Hypertension inhibits noxious-evoked c-fos expression in the rat spinal cord

The effect of hypertension on spinal induction of the c-fos proto-oncogene following noxious mechanical stimulation of the skin was studied in the rat. The occlusion of renal artery raised blood pressure steeply, reaching 52% over initial values. Oral administration of NG-nitro-L-arginine methyl ester provoked a gradual increase in blood pressure which reached up to 62%. The numbers of spinal dorsal horn Fos-immunoreactive nuclei were reduced to 66% and 38% of controls in animals with renal- and pharmacologically-induced hypertension, respectively. These data indicate that hypertension is accompanied by an inhibition of spinal nociceptive neurones which probably accounts for the hypoalgesia observed in hypertensive subjects. They further suggest an influence by the rate of increase of blood pressure on the level of spinal inhibition.