptors and open the legend activated Ca2++
channels. Activation of these receptors also release Ca++ from
internal sacroplasm reticulum . Increase intracellular Ca== leads
to drop in intra cellular electro negativity --action potential is
generated ----Actin Myosin interaction ------myocyte
contraction
19. Gap Junctions in /Myometrium cellular signals for
contraction relaxation are transferred Gap junctions are
intercellular channels through which , from one myocyte to
adjoining myocyte. Establishment of intercellular communication
also aids in the process of electric, ion and metabolic coupling .
Transmembrane channels that makeup the gap junctions-- consists of
2 proteins ; called hemi channels also termed as Connexons. Each
connexon is made of 6 sub unit proteins These pair of connexons
establish conduit between couple cells for the exchange of small
molecules like nutrients b, waste products, metabolites . Ions and
second massagers etc.
20. Myometrial Cell surface receptors There are many surface
receptors which directly regulate the myocyte contraction state.
Their major Varieties are 1. G. protein linked 2. Ion channel
linked and 3.Enzyme linked. G. Protein linked receptors associated
with Adenolyl cyclase activation example LH and CRHR1a receptors
,G.protein mediated activation of Phosphoryilase C. Legend of G.
coupled receptors also include neuropeptides, hormones and
autocoids . These varieties of cell surface receptors are increased
many fold in pregnancy and parturition . Their modes include
endocrine, paracrine and autocrines and through the surface
receptors they effect / modulate the myomtrial response during
pregnancy and parturition.
21. Autocrine
22. Role of Functional Progesterone Withdrawal in human
Parturition There are varieties of progesterone receptors(A)
Nuclearprogesterone receptor protein isomersPRA,PR-Band PR-C .and
their co activtors . (B) Membrane associated progesterone receptors
mPRalpha, mPR-beta, mPR-y.mPR alpha and beta couple with inhibitory
G. proteins , legend binding to these receptors decreases cAMP
levels and increase myosin phospholyration both of them increase
myometrial contractility at term . Multiple pathways exist for a
functional withdrawal of progesterone in term myometrium to make it
less quiescent and more responsive to contraction effect of
utertonins
23. Estrogens ---myometrial preparation for Parturition
Estrogen level remain high throughout the pregnancy ,but functional
withdrawal of progesterone ---makes its upper hand. Estrogen Brings
about myometrial hyperplasia and hypertrophy during early
gestational period . It promotes glycogen storage in myometium . It
enriches Myometrial with ATP, Ca++. It makes myometrium more
sensitive to uterotonins like Oxytocin, PGE2 and PGF2a.
24. Oxytocin Receptors---Phase 2 Of Parturition There is marked
increase in number of oxytocin receptors and their activation in
phase2 of parturition; more over there activation in increased
Phospholipase C activity, subsequent influx of Ca++ in cytoplasm of
myocytes and increased uterine contractility. The level of oxytocin
receptor in human term myometrium is greater than that in preterm
myometrium . Estradiol and progestins are primary regulators of
oxytocin receptors expression . Estradiol increase oxytocin
receptors which can be prevented to some extend by progesterone
therapy. Progesterone increase degradation of intra cytoplasmic
oxytocin receptors and inhibit the activation of oxytocin receptors
on cell surface too.
25. Relaxin in Phase2 OF Parturition Relaxin Though plays its
role in uterine quiescence inpregnancy, but also has its role in
remodeling the Extra cellular tissue of female genital tract ,Pubis
symphysis and breast. Relaxin mediate synthesis of Glycoso
aminoglycans , prtoglycans and matrix metalloproteases which
degrade macro molecules of collagen.
26. Fetal Placental Cascade leading to Parturition Activation
of Fetal Hypothalmo-pituitary- Adrenal axis at term--- ACTH
secretion. Fetal Adrenals --- produce DHEA-5. cortisol and
Estradiol by aromatization . Fetal Adrenals are also stimulated by
placental CRH. CRH levels are increased in maternal , fetal
circulation as well as in amniotic fluid . Fetal cortisol also
stimulates fetal CRH which modulate uterine contractility through
CRH-Rid isomers of CRH receptors . Fetal cortisol---increases
myometrial contractility by stimulating Prostaglandin biosynthesis
by fetal membranes, Fetal adrenal estrogen crosses placental
barrier and reach in maternal circulation ---changing estrogen to
progesterone ratio---promote series of contractile proteins in
myometrium ---loss of uterine quiescence. Increased CRH level in
last weeks of gestation and phase2 of parturition reflects A FETAL
PLACENTAL CLOCK.. Thus fetus and placenta through their
endocrinological events influence the timing of parturition
27. CRH) in phase 2& 3 of parturition In late pregnancy and
parturition the modification inCRH receptors expression --- favors
its role cAMP (relaxation effect ) to protein Kinase C activation
--results in increased Ca++ influx in myometrium --myometrial
contractions start. Oxytocin attenuates CRH receptors expressing
through cAMP and so the CRH now augments the contractile
responsiveness of myometrium to even small dose of oxytocin at
term. CRH also acts to increase the myometrial contraction force in
response to PGF2a.
