BIOASSAY OF RELAXIN

IN 1926 Hisaw first demonstrated experimentally the relaxation of the pelvic ligaments of guinea pigs during estrus following the injection of blood serum from pregnant rabbits. Later work indicated a specific hormone, designated as relaxin, was responsible for the looseness of the symphysis pubis, since the effect was also observed following injection of extracts of sow corpora lutea into castrated guinea pigs provided the animals were pretreated with estrogen. Since that time, most of the experimental work on relaxin has been based upon bioassays with this allor- none pelvic looseness endpoint determined by manual palpation. During this assay procedure, the possibility of traumatizing the loosened tissue of the pubic symphysis or exaggerating the hormone-induced separation cannot be excluded. The radiographic measurement of the inter-pubic gap would seem desirable because not only would this provide an objective record but the determination of the actual interpubic distance might provide a more sensitive assay.