Abstract

THE response of the pubic symphysis of the estrogen-primed mouse to relaxin-containing extracts of pregnant rabbit serum (PRS) and of pregnant sow ovaries (PSO) has been reported previously (Kliman, Salhanick and Zarrow, 1953). Significant symphyseal separations were obtained with both types of extracts, although some differences were noted in the slopes of the dose-response curves of preparations from each of these two sources. However, roentgenographic measurement of the average increments in pubic separation produced by single doses of such extracts gave reliable quantitative determinations of activity. The effectiveness of crude extracts was confirmed by their ability to produce significant relaxation in all treated mice, and to reproduce the rate of separation which normally occurs during pregnancy.

Subsequently, studies were made of the action, on the pubic symphysis of the mouse, of relaxin preparations of different specific activities. It has been found that some preparations which are very potent in the guinea pig

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