28. Fetal Lung Maturity And parturition Surfactant proteins A (
SP-A )produced by fetal lung isrequired for fetal lung maturity.
Pulmo-bronchial tree is communicating with amniotic sac SP-A level
rises in amniotic fluid , parallel to lung maturity--- It activates
fluid macrophases ---migrate to endometrium and induce Nuclear
Factor-KB. Nuclear factor KB activates inflammatory response genes
in myometrium --- promote PG receptors and PG synthesis too ---
increased myometrial contractility. Pulmonary surfactant and other
surfactant components such as platelet activating Factor when
secreted in Amniotic Fluid ---- have been reported to induce PGs
synthesis and uterine contractions.
29. Utertonins---Systems to ensure Success of Phase 3 ofLabor
initiation by Current data favor the theory of parturition
uterotonins. Increased production of uterotonins must follow once
phase one is suspended, phase 2 is implemented . Number of
uterotonins are important for success of phase 3 e.g. Active labor.
Uterotonins are--- Oxytocin, prostaglandins, serotonin ,histamine,
PAF, Endothelin , Angiotensin II and others--- all have been shown
to stimulate myometrial contraction through G protein
coupling.
30. Oxytocin = Quick Birth,(Synthesis) Magnacellular Neurones
of Supra optic , Paraventricular nucleus Of HypothalamusProduction
of ProhormoneTransported with Carrier Protein Neuro physinNeural
lobe of Posterior Pituitary Stored in VesiclesProhormone is changed
by Enzyme in to Oxytocin during Transport
31. Oxytocin In phase 2,3 and 4 of parturition Number of
Oxytocin receptors in myometrium and other tissues are increased by
> 50 fold at term. Oxytocin acts on decidua to produce PGs.
Oxytocin is also produced locally by decdiua, Extra embryonic fetal
tissue and placenta. The blood level of active Oxytocin is increase
many times during active phase of labor and immediately after the
end of 3rd stage . Its secretion also increases during Breast
feeding. Oxytocin produces increased level of mRNA in myometrial
genes that encode proteins ----interstitial collagenase , monocyte
attractant , interleukin 8 and urokinase plasminogen activator
---those help in uterine contraction and retraction --- more so in
puerperium necessary for involution.
32. Prostaglandins in Phase 3 of Parturition Phase 2 is limited
and unclear , but these play Role of PGs ina critical role in phase
3 of parturitionEvidenced by- 1. Levels of PGs and metabolites
increase in myometrium, AF, decidua, maternal plasma and urine in
active labor. 2. Administration of PGs can result in abortion /
delivery at any gestational period. 3. Administration of PGHS-2
inhibitors like Endomethacin/ Aspirin can inhibit myometrial
contractions. 4. Receptor for PGf2a increase in decidua and
myometrium at term a most regulatory step in action of PG on
myometrium. 5. Myometrium itself also synthesizes PGHS-2, though
decidua is main source of PGs. 6. PGs level increases in fore water
bag more than that in hind water bag due to local damage to
separating decidua. Pgs along with cytokinins result in degradation
of cervical matrix --- cervical ripening and dilatation
33. Platelet Activating factor(PAF) PAF is produced In
Basophill.Eosinophills, Neutophills,monocyes, macrophase and
endothelial cells.PAF receptors are member of G. protein coupled
family of trans membrane receptors. PAF is inactivated by PAF
acetylhydrolase(PAF-AH) present in macrophases found in large
amount in decidua during pregnancy and inhibits PAF action On
Myometrial cell membrane--- no Ca++ influx in myocytes during
pregnancy and help in uterine quiescence. But at term and during
labor level of PAF increases locally and its inhibitory effect is
absent(no enzymaic inhibition ) as a result PAF activity Increases
Ca++ influx in myometrium and uterine contraction start.
34. Endothelin -1 Endothelins are a family of 21 amino acid
peptides. Its receptor endothelin A receptor is present on
musclecells and is stimulated by endothelin 1 to increase Ca++
influx in muscle cell resulting in myometrial contraction.
Endothelin1 is present in myometrium and amniotic fluid during
labor . Enzyme to catalyze and inhibit its action is also present
in chorion leave during pregnancy Uterine quiescence --- It
decreases at term.
35. Angiotensin II in phase of parturition There are 2 types of
G. protein linked AngiotensinReceptors AT 1 & AT2. AT2 is
prominent in non pregnant uterus , AT 1 is expressed during
pregnancy and labour . Potential mechanism of Angiotensin II
through receptor AT1(by increased responsiveness ) during PET and
eclampsia emphasizes its role in physiology of Parturition.
36. Contribution of Intra uterine tissue To Parturition Intra
Uterine TissueThey have a potential role in parturition initiation
Amnion , chorion laeve and decidua parietals are likely to have
alternate action .Amnion and decidua comprises and important tissue
cell around fetus that serves as physical, immunological and
metabolic protective shield that protect against untimely
initiation of parturition. In late weeks of gestation the amniotic
membranes indeed may prepare for initiation of parturition.
