Dose response of RU486 in a novel rabbit model of noninfectious preterm birth: comparative efficacy of 3 routes of administration.
OBJECTIVE
The purpose of this study was to examine whether the pregnant rabbit model can be used as a viable model for the study of non-infection-mediated preterm birth.


METHODS
Timed pregnant New Zealand rabbits were injected with a single dose of RU486 on day 22 of gestation. Three doses (50 mg, 75 mg, and 100 mg) were administered intramuscularly, intraperitoneally, or subcutaneously. The rabbits were monitored for preterm delivery. Progesterone, cortisol, and cytokine levels were examined before the induction and after delivery. Uterine and cervical progesterone, cortisol, and cytokine levels were determined after delivery.


RESULTS
RU486 resulted in 100% preterm delivery in all doses and modes of administration, compared with 0% of controls. Intramuscular administration appeared to generate the most favorable preterm delivery time. Rabbits that received 100 mg RU486 intramuscularly showed significantly decreased serum progesterone levels and uterine progesterone levels, compared with 100 mg subcutaneously and intraperitoneally.


CONCLUSIONS
RU486 that was administered intramuscularly appears to be a potent and effective method for inducing preterm birth. This model of hormonally mediated preterm birth might serve as a useful model for the investigation of the possible mechanisms of preterm labor.
Gorenberg
David
D
Division of Maternal-Fetal Medicine, Women's Hospital, Long Beach, California, USA. david_gorenberg@pediatrix.com
Beharry
Kay
K
Nishihara
Kenji C
KC
Chang
Eileen
E
Waltzman
Joshua
J
Akmal
Aamir
A
Asrat
Tamerou
T
D000021:Abortifacient Agents, Steroidal / Q000008:administration & dosage*; D000818:Animals; D016207:Cytokines / Q000032:analysis; D004195:Disease Models, Animal; D005260:Female; D006854:Hydrocortisone / Q000032:analysis; D007273:Injections, Intramuscular; D007274:Injections, Intraperitoneal; D007279:Injections, Subcutaneous; D015735:Mifepristone / Q000008:administration & dosage*; D011247:Pregnancy; D047928:Premature Birth / Q000139:chemically induced*; D011374:Progesterone / Q000032:analysis; D011817:Rabbits
D000021:Abortifacient Agents, Steroidal; D016207:Cytokines; D015735:Mifepristone; D011374:Progesterone; D006854:Hydrocortisone