Endurance training in early life results in long-term programming of heart mass in rats

We investigated the molecular pathways using microarray analysis to explain how endurance exercise in early life might be regulating the sustained increase in heart mass we have observed in these rats in adulthood. At 5 weeks of age, male WKY rats were allocated to one of the following exercise treatments: remained sedentary with post mortem (PM) at 9 or 24 weeks, early exercise training (from 5-9 weeks of age) with PM at 9 or 24 weeks, or later exercise training (from 20-24 weeks of age) with PM at 24 weeks (n=8 males/group). Exercise training involved treadmill running 5 days/ week for 4 weeks. Running duration progressively increased from 20 up to 60 minutes per day, with the treadmill speed set at 15 m/min for the first week and 20 m/min thereafter. At 9 or 24 weeks of age rats were killed with an intraperitoneal injection of Ilium Xylazil-20 (30 mg/kg) and Ketamine (225 mg/kg). The rats in the 9 week old early exercise and 24 week old later exercise groups were killed 72 hours following the last bout of treadmill running. Total RNA was obtained from the whole-hearts for analysis