BIOLOGICAL ACTIVITY OF CERTAIN PROGESTERONE-LIKE COMPOUNDS AS DETERMINED BY THE HOOKER-FORBES BIOASSAY*

Abstract

PROGESTERONE is unique among steroids in that it is the only progestational hormone characterized from biological sources. There is reason to believe, however, that other substance(s) with this type of activity may be present (1). Bioassays of peripheral blood of pregnant ewes (2) and human beings (3) by the method of Hooker and Forbes indicate levels of as much as 10µg. per ml. and 2µg. per ml., respectively. However, chemical extraction of peripheral blood for progesterone resulted in levels which were not measurable (less than 0.1µg. per ml. of plasma) in the ewe (4), and an average of 0.08µg. per ml. of blood in the human being (1, 5). By isotopic dilution it was shown that pooled human pregnancy plasma obtained during the second and third trimesters contained 0.08µg. per ml. of plasma (1). From these data it would appear that the presence of another substance active in the Hooker-Forbes bioassay must be suspected.