Endocrinology, Vol 123, 2486-2490, Copyright © 1988 by Endocrine Society

ARTICLES

Monoclonal antibodies specific for rat relaxin. III. Passive immunization with monoclonal antibodies throughout the second half of pregnancy reduces cervical growth and extensibility in intact rats

JJ Hwang and OD Sherwood
Department of Physiology and Biophysics, University of Illinois, Urbana 61801.

Relaxin is required for normal delivery in the rat. The mechanism(s) whereby relaxin contributes to rapid and safe delivery of the fetuses, however, has not been established. The purpose of this investigation was to determine if relaxin enables normal delivery by promoting the growth and modifying the tensile properties of the uterine cervix. To that end, a monoclonal antibody specific for rat relaxin, designated MCA1, was used to passively neutralize endogenous relaxin in intact pregnant rats. MCA1 or PBS vehicle was administered iv to rats daily from days 12-22 of pregnancy. Cervices were removed at 1200 h on day 22. Cervices obtained from MCA1-treated rats were much smaller and far less extensible than cervices obtained from control rats. Moreover, cervices from MCA1-treated rats were less able to accommodate stress created by extension than cervices from control rats. Passive neutralization of relaxin had no influence on 1) the weights of other reproductive tissues (uterus, placenta, and ovary), 2) the number of fetuses, and 3) the viability of fetuses. The present study indicates that in the rat endogenous relaxin is required for promoting cervical growth and softening during the second half of pregnancy. This work supports the hypothesis that the influence of endogenous relaxin on birth is attributable, at least in part, to its effects on the cervix.

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