Study of angiotensin converting enzyme (ACE) inhibitory effects of main Papaver spp. alkaloids

Angiotensin converting enzyme (ACE) converts the inactive angiotensin I to (a potent vasoconstrictor and aldosterone releaser) angiotensin II. Inhibitors of ACE are valuable drugs in the treatment of hypertension, and heart failure. These inhibitors have a natural origin and non-peptide drugs were synthesized from the natural lead compounds. However, because of some side effects such as dry cough, many investigators are searching in natural products to find better and more selective lead compounds. There are reports on the interaction between rennin-angiotensin system and endogenous opioid system. Morphine and endogenous opioids have reported to inhibit ACE. In this research we examined the possible inhibitory effects of purified papaver’s main alkaloids on the activity of purified rabbit lung ACE. We found that only papaverin at 1 mM inhibited the enzyme by 40%. The Km value of ACE increased while Vmax decreased in papaverin treated samples. We conclude that part of hypotensive effects of papaverin may be related to ACE inhibition, and this compound will be a suitable lead compound for further investigation.