Pain sensitivity in silent myocardial ischemia.

Although the cause of silent myocardial ischemia (SMI) is unknown, several theories have been advanced to explain the disorder. Most prominent among these are the suggestions that attribute the condition to generalized impaired pain sensitivity and/or enhanced endorphin activity. The present study examined both hypotheses. It was carried out in 33 patients with myocardial ischemia: 13 with silent myocardial ischemia (silents) and 20 with symptomatic ischemia (symptomatics). Pain sensitivity was determined with thermal, electrical, and ischemic pain tests using signal detection theory (SDT) and conventional threshold procedures. To evaluate the significance of endorphin mechanisms naloxone (6 mg i.v.) and placebo were administered on alternate days in a double-blind, cross-over procedure before the pain tests and again before a treadmill exercise test (TET). Somatic pain sensitivity was found not to be impaired in patients with SMI, and no evidence was found to support a causal role for endorphins in the disorder.

Are runners stoical? An examination of pain sensitivity in habitual runners and normally active controls.

Anecdotal and clinical reports suggest that athletes are stoical. However, there are few studies comparing persons who exercise regularly with those who do not. This study compared two independent samples of regular runners and normally active controls, both without recent exercise, on cold pressor, cutaneous heat, and tourniquet ischemic pain tests. Results demonstrated that the runners' threshold for noxious cold was significantly higher than that of controls. The heart rate and blood pressure responses to cold were similar in the 2 groups, suggesting that differences in cold pain report did not result from differences in autonomic reactivity to cold. Signal detection theory measures demonstrated that runners discriminated among noxious thermal stimuli significantly better than controls, but neither noxious nor innocuous thermal report criteria differed between groups. The cohorts also did not differ in their report of ischemic pain sensations. Thus, these data do not generally support the hypothesis of pain insensitivity or stoicism in habitual runners. Rather, insensitivity occurs only in their response to noxious cold, which is suggested to be an adaptation to regular training.

Pain sensitivity, mood and plasma endocrine levels in man following long-distance running: effects of naloxone.

The effects of intense exercise on pain perception, mood, and plasma endocrine levels in man were studied under naloxone and saline conditions. Twelve long-distance runners (mean weekly mileage = 41.5) were evaluated on thermal, ischemic, and cold pressor pain tests and on mood visual analogue scales (VAS). Blood was drawn for determination of plasma levels of beta-endorphin-like immunoreactivity (BEir), growth hormone (GH), adrenocorticotrophic hormone (ACTH), and prolactin (PRL). These procedures were undertaken before and after a 6.3 mile run at 85% of maximal aerobic capacity. Subjects participated on two occasions in a double-blind procedure counterbalanced for drug order: on one day they received 2 i.v. injections of naloxone (0.8 mg in 2 ml vehicle each) at 20 min intervals following the run; on the other day, 2 equal volume injections of normal saline (2 ml). Sensory decision theory analysis of the responses to thermal stimulation showed that discriminability, P(A), was significantly reduced post-run under the saline condition, a hypoalgesic effect; response bias, B, was unaffected. Ischemic pain reports were significantly reduced post-run on the saline day, also a hypoalgesic effect. Naloxone reversed the post-run ischemic but not thermal hypoalgesic effects. Joy, euphoria, cooperation, and conscientiousness VAS ratings were elevated post-run; naloxone attenuated the elevation of joy and euphoria ratings only. Plasma levels of BEir, ACTH, GH, and PRL were significantly increased post-run. The results show that long-distance running produces hypoalgesia and mood elevation in man. The effects of naloxone implicate endogenous opioid neural systems as mechanisms of some but not all of the run-induced alterations in mood and pain perception.