Plasma and platelet norepinephrine in normal and preeclamptic pregnancy.

Catecholamines accumulate in platelets, and platelet catecholamine concentrations may give a more stable index of sympathoadrenal activity than do random plasma values. We measured norepinephrine in plasma and platelets from normal, nonpregnant women and from normal and preeclamptic pregnant women with a radioenzymatic assay. Plasma and platelet norepinephrine was not markedly different in normal, pregnant women during the third trimester, intrapartum or postpartum when compared with those levels in nonpregnant women. Platelet norepinephrine was significantly elevated in women with mild preeclampsia, but plasma norepinephrine was not. A linear relationship existed between platelet count and platelet norepinephrine concentrations in women with preeclampsia. These findings are compatible with the hypothesis of increased sympathoadrenal activity in women with mild preeclampsia and normal platelet counts. The lower platelet norepinephrine in thrombocytopenic patients suggests that platelet activation and degranulation have occurred and indicate that platelet catecholamine concentration does not provide a stable index of sympathoadrenal activity when platelets are being consumed.