The effects of sodium loading on blood pressure and pain responses to the cold pressor test.

Two cold pressor tests were administered to 18 healthy normotensive males on two occasions, after 2 weeks of dietary sodium loading and after 2 weeks of maintaining their normal diet. While the addition of an extra 10 g/day of sodium to the diet had no overall effect on resting cardiovascular activity, it produced significantly greater diastolic blood pressure and smaller heart rate responses to the pain stimuli. As well, consistent with the large animal literature indicating a relationship between high blood pressure and diminished pain sensitivity, pain ratings were found to be significantly lower during the sodium loaded testing session. The ratings were corroborated by evidence of lower skin conductance reactivity to the second cold pressor test in the sodium loaded condition. Information concerning an elevation of risk for hypertension, perhaps provided by baroreceptors, may lead to compensatory reactions with hypoalgesia as one effect.