Attenuation of antepartum relaxin surge and induction of parturition by antiprogesterone RU 486 in sheep.
Pregnant ewes were injected with either the antiprogesterone, RU 486 (4 mg kg-1 body weight, i.m.; n = 5), 3000 iu relaxin (i.m.; n = 9), or diluent (n = 8) at 12:00 h on days 144 and 145, to determine its effect on progesterone and relaxin secretion, and on induction of lambing. RU 486 induced earlier lambing (P < 0.01) compared with diluent treatment, but relaxin treatment did not significantly reduce the interval to parturition. Mean injection-lambing intervals were 31 +/- 2, 109 +/- 23 and 121 +/- 27 h for the RU 486, relaxin and diluent groups, respectively. There was no incidence of difficult birth (dystocia); all lambs were vigorous at birth; and placenta delivery was rapid (within 207 min) with RU 486 and relaxin treatments compared with diluent treated controls. Plasma progesterone concentrations averaged 11 ng ml-1 during the pretreatment period for all animals. RU 486 had a biphasic effect on progesterone concentrations, causing an initial increase (P < 0.05) within 2 h, and then an abrupt drop (P < 0.01) to 6 ng ml-1 by 18:00 h on day 145. Progesterone concentrations remained consistently lower (P < 0.05) in relaxin-treated ewes than in diluent-treated controls from days 144 to 147 and then began a steady decrease to 4 ng ml-1 on the day of parturition (days 149 and 150) in both groups.(ABSTRACT TRUNCATED AT 250 WORDS)
Gazal
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OS
Department of Animal Science, Iowa State University, Ames 50011.
Li
Y
Y
Schwabe
C
C
Anderson
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LL
D000818:Animals; D005260:Female; D007751:Labor, Induced / Q000379:methods / Q000662:veterinary*; D015735:Mifepristone / Q000494:pharmacology*; D011247:Pregnancy; D011374:Progesterone / Q000097:blood / Q000378:metabolism; D012065:Relaxin / Q000097:blood / Q000378:metabolism* / Q000494:pharmacology; D012756:Sheep / Q000502:physiology*
D015735:Mifepristone; D011374:Progesterone; D012065:Relaxin