Nociception and baroreceptor stimulation in hypertension-prone men and women MUSTAFA AL’ABSI, a CHRISTOPHER R. FRANCE, b CHRISTOPHER RING, c JANIS FRANCE, b ANGIE HARJU, a DAVID MCINTYRE, c and LORENTZ E. WITTMERS a a University of Minnesota Medical School, Duluth, Minnesota, USA b Department of Psychology, Ohio University, Athens, Ohio, USA c Department of Sport and Exercise Sciences, University of Birmingham, Birmingham, England Abstract We examined the effects of baroreceptor stimulation on nociceptive responding in men and women with a positive or negative parental history of hypertension. The effects of three baroreceptor conditions (stimulation, inhibition, and control) on subjective pain and nociceptive responding were evaluated during electrocutaneous sural nerve stimulation. Pain ratings were lower in men with positive parental history relative to men with negative parental history, but this difference was not found in women. Both stimulatory and inhibitory baroreceptor conditions were associated with reduced pain reports compared to the control condition. There were no significant differences in nociceptive re- sponding as a function of parental history of hypertension. Although this study confirms a link between hypoalgesia and risk for hypertension in men, it does not support the hypothesis that this attenuated pain perception is due to enhanced baroreceptor activity. Descriptors: Pain, Hypertension, Baroreflex, Gender, Nociceptive flexion This study was conducted to assess the effects of baroreceptor stimulation on nociception and pain in normotensive men and women at risk for hypertension and to evaluate sex differences in response to baroreceptor stimulation. Experiments have shown that baroreceptor stimulation attenuates pain sensitivity (Dwor- kin et al., 1994; Dworkin, Filewich, Miller, & Craigmyle, 1979). On the other hand, accumulated research suggests a link between high blood pressure and pain sensitivity in animals and humans. Spontaneously hypertensive rats exhibit elevated pain thresholds in response to electric shock, hot plate, and tail flick (Maixner, Touw, Brody, Gebhart, & Long, 1982; Saavedra, 1981). Use of pharmacological agents to increase blood pressure (e.g., phenyl- ephrine) has also been associated with an increase in pain tol- erance in animal studies (Randich & Maixner, 1986). In humans, hypertensive patients have higher pain thresholds during electri- cal stimulation of tooth pulp or noxious thermal stimulation when compared to normotensive controls (Ghione, 1996; Zamir & Shuber, 1980). One of the mechanisms that has been proposed to explain blood pressure related hypoalgesia is enhanced baroreceptor stimulation (France, 1999). This enhanced activation may result from increased hypothalamic-autonomic activation (al’Absi & Lovallo, 1993; Anderson, Sinkey, Lawton, & Mark, 1989), in- cluding sympathetic activation leading to increased blood pres- sure reactivity. Increased blood pressure, in turn, may lead to enhanced activation of baroreflex-mediated pain attenuation in hypertension-prone individuals (Ghione, 1996; Guasti et al., 2002). This is consistent with previous studies demonstrating enhanced cardiovascular and adrenocortical responses to psy- chological stress in these individuals (al’Absi, Lovallo, McKey, & Pincomb, 1994; Ditto, 1986). A growing body of evidence suggests that hypoalgesia also precedes the onset of high blood pressure in humans and lab- oratory animals at risk for hypertension (al’Absi, Buchanan, & Lovallo, 1996; France, 1999; Page & France, 1997; Saavedra, 1981). For example, genetic strain rats that are predisposed for hypertension, but not yet hypertensives, show higher pain threshold relative to age-matched controls with similar blood pressure levels (Sitsen & Dejong, 1983). In human studies, normotensive individuals with positive parental history of hy- pertension report less pain in response to a variety of noxious stimuli than those with no parental history of high blood pressure (al’Absi et al., 1996; France, Adler, France, & Ditto, 1994). The extent to which baroreceptor activation contributes to attenuated pain sensitivity observed in individuals with positive parental history of hypertension has yet to be established. Clinical observations and experimental studies have demon- strated marked gender differences in pain perception, with This study was supported by a grant from National Institute of Health # HL64794. Address reprint requests to: Mustafa al’Absi, Ph.D., 1035 University Drive, 235 Medical School Building, University of Minnesota Medical School, Duluth, MN 55812, USA; e-mail: malabsi@umn.edu. Psychophysiology, 42 (2005), 83–91. Blackwell Publishing Inc. Printed in the USA. Copyright r 2005 Society for Psychophysiological Research DOI: 10.1111/j.1469-8986.2005.00257.x 83