Increased rat neonatal activity influences adult cytokine levels and relative muscle mass

Abstract

Little is known about the effect of physical activity in early life on subsequent growth and regulation of inflammation. We previously reported that exposure of muscles in growing rats to IL-6 results in decreased muscle growth apparently because of a state of resistance to growth factors such IGF-I and that running exercise could ameliorate this growth defect. Herein, we hypothesized that increased activity, for a brief period during neonatal life, would pattern the adult rat toward a less inflammatory phenotype. Neonatal rats were induced to move about their cage for brief periods from d 5 to d 15 postpartum. Additional groups were undisturbed controls (CONs) and handled (HAND). Subgroups of rats were sampled at the age of 30 and 65 d. Relative to CON and HAND groups, the neonatal exercise (EX) group demonstrated a decrease in circulating levels of TNFα, IL-6, and IL-1β in adulthood, primarily in male rats. In addition, adult male EX rats had lower body mass and increased skeletal muscle mass suggesting a leaner phenotype. The results of this study suggest that moderate increases in activity early in life can influence the adult toward a more healthy phenotype with regard to inflammatory mediators and relative muscle mass.

Figure 1. The effects of prior neonatal activity on selected circulating cytokines at post-partum day 30

Rat neonates experienced increased physical activity (EX), handling (HAND) or no treatment (CON) from post-partum day 5 through 15. A subgroup was sampled at day 30. The neonatal activity treatment resulted in lower circulating levels of TNFα and higher IL-6 in 30 day males. Plasma levels of IL-1β were elevated in HAND rats relative to CON and EX. n = 8; *, P<0.05 vs. CON; ‡, P<0.05 vs. HAND.

Figure 2. The effects of prior neonatal activity on selected circulating cytokines at post-partum day 65

Rat neonates experienced increased physical activity (EX), handling (HAND) or no treatment (CON) from post-partum day 5 through 15. A subgroup was sampled at day 65. In males, the neonatal activity treatment resulted in lower circulating levels of IL-6, TNFα and IL-1β at 60 days of age. Plasma levels of IL-6 were also lower in 65 day EX females. Both male and female HAND rats demonstrated IL-6 levels that were lower than CON. n = 8; *, P<0.05 vs. CON; ‡, P<0.05 vs. HAND.