Cardiovascular responses to circulating catecholamines in normal pregnancy and in pregnancy-induced hypertension

Patients with pregnancy-induced hypertension (PIH) and healthy pregnant and non-pregnant women were compared with regard to cardiovascular responses to i.v. infusions of noradrenaline (NA) and adrenaline (ADR). This resulted in physiologically relevant concentrations in arterial plasma (maximally 10 nmol/litre for NA and 6 nmol/litre for ADR). Non-pregnant women responded to NA with concentration-dependent increases in blood-pressure, which were caused by peripheral vasoconstriction, as systemic vascular resistance (SVR) was increased by 21%. Cardiac output was reduced by 6%. ADR caused concentration-dependent decreases in SVR (to values 36% below basal) and calf vascular resistance (CVR), as well as increases in cardiac output. Healthy pregnant women responded to NA with similar increases in blood-pressure, but this was due to stroke volume-dependent increases in cardiac output (11%) and not due to vasoconstriction. ADR-induced vasodilatation was attenuated in this group. Cardiac responses to ADR were unaffected by pregnancy. PIH patients demonstrated an enhanced systolic blood-pressure response to NA (19% increase vs 7-8% in the other groups) due to the combined effects of vasoconstriction (11% increase in SVR) and an essentially unchanged cardiac output. ADR-induced decreases in CVR and diastolic blood-pressure were similar to those found in the non-pregnant group. Increases in heart rate were less pronounced, but cardiac output increased as normal. These results indicate that normal pregnancy is associated with attenuated vascular responses to circulating catecholamines. PIH patients do not seem to have undergone this normal adaptation of the vascular system to pregnancy.