Circulatory and metabolic effects of a combined alpha‐ and beta‐ adrenoceptor blocker (labetalol) in hypertension of pregnancy.

1 Seven women with hypertension of pregnancy were given the combined alpha- and beta-adrenoceptor blocking drug labetalol (50 mg i.v.) in their last trimester. Acute effects were studied for 3 h after administration. 2 Systolic and diastolic blood pressures were significantly reduced from 143 +/- 4 (s.e. mean) to 127 +/- 5 mmHg and from 101 +/- 2 to 88 +/- 2 mmHg, respectively. Maternal heart rate fell significantly from 77 +/- 5 to 68 +/- 3 beats/min. The changes remained during the 3 h of observation. Foetal heart rate was not affected. No side-effects were encountered. 3 Plasma noradrenaline increased significantly from 1.54 +/- 0.16 to a peak value of 2.37 +/- 0.41 nmol/l suggesting sympathetic activation following labetalol. Plasma adrenaline levels were essentially unchanged. Plasma glucose, insulin and C-peptide showed only minor changes. No major effects on lipid metabolism were seen except a significant fall of nonesterified fatty acids at 60 min. Plasma cyclic AMP increased significantly throughout the observation period, perhaps indicating beta-adrenoceptor agonist activity of labetalol. 4 The effectiveness of labetalol as an acute hypertensive agent together with apparent absence of metabolic disturbances and other side-effects makes it an interesting drug for the treatment of hypertension during pregnancy.