Exercise in the Heat: Effects of Dinitrophenol Administration,

Although dinitrophenol DNP stimulates excessive heat production by uncoupling oxidative phosphorylation, its effects on performance and thermoregulation during exercise in the heat have not been assessed. DNP was administered in two equal dosages 20mgkg, 30 min interval the second injection was followed immediately by exercise 9.14mmin in the heat 30 C or at room temperature 21 C until exhaustion or 99 min. At 21 C control saline-treated rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals. Respective increments in Tre for both groups were 0.02 Cmin and 0.08 Cmin. At 30 C control rats ran for 65 min Tremin0.05 C while DNP-treated animals had a mean endurance of only 12 min Tremin-0.22 C. DNP-treated rats 30 C certainly manifested no decrement in tail-skin heat loss Tskmin0.17 C vs 0.10 C or saliva secretion 0.78gmin,DNP vs 0.19gmin, control for their brief treadmill duration. Heat stress and DNP prevented the normal reduction in hematocrit and plasma protein levels during exercise while DNP increased osmolality and potassium levels post-exercise.