The study, “Impact of Psychological Stress on Pain Perception in an Animal Model of Endometriosis,” was published in the journal Reproductive Sciences.
Women with endometriosis are frequently burdened with severe pain, representing a significant source of both physiological and psychological stress. In a previous study, authors reported using a rat model of endometriosis that showed stress could worsen endometriosis. But it was unknown if exposure to a psychological stressor can cause changes in the sensory nervous system’s response.
In this study, authors tested the impact of psychological stress in pain thresholds and several pain receptors using a female rat model of endometriosis. A second group of mice remained endometriosis-free. Rats with endometriosis were exposed to psychological stress — in this case, water avoidance — for seven consecutive days. Control groups included rats induced for endometriosis but not submitted to any stress, and normal mice without stress.
As indicators of anxiety, authors counted the number of fecal pellets (FPO) and serum corticosterone levels (corticosterone is a hormone secreted by the adrenal cortex, involved in the stress response) at each stress experiment, as well as in the control groups. Additionally, authors collected blood samples from the tail vein of the rats at specific time points: at day 1, 4, and 7 of the stress protocol, always immediately after exposure to stress.
The rats’ perception to pain was also determined by several tests. Expression of Mu opioid receptor, and neurokinin-1 receptor, among other molecules, was measured in the rats’ spinal cord.
Authors observed that the animals induced for endometriosis and subjected to the stress (water avoidance) exhibited significant higher levels of corticosterone and had increased FPO output when compared to controls. Additionally, endometriosis-stressed animals showed increased signs of damage to the colon, higher infiltration of immune cells and endometriosis vesicles. No significant differences were found in the expression of the receptors between the experimental groups.
Both groups of rats with endometriosis developed hyperalgesia (abnormal heightened sensitivity to pain). Notably, stress appeared to reverse the abdominal pain caused by endometriosis.
Altogether, these results suggest that “animals subjected to stress develop more severe symptoms, but interestingly, stress seems to have beneficial effects on abdominal allodynia,” researchers concluded. This, the authors stated, “could be a consequence of the stress-induced analgesia phenomenon.”