Naloxone increases blood flow in the human hand.

Intravenous injection of 2 mg naloxone produced a rapid and pronounced rise of blood flow (6.3 +/- 5.0 to 67.0 +/- 15.1 ml min-1 100 ml-1) and skin temperature (28.3 +/- 3.0 to 32.4 +/- 1.2 degrees C) in the finger and hand of seven of ten normal volunteers. In the other three there was only a small response. Skin temperature did not change in either the face or the foot. Three responding subjects who were retested with 0.4 mg naloxone showed a smaller and briefer response. To exclude a local effect of naloxone on skin blood flow due to release of histamine, responders and non-responders were tested with naloxone and morphine pricked into the skin of the hand and forearm. All showed a weal and flare reaction to morphine which was not abolished by mixture with naloxone; none showed any reaction to naloxone alone. These results suggest that, in some subjects at least, skin blood flow in the hand may be under endogenous opioid control and they raise the possibility that opioid antagonists might have value in the treatment of disorders of skin blood flow such as Raynaud's disease.