Respuesta Al Dolor

Indian J Physiol Pharmacol 2010; 54(1) : 57-62

VARIATION IN RESPONSE TO EXPERIMENTAL PAIN ACROSS THE MENSTRUAL CYCLE IN WOMEN COMPARED WITH ONE MONTH RESPOSE IN MEN
MANOJ KUMAR 1 , JAGDISH NARAYAN, NAR SINGH VERMA 2 AND INDU SAXENA 3 Departments of 1 Physiology and 3 Biochemistry, SRMS Institute of Medical Sciences, and Bareilly – 243 202
2

Department of Physiology, CSM MedicalUniversity, Lucknow – 226 003

( Received on August 18, 2009 ) Abstract : Gender differences in pain perception have been reported in literature. However, most such studies have ignored the role of female sex hormones in influencing pain response across menstrual cycle (MC). In this study, we have investigated the variation in pain response on different days of the menstrual cycle. Ninety subjects (60females) were subjected to experimental pain of cold pressor task, on days 1, 7, 14, and 21 of the MC (females), and on four consecutive Mondays of a month (males). Male subjects showed no variation in pain response. Females reported higher pain sensitivity on days 7 and 14 of MC. We suggest that experimental pain studies involving female menstruating subjects should be carried out only during aparticular phase of the cycle, and this phase should be reported in literature to increase the reproducibility of the experiment. Key words : Cold pressor task menstrual cycle experimental pain pain response

INTRODUCTION Sex differences in the perception of noxious experimental stimuli have been reported by various groups, with women exhibiting higher pain sensitivity than men (1-3). Contradictoryreports, however, exist. Fillingim and Maixner (2) reviewed 34 human experimental studies and found sexrelated differences in only two-thirds of them. One factor that can explain the discrepancies observed is the variation of female hormone levels across the menstrual cycle. The authors have not specified the menstrual phase of female subjects at the time of conducting the experiment. Leutinizinghormone increases pain sensitivity in rats (4). Estradiol and progesterone have been stated to produce analgesia that is modulated through the
*Corresponding Author :

spinal cord k-opiate receptor analgesic system (5, 6). However, greater opioidmediated stress induced analgesia has been reported in male rats compared with female rats (7, 8); and estrogen is believed to cause this difference bysuppressing stress-induced analgesia (9). A typical menstrual cycle of 28 days can be divided into three phases. The follicular phase begins on the first day of menses and lasts 10-14 days. About 22-36 h before ovulation, a peak in estradiol level occurs, followed by a peak in leutinizing hormone level 10-12 h before ovulation. The phase after ovulation is called the luteal phase, which lasts for14 days. Progesterone peak and a secondary estradiol peak occur 8 days after ovulation, i.e. on the 18 th -22 nd day of the menstrual cycle. The levels of estrogen and progesterone in blood start falling rapidly 9-11 days after ovulation and reach

Dr. Manoj Kumar, Department of Physiology, Teerthanker Mahaveer Medical College and Research Centre, Theerthanker Mahaveer University, Bagarpur,Delhi Road (NH–24) Moradabad–244 001 (U.P.)

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Manoj Kumar et al

Indian J Physiol Pharmacol 2010; 54(1)

their lowest levels at menstrual period (10).

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On the basis of the above facts, pain s e n s i t i v i t y s h o u l d d e c r e a s e o n t h e 1 3 th d a y when estradiol peak appears, and after 17 th day when both estradiol and progesterone levels arehigh. Goolkasian (11) reviewed the literature and reported a consistent pattern of highest pain sensitivity during days 1522 of a 28-day cycle, contrary to what is expected. However, Hellstrom and Lundberg (12) have reported contradictory observations. They performed cold pressor task (CPT) on female subjects in two phases of the menstrual cycle, and found pain sensitivity to be significantly...