Thromb Haemost 1990; 63(03): 349-355
DOI: 10.1055/s-0038-1645045
Original Article
Schattauer GmbH Stuttgart

The Increased Rate of Activation of Factor XII in Late Pregnancy Can Contribute to the Increased Reactivity of Factor VII

K A Mitropoulos
The MRC Epidemiology and Medical Care Unit, Northwick Park Hospital, Harrow, Middlesex, Oxford, U. K.
,
J C Martin
The MRC Epidemiology and Medical Care Unit, Northwick Park Hospital, Harrow, Middlesex, Oxford, U. K.
,
A I Burgess
*  Nuffield Department of Clinical Biochemistry, The Radcliffe Infirmary, Oxford, U. K.
,
M P Esnouf
*  Nuffield Department of Clinical Biochemistry, The Radcliffe Infirmary, Oxford, U. K.
,
Y Stirling
The MRC Epidemiology and Medical Care Unit, Northwick Park Hospital, Harrow, Middlesex, Oxford, U. K.
,
D J Howarth
The MRC Epidemiology and Medical Care Unit, Northwick Park Hospital, Harrow, Middlesex, Oxford, U. K.
,
B E A Reeves
The MRC Epidemiology and Medical Care Unit, Northwick Park Hospital, Harrow, Middlesex, Oxford, U. K.
› Author Affiliations
Further Information

Publication History

Received 26 October 1989

Accepted after revision 23 January 1990

Publication Date:
30 June 2018 (online)

Summary

The amidolytic activity of enzymes derived from factor XII (XIIa) was 3-fold higher in plasmas collected during pregnancy than from control subjects. Factor VII coagulant activity (VIIc) and XIIa increased in both kinds of plasmas on incubation on ice for 24 h (cold activation). These increases could be attributed to the decreased potency of C1 inhibitor (C1INH). However, variations in the concentration of C1INH and of factor XII could not explain the differences in VIIc and in XIIa between late pregnancy and control plasmas following cold activation under the same conditions. It is concluded that in vitro the increased amount of contact surface in the late pregnancy plasma promotes a higher rate of generation of XIIa and consequently a higher rate of activation of factor VII. The increased amount of contact surface could also be responsible for the increased concentration of XIIa in non-treated plasma from late pregnancy and could contribute in vivo to the higher reactivity of factor VII in this condition.