Endocrinology, Vol 122, 1958-1963, Copyright © 1988 by Endocrine Society

ARTICLES

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

SH Cheah and OD Sherwood
University of Illinois College of Medicine at Urbana-Champaign 61801.

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.

This article has been cited by other articles:

				E. H. Luque,, M. M. Muñoz de Toro,, J. G. Ramos,, H. A. Rodriguez,, and O. D. Sherwood Role of Relaxin and Estrogen in the Control of Eosinophilic Invasion and Collagen Remodeling in Rat Cervical Tissue at Term Biol Reprod, October 1, 1998; 59(4): 795 - 800. [Abstract] [Full Text]

				L. L. Burger and O. D. Sherwood Relaxin Increases the Accumulation of New Epithelial and Stromal Cells in the Rat Cervix during the Second Half of Pregnancy Endocrinology, September 1, 1998; 139(9): 3984 - 3995. [Abstract] [Full Text] [PDF]