Further Notes on the Action of Oestrone and Relaxin on the Pelvis of the Spayed Mouse, Including a Single-Dose Test of Potency of Relaxin

Our earlier work on the effect of relaxin upon the symphysis pubis of the mouse was planned with the object of reproducing in the spayed female, during a similar time interval, the changes which take place naturally during the last 6 days of pregnancy and which were described in a previous paper [Hall & Newton, 1946]. We have shown [Hall & Newton, 1947] that daily injections of 0·2 ml. of relaxin extract given for 5 days simultaneously with daily administration of oestrone, after 2 days' priming with oestrone alone, will produce an interpubic separation in spayed animals of the same order as that which occurs at the end of normal pregnancy. During subsequent work it has often been necessary to determine the potency of individual batches of relaxin extract, and it was felt that a more convenient method of assay, involving the use of smaller quantities of extract, was needed.