Comparative study of normotensive and hypertensive nitric oxide synthase inhibitors on morphine withdrawal syndrome in rats.

The effects of the normotensive, mainly centrally active nitric oxide synthase (NOS) inhibitor 7-nitro indazole and the hypertensive drug NG-nitro-L-arginine, which blocks both the endothelial and the central NOS, have been examined on naloxone-precipitated withdrawal in morphine-dependent rats. Both drugs attenuated the same withdrawal signs (teeth-chattering, penile licking, diarrhoea, chewing, wet-dog shakes, grooming), while other signs remained unaffected (rearing, jumping, ptosis, rhinorrhoea, irritability on touch). These findings indicate that mainly central (but not endothelial) nitric oxide is involved in the expression of some opioid withdrawal symptoms.