Plasma vasopressin concentrations and serum vasopressinase activity in pregnant and nonpregnant women.

Vasopressin (AVP) concentration was measured by radioimmunoassay from unextracted plasma of nonpregnant women and during first and third trimester of pregnancy. In nonpregnant state it was 3.5 +/- 0.6 pg/ml, in first trimester 4.3 +/- 1.8 pg/ml, but in third trimester 6.5 +/- 0.4 pg/ml and significantly (p less than 0.001) higher than in nonpregnant state. AVPase activity was investigated by in vitro method whereby the decrease of AVP concentration during incubation was measured. In first trimester pregnancy, the AVPase activity was 3-fold and in third trimester 20-fold when compared with nonpregnant level.