Endogenous opioids, blood pressure, and diffuse noxious inhibitory controls: a preliminary study.

A 2003 study suggested that there are age differences in diffuse noxious inhibitory controls (DNIC), a form of endogenous pain inhibition. The present report describes a followup study employing a pharmacological blockade of endogenous opioids, i.e., using naloxone, in a small subset (n=6) of healthy young volunteers to characterize the opioid-dependence of DNIC, as well as DNIC's association with cardiovascular reactivity. Findings suggested that, while opioid blockade enhanced cardiovascular reactivity to cold pain, DNIC was not affected by administering naloxone. Interestingly, greater cardiovascular responses to noxious cold were associated with enhanced DNIC in this small sample. This relationship, which did not appear opioid-dependent, supports previous models integrating cardiovascular activity with the functioning of pain-modulatory systems.