SUMMARY An association between increased blood pressure and hypalgesia has been reported in several studies in animals and in a few reports in humans. We investigated the relationship between hypertension and pain perception by comparing the response to graded electrical stimulation of the tooth pulp, which is thought to represent an exclusively nodceptive system. The test was performed with a commercial tooth pulp tester in a large series of subjects with borderline or established hypertension and in three groups of normotensive controls: volunteers, nonhypertensive patients, and medical students with a well-established or no family history of hypertension. Subjects had to report when they started to feel pulp stimulation (sensory threshold) and when this became painful (pain threshold). Sensory and pain thresholds were obtained as means of the measurements on four healthy, unfilled teeth. Sensory thresholds were significantly higher hi subjects with borderline or established hypertension than in two of the three normotensive groups (volunteers and normotensive patients), whereas no significant difference was observed between the two hypertensive groups. The results for the pain threshold were qualitatively similar but less dear and less amenable to statistical analysis because this parameter could not be determined with accuracy hi a number of subjects in whom the subjective pain threshold was above the upper range of stimulation of the instrument. The association between Mood pressure levels and pain perception was further confirmed by the highly significant correlation found for the overall data between mean arterial blood pressure and both thresholds. On the other hand, no significant correlation was found with heart rate and no significant effects could be detected by analysis of variance for sex, age, and family history of hypertension. Furthermore, no changes hi pain sensitivity were observed hi a subgroup of patients studied after 3 months of diuretic or ^-blocking treatment or of low salt diet, despite significant reductions of arterial blood pressure. Taken together, our findings provide further confirmatory evidence for an increased tolerance to pain in hypertensive humans and suggest that this may be a feature of arterial hypertension irrespective of the prevailing blood pressure levels. Psychophysiological studies in the rat 2 -9 have demonstrated the association of hypalgesic behavior (delayed response to noxious stimuli such as a hot plate, an electric shock, or a mechanical force applied to a limb) to arterial hypertension. In hypertensive humans, an increased tolerance to pain, as assessed by the measurement of the pain threshold to graded electrical tooth pulp stimulation, has been reported by Zamir and Shuber 10 and confirmed in preliminary studies by our group."•

Pain and depression may share common neurochemical substrates, therefore the study of pain sensation in depression might be valuable in the investigation of the pathophysiology of depression itself. In order to investigate the sensation of pain in depression, we measured pain threshold and sensory threshold by means of a dental tester, comparing a group of depressed patients with healthy volunteers. The results showed the presence of a higher sensory threshold and pain threshold in patients than in controls. This may be related to a hyperfunction of the opiate system, which in turn might be primary or secondary to a decreased modulatory function of other neurotransmitters, in particular of serotonin, whose abnormalities in depressive states are well-documented.

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