Natural painkillers linked to high blood pressure

Opioid hormones, which are naturally produced by the body to reduce pain, may be involved in changes in both pain sensitivity and blood pressure among people with early-stage hypertension.

"Persons with hypertension have reduced pain sensitivity," Dr. James A. McCubbin told Reuters Health. "This pattern also emerges in young people at risk for hypertension, suggesting that altered pain sensitivity may have a role in the early development of this disease," he added.

However, the exact relationship between pain perception and altered blood pressure control is not clear, McCubbin, from Clemson University in South Carolina, and his colleagues note in the medical journal Psychosomatic Medicine.

McCubbin's team examined the effects of natural opioids, such as endorphins and enkephalins, on pain perception and blood pressure in 125 young adults with mildly elevated blood pressure. On separate occasions, subjects were given the opioid blocker, naltrexone, or placebo 60 minutes before their pain threshold was tested by immersing their dominant hand in ice water for two minutes or as long as they could bear.

The results, report the researchers, support the idea that blood pressure goes up as pain sensitivity goes down - whether or not natural opioids are blocked. This indicates that both opioid and non-opioid analgesic mechanisms are linked to blood pressure.

Additionally, McCubbin's team observed that subjects with high-normal blood pressure have diminished sensitivity to pain, which is reversed by opioid blockade. "This indicates a greater degree of opioid analgesic tone in young persons at risk for hypertension," they point out.

Summing up, McCubbin and colleagues say evidence from this study, as well as several others, suggests that natural opioid pain-lowering mechanisms "are deranged in the early stages of hypertension" and might be a cause of increased blood pressure.

"Better understanding of the effects of opioid hormones on pain sensitivity and blood pressure may lead to novel prevention and treatment strategies for hypertension and related cardiovascular diseases," McCubbin said.

SOURCE: Psychosomatic Medicine, January/February 2006.