1. Haemodynamic and hormonal actions of 100 mg of captopril (SQ 14 225) orally were tested in 12 healthy volunteers with and without indomethacin pretreatment.
2. Without indomethacin, mean arterial blood pressure was reduced at 30 and 60 min after captopril (P < 0.02). Heart rate did not change. Plasma renin activity (PRA) increased (P < 0.002), and plasma and urinary aldosterone as well as plasma 18-hydroxycorticosterone (18- OH-B) decreased after captopril (P < 0.02). Prostaglandin (PG) E2, kallikrein, urine volume, sodium and potassium excretion rates remained constant after captopril.
3. Under indomethacin pretreatment, blood pressure was reduced to a smaller degree at 30 and 60 min after captopril (P < 0.05). Heart rate was constantly lower than without indomethacin (P < 0.05). Indomethacin decreased basal PGE2 and kallikrein excretion (P < 0.02) and reduced basal PRA as well as the increase of PRA after captopril (P < 0.05). Basal mineralocorticoid levels were significantly lower than without indomethacin. Aldosterone did not decrease further after captopril, and 18-OH-B fell only slightly.
4. The results suggest that prostaglandins may be involved in the haemodynamic and hormonal actions of captopril.
