Effect of preparturient 17 beta-estradiol and relaxin on parturition and pup survival in the rat

Endocrinology. 1988 May;122(5):1958-63. doi: 10.1210/endo-122-5-1958.

Abstract

This study examined the requirement for 17 beta-estradiol (E) and relaxin (R) during the preparturient period (approximately the last 30 h of gestation) for normal parturition and pup survival in the rat. On the evening of day 21 of pregnancy, primiparous Sprague-Dawley rats were bilaterally ovariectomized or sham operated and fitted with Silastic capsules containing one of four doses of E (6.0, 11.4, 45.6, or 68.4 micrograms in sesame oil) or sesame oil only. These rats were also injected sc with either 200 micrograms highly purified porcine R dissolved in 200 microliter 5% beeswax in corn oil or R vehicle three times (approximately 8 to 10-h intervals) beginning at ovariectomy. The durations of straining and delivery were increasingly prolonged with increasing doses of E in the ovariectomized groups that received E but no R. In rats that received the two highest doses of E there was a reduction in the percentage of pups born alive and a reduction in pups surviving on day 2 postpartum, and one or two undelivered fetuses were retained in utero in some animals 3 days postpartum. The administration of R with the two highest doses of E restored all parturition parameters to values not different from those of intact controls. In the absence of both E and R, all measured parturition parameters were abnormal, and administration of R in the absence of E only partially restored them to control values. Two major conclusions are drawn. First, E treatment alone to pregnant rats ovariectomized on day 21 fails to elicit normal parturition; indeed, with increasing doses of E, parturition parameters and pup survival become increasingly adversely affected. Second, R treatment of E-treated ovariectomized rats during the immediate preparturient period restores parturition parameters and pup survival to the levels of intact sham-operated controls.

Publication types

  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • Animals
  • Estradiol / blood
  • Estradiol / pharmacology*
  • Female
  • Fetal Death
  • Fetus / drug effects*
  • Labor, Obstetric / drug effects*
  • Ovariectomy
  • Pregnancy
  • Rats
  • Rats, Inbred Strains
  • Reference Values
  • Relaxin / pharmacology*
  • Silicone Elastomers

Substances

  • Silicone Elastomers
  • Estradiol
  • Relaxin