Regulation of relaxin secretion.

Relaxin and estrogen reduced the resistance to dilatation of the mouse cervical canal. Relaxin was stored in, and secreted from , the ovaries of pregnant mice. The corpus luteum of gravid women just at delivery contained 25-50 GPU/g of relaxin, while the placenta, amniotic fluid and serum had no relaxin activity. Luteinizing hormone, luteotropic hormone and oxytocin effected elongation of the interpubic ligament of pregnant mice and seemed to regulate relaxin secretion. Puerperal regression of the interpubic ligament may be induced by decrease in relaxin content in the ovary, by decrease in relaxin activity in association with deficient estrogen and by increase in pressure upon the cervical canal.