Catecholamine responses to changes in posture during human pregnancy.

Human pregnancy may induce changes in the sensitivity of the cardiovascular system to endogenous catecholamines. This was investigated in multigravid women with little likelihood of unsuspected vascular disease. The responses of blood pressure, pulse rate, plasma noradrenaline and adrenaline to a change in posture from semi-recumbency to standing were assessed in six normotensive women at 36 weeks gestation and in six non-pregnant control subjects. Standing for 10 min caused a surge in blood pressure, pulse rate and plasma noradrenaline in non-pregnant women. The pregnant women, whose basal levels of noradrenaline were higher than those in non-pregnant women, showed a slower noradrenergic response to postural change, and this response had less effect upon the cardiovascular indices. Blood pressure dropped immediately on standing and pulse rate remained unaffected throughout. It is suggested that some women may maintain a non-pregnant level of pressor sensitivity during pregnancy and thereby become hypertensive.