title: Effect of multiparity on morphometry and oestrogen receptor expression of pelvic and perineal striated muscles in rabbits: is serum oestradiol relevant?
abstract: OBJECTIVE
  To determine changes in morphometry and expression of oestrogen receptors (OR) in the pubococcygeus and bulbospongiosus muscles, and the concentration of serum oestradiol associated with multiparity.
  
  
  METHODS
  Twelve chinchilla-breed female rabbits were divided into multiparas who had undergone four consecutive deliveries and age-matched virgin nulliparas. Pubococcygeus and bulbospongiosus muscles were surgically removed from each rabbit and processed histologically. Fibre cross-sectional area, number of peripheral nuclei, and expression of ORα and ORβ were measured for each muscle. Serum samples were obtained and the concentration of serum oestradiol was quantified.
  
  
  RESULTS
  Multiparity increased (p ≤ 0.05) fibre cross-sectional area and the number of peripheral nuclei per fibre in pubococcygeus muscle, but not in bulbospongiosus muscle. Expression of both ORα and ORβ was high (p ≤ 0.05) in both muscles from multiparous rabbits. A rise in serum oestradiol was measured at the end of the second pregnancy, which was absent (p ≤ 0.05) at the end of the fourth pregnancy. The concentration of serum oestradiol was similar (p > 0.05) in nulliparous and multiparous rabbits.
  
  
  CONCLUSIONS
  Multiparity caused morphometric changes in pubococcygeus muscle but not in bulbospongiosus muscle. As OR expression was high for both muscles, some properties related to fibre composition or muscle physiology could be affected. The finding that serum oestradiol was not elevated at the end of the fourth pregnancy could be related to changes in pelvic and perineal muscles associated with multiparity.
authors.affiliation: Centro Tlaxcala de Biología de Conducta, Universidad Autónoma de Tlaxcala, Tlaxcala, Tlaxcala, Mexico.
authors.forename: K
authors.initials: K
authors.lastname: López-García
authors.lastname: E Cuevas
authors.forename: D L
authors.initials: DL
authors.lastname: Corona-Quintanilla
authors.forename: I
authors.initials: I
authors.lastname: Jiménez-Estrada
authors.forename: M
authors.initials: M
authors.lastname: Martínez-Gómez
authors.forename: F
authors.initials: F
authors.lastname: Castelán
mesh_terms: D000818:Animals; D004958:Estradiol / Q000097:blood*; D047628:Estrogen Receptor alpha / Q000096:biosynthesis*; D047629:Estrogen Receptor beta / Q000096:biosynthesis*; D005260:Female; D018485:Muscle Fibers, Skeletal / Q000648:ultrastructure; D018482:Muscle, Skeletal / Q000502:physiology* / Q000648:ultrastructure; D010298:Parity / Q000502:physiology*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011817:Rabbits
chemical_list: D047628:Estrogen Receptor alpha; D047629:Estrogen Receptor beta; D004958:Estradiol