Time course of blood pressure changes after intravenous administration of propranolol or furosemide in hypertensive patients.

The time course of changes in supine and standing blood pressures, heart rate, plasma renin activity, and plasma noradrenaline concentration after intravenous administration of propranolol (0.20 mg . kg-1, with a maximum of 15 mg) or furosemide (40 mg) was studied for a period of 8 h in hypertensive patients. Twenty minutes after intravenous injection of propranolol or furosemide, supine blood pressure was unchanged. Thereafter, blood pressure started to decrease gradually. Maximum reduction was obtained after 4-5 h. Twenty minutes after administration of propranolol, heart rate and plasma renin activity were reduced, and remained so during the following 8 h. Supine plasma noradrenaline concentration did not change significantly after propranolol, but standing levels, showed a tendency to increase as blood pressure fell. Twenty minutes after administration of furosemide, plasma renin activity was increased and remained elevated during the following 8 h. Heart rate and plasma noradrenaline concentration were unchanged after 20 min, but both increased gradually as blood pressure started to fall. The results show that intravenous administration of both propranolol and furosemide leads to a delayed reduction of blood pressure. The increase in total peripheral resistance, which prevents blood pressure from falling acutely after intravenous injection of propranolol, is not reflected in an acute rise in plasma noradrenaline. The delayed hypotensive response does not seem to be due to a return of sympathetic activity to pretreatment levels, since plasma noradrenaline concentration shows a tendency to rise as blood pressure falls.