Metabolic responses to swimming exercise in Streptococcus pneumoniae infected rats

The present study was performed to determine whether alterations in fuel reserves or energy substrate utilization might explain the performance decrements that occur in bacterial infections. Male Fisher-Dunning rats were studied at 24, 48, and 72 h after inoculation with Streptococcus pneumoniae. Rats were either sedentary or subjected to a 2-h swimming session at these three time points (N = 10 in each group). A more than 60% reduction (P less than 0.01) in performance capacity was observed on day 3 of infection compared with that in noninfected controls. This infection in the rat is characterized by fever (P less than 0.01), depression of plasma zinc (P less than 0.01) and free fatty acid (FFA) levels (P less than 0.01), inhibition of the two- to threefold increase in fasting ketonemia, and a decreased (NS) insulin:glucagon ratio, indicating a catabolic state. Glycogen stores were reduced in the heart (47%), liver (43%), and skeletal muscles (39%) but not in the carcass. Superimposed exercise resulted in a further reduction but not depletion of liver, muscle, and carcass glycogen stores, a less pronounced lactic acid accumulation, and a lower oxygen debt. However, plasma FFA and ketone body levels were still maintained or even elevated, suggesting that fat is supplied as fuel during swimming exercise in this infection. Thus, results indicate that unavailability of energy substrates or lactacidosis is not limiting for performance capacity during this severe infection.