37. Contribution of Intra uterine tissue To Parturition Amnion
Tensile strength of membranes and resistance torupture is provided
by amnion. -This avascular tissue is highly resistant to
penetration by leucocytes and micro organisms. - It also serves as
protective filter to prevent fetal particulates bound lung and skin
secretion of fetus from entering in maternal circulation i.e.
adverse effect of fetal particulates and secretion on deciduas,
myometrial activation and even Amniotic fluid embolism. - several
bioactive peptides and PGs are secreted ( synthesized Phospholirase
A2 and PGHS2 )by amnion and these regulate the events to initiate
the process of parturition and rupture of membranes.
38. Amnion --- Cont. Influence of amnion derived PGs on uterine
quiescenceduring pregnancy and uterine contractions during labor is
less clear. Decidua prevents their( PGs) penetration to myometrium
and inactivation by PG Dehydrogenase enzyme --- keep them away from
myometrium during pregnancy ---uterine quiescence is maintained. In
late weeks of pregnancy production and activity of PG dehydrogenase
decreases markedly and at the same time decidual permeability to
amnion PGs also increases , increased synthesis of PGs by
increasing activity of phospholirase A2 and PGH synthase type 2
(PGSH 2) enzymes . Thus expression of PGf2 a on myometrium through
increased PG receptors in myometrium --- it plays an important role
in initiation of labor.
39. Decidua Parietalis Generation of decidual
uterotonins---that act in paracrine manner on myometium. Decidua
expresses steroidal metabolic enzymes such as 20aHSD and 5a R1
---they regulate local progesterone withdrawal. Deciduas prevents
penetration of amniotic PGs to myometrium and PGs dehydrogenase
enzyme activity destroys PGS. --- Uterine quiescence during
pregnancy. Decidual contribution to active labour in late pregnancy
appears to be localized to the exposed decidual fragments lining
the forewater bag which has separated from its attachment with
myometrium of lower segment. Trauma ,hypoxia , exposure of fore
water bag decidual fragments to endotoxins--- lipopolysccides,
micro organisms, interleukin1B(IL-1B)present in the vaginal fluids
---provoke inflammatory process as cervical canal is partially open
.
40. separated fore water bag from cervical tissueFragmented
Decidua inflammatory reaction by elements in vaginal fluid
41. Partially Dilated cervix and more exposed fore water bag to
vaginal fluid
42. This inflammatory action ---cytokinines are produced
Decidua parietalis---- membranes ----increase production of PGs in
amnioticcan reach to myometrium and act directly on
it-----initiation of uterine contraction. Tumor Necrotizing Factor
alpha (TNFa) and interleukins 1, 6, 8, and 12 also act as
chemokinines that recruit to the myometrium Infiltration of
leukocytes--- as inflammatory process --production of cyokinines
and increased phospholyration of Archadonic acid to
PGF2a.----increased uterine activity . Major role of decidual PGs
regulation is not only increased permeability to PGs ,but its
production also and increased expression of PGF2a receptors on
myometrium.
43. Progesterone withdrawalDecidual fragmentation, inflammatory
actionincreased Estrogen - increasedE2 receptors & their
response.Producton of Oxytocin, PGF2aInitiation Of
Parturition-G-proteins coupled receptors-actin myosin action phase
2,3,4,Altered E:P ratiodecreased activity of Oxytocinase
activityFerguson reflex cervical compliance ripening dilatation
,Streachibilit y Pgs synthesisPgs synthesis in fetal membranes
PGF2a &PGE2 promote Gap Junction , increase d response to
receptors E2, oxytocin ,cytokinines,PAF, endothelines , PGs
synthesis ---increased Uterine contractilityFetal Adrenals
Pituitary axis --cortisol,estradiol e production from DHt from
placenta
44. Summary( phase 3,4 of parturition) It is possible that
multiple and redundant processescontribute to success of active
labour as once the phase 1 ( uterine quiescence and cervical
remodeling) ends, and phase 2 is implemented. Phase 3 is
highlighted by activity of G proteins coupled receptors which
inhibit cAMP formation , increases intracellular Ca++ storage
action potential generated , ATP liberate energy , acting myosin
action --- bring myometral contractions. Increased , coordinated
progressive and effective myometrial contractions with sufficient
amplitude and frequency generate enough force ---pressure gradient
and increased intra uterine pressure needed to push fetus downwards
in birth canal.
45. Summary--- Simultaneously cervical protoglycans bring about
changes in collagen tissue of cervix --- promote structural
changes, cervical tissue compliance, increased softness,
strachibility, distensionablity,---progressive cervical dilatation
. The source of regulatory legends --- receptors variation ,
endocrinological hormones such as oxytocin to locally produce PGs
in fetal Membranes . In phase 4 , a complete series of repair
forces and initiative to resolve inflammatory response ---removal
of glycosoaminoglycans, protoglycans and structurally compromised
collagen . Simultaneously intercellular matrix and cellular
components needed for uterine involution are synthesized. Dense
connective tissue and structural integrity of rigid, firm, closed
cervix --- cervical reform--- also achieved . Other body parts are
also march back to their pre pregnancy status--- so far
possible.