Circadian rhythms of blood pressure and pressor hormones in normal and hypertensive pregnancy.

1. Circadian patterns of blood pressure and pressor hormones were studied in late pregnancy in ten normotensive women and twenty-one hypertensives. 2. Plasma renin activity, angiotensin II and free adrenaline and noradrenaline leves were highest at 0900 h in normotensives and uncomplicated hypertensives. Catecholamine sulphate levels were lowest at 0900 h. 3. In eight pre-eclamptic hypertensives, plasma renin activity, and angiotensin II were suppressed. 4. Adrenaline sulphate levels were raised in hypertensives. 5. Four pre-eclamptics with noctural hypertension had the highest blood pressures; their diurnal rhythm for noradrenaline sulphate was reversed but they showed no consistent pattern of pressor hormones. However failure of angiotensin II, adrenaline or noradrenaline to fall at night in subjects with increased vascular reactivity could contribute to their nocturnal hypertension.