Original Research Article DOI: 10.18231/2394-2126.2017.0124 Indian Journal of Clinical Anatomy and Physiology, October-December, 2017;4(4):498-503 498 Cardiovascular reactivity and pain perception to thermal noxious stimuli across different phases of Menstrual Cycle Nirmala S Anand 1,* , Shivaprasad S. Goudar 2 1 Assistant Professor, 2 Professor, Dept. of Physiology, JNMC, Belgaum *Corresponding Author: Email: drnirm79@gmail.com Abstract Epidemiological studies on animal and human participants have failed to reach a consensus regarding the interaction of the autonomic nervous system with the female gonadal hormones and this paucity in research is important for a number of reasons since an alarming number of females complain of chronic pain and cardiovascular diseases throughout their reproductive lifespan the results of this complex interaction will help unraveling strategies for planning as well as implementation.. The aim of the present study was to examine whether the different phases of menstrual cycle alter the cardiac functioning as well as the pain nociception tested using the Cold Pressor test. Thirty eumenorrhic females were recruited and examined during the follicular and luteal phases of menstrual cycle for changes in the heart rate, systolic and diastolic blood pressures as well as for pain threshold, tolerance and its perception during Cold Pressor test. The results from our study proved that the heart rate, systolic and diastolic blood pressures were higher while the pain threshold and tolerance was lower during the luteal phase. We hence conclude that the luteal phase induces a greater cardiovascular reactivity and pain nociception as a result of greater sympathetic arousal due to interaction of the Autonomic nervous system with the endogenous gonadal hormones. Keyword: Cold pressor test, Estrogen, Menstrual cycle, Vagal. Received: 21 st July, 2017 Accepted: 9 th September, 2017 Introduction Menstruation is a regular cyclical sloughing of the uterine lining due to the interactions of hormones produced by the hypothalamus, pituitary, and ovaries which function together as Hypothalamo -pituitary Axis. (1,2) The cyclical fluctuation in the plasma levels of gonadal steroids estrogen and progesterone underlie the physiology the menstrual cycle. Follicular phase is primarily a phase of increased estrogen levels while the luteal phase shows an increase in the levels of progesterone, these gonadal hormones are modulators of HPA(Hypothalamo-pituitary adrenal axis) axis, which along with ANS, form the stress system which regulates multiple homeostatic mechanisms regulating the cardiovascular system especially its cardiac reactivity. (3) Heart is an organ which is controlled by the autonomic nervous system and its functioning shows variations across the normal menstrual cycle which are consistent with established actions of female-sex hormones. (4,5) Certain studies conducted have used the heart rate variability as a marker of ANS fluctuation and proved a significantly higher sympathetic activity in the luteal phase (6,7) while another study proved that cyclic variations in endogenous sex hormone levels during the menstrual cycle were not significantly associated with changes in cardiac autonomic control. (8,9) It is speculated that the cyclical hormonal profile may affect the ANS with certain consequences on the cardiovascular functioning and is an important indicator of health, because adults with autonomic dysfunction have higher all-cause and cardiovascular mortality rates. (10,11,12) Despite that, the literature is not clear about the influence of this relation. There are documented non reproductive actions of endogenous sex steroids and its interaction with the pain processing and analgesic pathways is just one of them. Animal and human researches have demonstrated fluctuating pain sensitivities and variability in the central modulation of pain across the phases of menstrual cycle which can be attributed to gonadal steroid interactions both at the CNS as well as PNS levels. (13,14) Though it is well known that there is fluctuation in pain sensitivity across the cycle but its exact effect on responses experienced has not been studied. The 1994-95 National population health survey made certain subtle observations that women have higher subjective pain ratings in response to painful stimuli compared to their counterpart males (20 % vs 16%) and the intensity as well as frequency increase after the age of 15 years. (15,16) Literature on the interaction of endogenous gonadal hormones with the pain processing systems of the body will pose itself to controversies with some reporting higher pain thresholds at times of the menstrual cycle when the estrogen levels in the body are high since estrogen is involved in modulation of somatic sensory processes while others demonstrate reduced pain sensitivity during menstrual and premenstrual phases compared to mid-menstrual and ovulatory phases of menstrual cycle. (17,13,14)