Modulation of pain perception by ramipril and losartan in human volunteers.

The angiotensin converting enzyme inhibitors (ACEIs) and angiotensin receptor blockers (ARBs) are a well known entity and have been used in therapeutics for various indications like hypertension, myocardial infarction and CHF. However, there is a renewed interest in these compounds in terms of their effects on pain perception in animals as well as in human beings. They have yielded contradictory results, showing hyperalgesia in some studies but analgesia in others. Hence this study was undertaken to evaluate the effect of Ramipril (an ACE-I) and Losartan (an ARB) on pain perception in human volunteers using cola caps and handcuff of sphygmomanometer. A total of 30 healthy, normotensive individuals with no previous history of intake of analgesics during or 4 weeks prior to the study were selected after an informed consent. The first group received a single dose of placebo, the second group received Ramipril (2.5 mg) & the third group received Losartan (50 mg). Pain perception threshold (the point at which an individual first experiences pain) and the maximum tolerated pain were assessed using the above method. The control group showed no significant changes in pain threshold, but the group receiving either Ramipril or Losartan showed a decline in threshold for maximum tolerated pain. Only Ramipril and not Losartan decreased the pain perception threshold. Our study revealed that single dose treatment of healthy volunteers with Ramipril and Losartan may cause algesia as early as after ingestion of the first dose and further studies are needed to study their long term effects on pain perception.