Sex difference in plasma ammonia but not in muscle inosine monophosphate accumulation following sprint exercise in humans

Since accumulation of ammonia in plasma has been shown to be lower in femal es than in males following sprint exercise, we hypothesised that muscle ino sine monophosphate (IMP) accumulation would also be smaller in females, esp ecially in type II fibres. A relationship between plasma ammonia and muscle IMP accumulation was expected, since ammonia and TMP are formed in equimol ar amounts during the net breakdown of adenine nucleotides. The sprint-exer cise-induced IMP accumulation, measured in biopsies from vastus lateralis m uscle, did not differ between males (n = 16) and females (n = 16)either in type I fibres [males 4.6 (SD 3), females 5.7 (SD 2) mmol . kg(-1) dry muscl e], type II fibres [males 13.2(SD 4), females 12.6 (SD 3) mmol . kg(-1) dry muscle] or in mixed muscle [males 8.4 (SD 3), females 8.2 (SD 3) mmol . kg (-1) dry muscle]. The accumulation of plasma ammonia following the sprint w as 35% lower in the females than in the males. The inter-individual variati on in plasma ammonia accumulation was explained by the sex but not by the m uscle IMP accumulation as tested in a multiple regression analysis. In conc lusion, the smaller plasma ammonia accumulation following sprint exercise i n females than in males would seem not to be explained by a smaller muscle IMP accumulation per unit muscle during sprint exercise.