title: The persistence of active smooth muscle in the female rat cervix through pregnancy.
abstract: OBJECTIVE
  A controversy exists as to whether functional smooth muscle exists in the cervix before and during pregnancy, potentially continuous with the uterus. We hypothesized that cervical smooth muscle persists through pregnancy and is functional.
  
  
  METHODS
  Uteri and cervices were taken from female virgin, 11 day, and 20 day (near labor) pregnant rats. All experiments used the uterus as a positive control. Three different smooth muscle proteins (smooth muscle α-actin, SM-22α, and calponin-1) allowed immunohistochemical detection of the continuous nature of the smooth muscle from the vagina, cervix, and uterus. Tissues were also hung in isolated tissue baths for the measurement of isometric smooth muscle contraction. Uterine and cervical homogenates were also used in Western analyses to measure protein expression.
  
  
  RESULTS
  Immunohistochemistry revealed there to be smooth muscle as validated by an expression of all 3 markers in the cervix. This smooth muscle was continuous with that of the vagina and uterus. Smooth muscle α-actin was detected in virgin tissue (291.3 ± 32.2 arbitrary densitometry units/β-actin), day 11 (416.8 ± 19.5), and day 20 pregnant tissue (293.0 ± 34.4). The virgin, day 11, and day 20 cervices contracted 2.18 ± 0.24 g, 1.46 ± 0.08 g, and 3.88 ± 0.49 g (respectively) to depolarizing KCl. Cervices contracted at day 20 to the cholinergic muscarinic agonist carbamylcholine (maximum, 133% ± 18.2% KCl contraction, n = 4).
  
  
  CONCLUSIONS
  These findings strongly support that smooth muscle is present in the cervix through pregnancy and continuous with the uterus.
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI.
authors.forename: David J
authors.initials: DJ
authors.lastname: Ferland
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI.
authors.forename: Emma S
authors.initials: ES
authors.lastname: Darios
authors.affiliation: Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI. Electronic address: wattss@msu.edu.
authors.forename: Stephanie W
authors.initials: SW
authors.lastname: Watts
mesh_terms: D000199:Actins / Q000378:metabolism*; D000818:Animals; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D002584:Cervix Uteri / Q000033:anatomy & histology / Q000378:metabolism* / Q000502:physiology; D005260:Female; D007150:Immunohistochemistry; D007537:Isometric Contraction / Q000502:physiology; D008840:Microfilament Proteins / Q000378:metabolism*; D009124:Muscle Proteins / Q000378:metabolism*; D009130:Muscle, Smooth / Q000033:anatomy & histology / Q000378:metabolism* / Q000502:physiology; D011247:Pregnancy / Q000378:metabolism*; D051381:Rats; D014599:Uterus / Q000033:anatomy & histology / Q000378:metabolism / Q000502:physiology; D014621:Vagina / Q000033:anatomy & histology / Q000378:metabolism*; D000096985:Calponins
chemical_list: D000199:Actins; D002135:Calcium-Binding Proteins; D008840:Microfilament Proteins; D009124:Muscle Proteins; D000096985:Calponins; C498862:Acta2 protein, rat; C051615:transgelin
keywords: cervix; pregnancy; rat; smooth muscle