PLASMA-CONCENTRATIONS OF GAMMA-AMINO BUTYRIC-ACID THROUGHOUT HUMAN GESTATION

Objective: Normal pregnant women are characterized by decreases in blo od pressure and dramatic falls in systemic vascular resistance. This v asodilation is lost in pregnancies complicated by proteinuric hyperten sion (preeclampsia). Because gamma-amino butyric acid (GABA) is consid ered to be both an inhibitory neurotransmitter and an antihypertensive amino acid, we hypothesized that GABA levels might increase throughou t gestation and might play a role in the vasodilatory alterations obse rved in normal pregnancy. Methods: Blood samples for measurement of pl asma GABA by high-pressure liquid chromatography (HPLC) were obtained from 4 normal nonpregnant women, from 39 pregnant women at various tim es throughout gestation, and from 5 women with preeclampsia (37-40 wee ks). Results: Normal pregnancy was associated with progressive increas es (p < 0.01) in plasma GABA levels after the first trimester, reachin g maximum values by 27-33 weeks of gestation. In term hypertensive pre gnant women, GABA levels were 13 +/- 3 % lower (p < 0.048) as compared to gestational age-matched controls. During the second and third trim esters of pregnancy, alterations in plasma GABA levels generally mirro r changes in plasma volume and correspond inversely with known cardiov ascular changes, for example, decreases in blood pressure and especial ly systemic vascular resistance. Conclusions: These changes in plasma GABA concentrations suggest a potential role for GABA in modulating ca rdiovascular adaptations in normal pregnancy and a possible role in th e development of pregnancy-induced hypertension.