Endocrinology --- control of parturition

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.

Endocrinology --- control of parturition

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myometrial progesterone

uterine quiescence relaxin

progesterone therapy

role of receptors

pregnancy relaxin

progesterone action

gprotein receptors

role of relaxin