Histaminase and Histamine in Normal and Toxaemic Pregnancy

Abstract

Although the blood histamine concentration during normal pregnancy is within the normal range, the serum histaminolytic power is greatly increased (1-3). This remark able increase in serum histaminolytic power is much more characteristic of pregnancy in man than in any other animals (4). The increase in serum histaminase activity starts as a rule during the second or third month, reaching a maximum in the fifth to the seventh month at which level it remains with modest variations until full term. It then rapidly returns within 3 or 4 days postpartum to the negligible values as found in normal non pregnant women (2).The placenta is very rich in histaminase activity (5) and is the principal source of in creased serum enzyme activity (6). Pathological changes in the placenta can, therefore, be expected to produce alterations in the normal pattern or sequence of changes in the serum histaminolytic power during pregnancy.Lindberg (6) recently showed that an intravenous infusion of histamine resulted in a lower concentration of histamine in blood when a woman was pregnant, and that ad ministration of aminoguanidine, an inhibitor of histaminase, to pregnant women raised the concentration of histamine in blood (7).It has been suggested that deviations from the normal pattern of increase in serum histaminase activity are indicative of an abnormal pregnancy (1), and variable changes in the enzyme activity in cases of pre-eclampsia have been reported (8). Studies on urinary excretion of histamine in cases of pre-eclampsia (9) suggest that there is increased con centration of histamine in circulation under this condition.Until recently, it has been thought that serum histaminase estimations might possibly serve to indicate indirectly the histamine content of blood, and that the high histaminolytic power of blood could thus be satisfactorily correlated with the common clinical observa tion of remission of allergic manifestations during pregnancy. Hopes were entertained of throwing light on the significance of tissue and blood histamine via studies of this factor, in the same way that studies of acetylcholinesterase have yielded valuable information on the functions of acetylcholine in the body. The reported similarities between lesions pro duced by experimental poisoning with histamine in pregnant animals and the clinico-pa thological features of pre-eclampsia and eclampsia, and the partly difect and partly in direct evidences that have accumulated pointing toward an excess of circulating histamine in pre-eclampsia and eclampsia together with the establishment of the fact that histamine produces definite hypertensive effects under certain conditions have stimulated our interest in the study of the problem of histamine metabolism in normal and toxaemic pregnancy, and have led to the hypothesis that histamine plays a decisive role in the aetiology of pre eclampsia and eclampsia, which has, hitherto, eluded discovery despite extensive research in the past six decades.It seemed desirable from the foregone facts to investigate in...

Actions of Histamine on Human, Sheep and Monkey Umbilical Vasculature

“…Whether these findings have any con nection with the role of histamine on the fetal circulation is unclear. But, recent studies did reveal that in preeclampsia and eclampsia there was an increase in maternal serum histamine associated with the decreased enzyme levels [1]. Unfortunately, fetal histamine blood levels were not ascertained.…”