Human Parturition and Birth: Regulation

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Figure 1.

Myometrial contraction. Increased MLCK activity results in contraction. This enzyme activity is increased by Ca2+ and decreased by cAMP and cGMP.

Figure 2.

Influence of the fetus on parturition.

Figure 3.

PG synthesis. Arachidonic acid is released from cellular phospholipids by phospholipases. It is transformed to a short‐lived intermediate PGH2 by prostaglandin H2‐synthase. PGH2 is then converted by specific synthases into PGE2, PGF or prostacyclin (PGI2).

Figure 4.

Regulation of prostaglandin formation in the uterus. PG, prostaglandin; PGHS‐2, prostaglandin H2 synthase type‐2; 15OHPGDH, PG dehydrogenase.

Figure 5.

Feed‐forward loop for increasing prostaglandin production in human uterus. PGs: prostaglandins; PGDH, PG dehydrogenase, PGHS‐2, PGH2 synthase type‐2; 11βHSD‐1, 11βhydroxysteroid dehydrogenase type‐1.

Figure 6.

Possible role of maternal and/or fetal HPA activation in Human Parturition. HPA, hypothalamus pituitary axis; CAPs, contraction associated proteins; CRH, corticotropin releasing hormone, PGs; Prostaglandins; DS, dehydroepiandrosterone sulfate; 16 OHDS, 16‐hydroxy dehydroepiandrosterone sulfate.

Figure 7.

Pathways affected by various tocolytics used to regulate preterm contractions. AA, arachidonic acid; OTR; oxytocin receptor; FP, PGF receptor; NO, nitric oxide; GTN, glycerine trinitrite; PGI2, prostacyclin.

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References

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Further Reading

Challis JRG, Matthews SG, Gibb W and Lye SJ (2000) Endocrine and paracrine regulation of birth at term and preterm. Endocrine Reviews 21: 514–550.

Gross G, Imamura T and Muglia L (2000) Gene knockout mice in the study of parturition. Journal of the Society for Gynecologic Investigation 7: 88–95.

Keelan J, Blumenstein M, Helliwell R et al. (2003) Cytokines, prostaglandins and parturition – A review. Placenta 24: S33–S46.

Lappas M and Rice GE (2004) Phospholipase A2 isozymes in pregnancy and parturition. Prostaglandins, Leukotrienes and Essential Fatty Acids 70: 87–100.

Lockwood CJ (2002) Biochemical predictors of prematurity. Frontiers of Hormone Research 27: 258–268.

Lopez Bernal A (2003) Mechanisms of labor – biochemical aspects. British Journal of Obstetrics and Gynaecology 110: 39–45.

Myatt L and Lye S (2004) Expression, localization and function of prostaglandin receptors in myometrium. Prostaglandins, Leukotrienes and Essential Fatty Acids 70: 137–148.

Nathanielsz PW, Smith G and Wu W (2004) Topographical specialization of prostaglandin function in late pregnancy and at parturition in the baboon. Prostaglandins, Leukotrienes and Essential Fatty Acids 70: 199–206.

Petraglia F, Florio P, Nappi C and Genazzani AR (1996) Peptide signalling in human placenta and membranes: autocrine, paracrine and endocrine mechanisms. Endocrine Reviews 17: 156–186.

Smith R, Mesiano S and McGrath S (2002) Hormone trajectories leading to human birth. Regulatory Peptides 108: 159–164.

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Gibb, W, and Challis, J R G(Jan 2006) Human Parturition and Birth: Regulation. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0002140]