THE EFFECTS OF PREGNANCY AND RELAXIN ON THE HISTOLOGY OF THE PUBIC SYMPHYSIS IN THE MOUSE

Abstract

During pregnancy in the mouse the pubic bones become separated, and the gap is bridged by a ligament which at parturition may be 5 or 6 mm. long [Gardner, 1936]. The normal course of separation of the two bones in pregnant mice has been described in a previous paper [Hall & Newton, 1946a]. The bones begin to separate on the 13th day of pregnancy, and the gap widens an average of 1 mm. per day until parturition, which normally takes place during the night following the 19th day. After this the gap rapidly closes, is usually less than 2 mm. on the 3rd or 4th day post partum, but does not completely return to the virgin condition. The changes which occur during pregnancy can be produced in the spayed mouse by the administration of an extract of pregnant rabbit serum (shown by Hisaw [1926] to contain relaxin), accompanied by