Effects of Physical Activity on the Stress-induced Rise in C-Reactive Protein in Female Rats

by Kirksey, Susan Lee

Objective – Determine if acute psychosocial stress increases CRP; if increased voluntary physical activity decreases the rise in CRP caused by the stressor; if plasma norepinephrine (NE), corticosterone (CORT), interleukin-6 (IL-6) are physiological mediators underlying the stress-induced rise in CRP; and if blocking the estrogen receptor with tamoxifen (TAM) increases the rise in CRP caused by the stressor. Methods – Experiment 1: 36 WKY female rats, age 3.5-4 months, randomly divided into Control (C) = no treatment; Low Activity (LA) received Colony Stress (CS) and receptor antagonist treatments; and High Activity (HA)received 24/7 access to wheel, CS and receptor antagonist treatments. After HA animals had been running for 5 weeks, LA and HA were subjected to CS, then CS along with the following receptor antagonists, at two week intervals: alpha-adrenergic receptor antagonist, beta-adrenergic receptor antagonist, and CORT receptor antagonist. Six hours following each CS/Receptor antagonist treatment, blood samples were taken and plasma NE, IL-6, CORT, and CRP were measured. Experiment 2: 24 WKY female rats were randomly divided into C (CS only), LA (CS and TAM implant), and HA (24/7 access to wheel, CS and TAM implant). LA and HA were implanted with TAM capsules after HA had been running for 5 weeks. Blood was obtained and assayed as in Exp1. Results – CS caused significant increase in CRP in both experiments. Experiment 1: blocking adrenergic receptors significantly increased NE above Stress Baseline; blocking CORT receptors significantly increased CORT and IL-6 above Stress Baseline; however, stress-induced rise in NE and CORT were significantly lower for HA than LA. Experiment 2: NE for HA did not increase from Baseline to the final CS, while NE did increase from Baseline to the final CS for C and LA. TAM prevented the stress-induced rise in CRP for LA and HA but not for C. Conclusion - Increasing physical activity helped to minimize the NE and CORT response to stress. Blocking the estrogen receptor with TAM helped to prevent the CRP response to stress, potentially minimizing the harmful effects of the stress and inflammatory responses.