EXERCISE TRAINING BLUNTS SUPPRESSION OF SPLENIC NATURAL KILLER CELL CYTOLYSIS AFTER FOOTSHOCK 179

Abstract

We reported (J Appl Physiol, 78: 1547-1554, 1995) that 6 wk of circadian activity wheel running blocked the decrease in splenic Natural Killer Cell cytolysis induced by footshock, with no effects on baseline cytotoxicity. The study not determine whether an enriched environment or adaptations to exertion explained the results. The present study extended our test to exercise training. Male Fischer rats (60 d) were assigned randomly to: 1) a sedentary home-cage control group (n=8), 2) a sedentary treatment group (n=8), or 3) a treadmill exercise training group (n=8) (25 m/min, zero°, 45 min/d, 6 d/wk). After 6 wk, the treadmill and sedentary groups received uncontrollable footshock on 2 days separated by 24 h. Each day, 6 min of scrambled shock was delivered in bouts of 3-30 s, with a 30-s intershock period. Spleens and trunk blood were collected 30 min after shock on day 2. Cytotoxicity was determined by standard 4-h 51Cr release assay using YAC-1 target cells. B, CD8, CD4, THY1.1 and NK cell% were determined by flow cytometry. Plasma [levels] of[ACTH], [corticosterone], and [prolactin] were assayed by RIA. A group effect was found for effector:target ratio, F(2,21)=6.82 p=0.005. After footshock% lysis relative to HC controls was ≈ 40% for sedentary animals compared with≈ 80% for treadmill exercise trained animals. One-way ANOVA with Duncan post hoc tests indicated that [ACTH] and [corticosterone] were elevated after footshock compared with home-cage controls, p < 0.05, but did not differ by group. Groups did not differ on splenic cell percentages. Our results indicate that treadmill exercise training attenuates the suppression of splenic NK cytolysis induced by footshock. Thus, the apparently protective effect of chronic exercise on natural immunity in the Fischer male rat is not merely explainable by an enriched environment compared with standard husbandry.