Diamine oxidase in human pregnancy. Plasma diamine oxidase in nonpregnant and normal pregnant patients

Plasma diamine oxidase was measured in 72 nonpregnant patients and during normal pregnancy with the use of a recently developed radioassay procedure. The mean level of plasma diamine oxidase in the normal nonpregnant state was found to be 3.4 units with a standard deviation of plus or minus 1.5 units. In the group of nonpregnant patients with a variety of disease states, there were 5 instances, including 3 cases of Laennec's cirrhosis, in which the plasma titer of the enzyme was considerably greater than the mean for the group. A sharp rise in plasma diamine oxidase occurred in pregnant patients approximately 5 to 6 weeks following the last normal menstrual period and rapidly reached a plateau where it remained until parturition. The plasma enzyme activity following parturition did not reach normal nonpregnancy levels for approximately 10 to 14 days, and the rate of decline was not influenced by the removal of the uterus. The large maternal to fetal ratio of plasma diamine oxidase, as well as the normal nonpregnancy levels in a case of choriocarcinoma, suggested that the source of the enzyme is the maternal placenta.