Effect of preparturient 17 beta-estradiol and relaxin on parturition and pup survival in the rat.
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.
Cheah
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University of Illinois College of Medicine at Urbana-Champaign 61801.
Sherwood
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D000818:Animals; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D005260:Female; D005313:Fetal Death; D005333:Fetus / Q000187:drug effects*; D007743:Labor, Obstetric / Q000187:drug effects*; D010052:Ovariectomy; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D012016:Reference Values; D012065:Relaxin / Q000494:pharmacology*; D012826:Silicone Elastomers
D012826:Silicone Elastomers; D004958:Estradiol; D012065:Relaxin