Pregnant mare's serum (pms) is being used by various workers for inducing ovulation in the immature rat (Cole, 1936; Williams, 1945; Zarrow, Caldwell, Hafez & Pincus, 1958; Strauss & Meyer, 1962; McCormack & Meyer, 1962). This report is concerned with the comparison of pmsg preparations manufactured by three different companies as regards their ability to cause ovarian growth and ovulation in the rat. Also, data relating to the effect of storage on the potency of pmsg are described.
The procedure adopted for standardization of different preparations of pmsg by ovarian weight was that of Cartland & Nelson (1938). Twenty-one-day-old female rats were obtained from the Holtzman Company, Madison, Wisconsin and were maintained on Rockland rat and mouse diet and tap water ad libitum. They were housed in an air-conditioned room (78 to 80° F)