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

Abstract

Since accumulation of ammonia in plasma has been shown to be lower in females than in males following sprint exercise, we hypothesised that muscle inosine monophosphate (IMP) accumulation would also be smaller in females, especially in type II fibres. A relationship between plasma ammonia and muscle IMP accumulation was expected, since ammonia and IMP are formed in equimolar amounts during the net breakdown of adenine nucleotides. The sprint-exercise-induced IMP accumulation, measured in biopsies from vastus lateralis muscle, 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 x kg(-1) dry muscle], type II fibres [males 13.2 (SD 4), females 12.6 (SD 4) mmol x kg(-1) dry muscle] or in mixed muscle [males 8.4 (SD 3), females 8.2 (SD 3) mmol x kg(-1) dry muscle]. The accumulation of plasma ammonia following the sprint was 35% lower in the females than in the males. The inter-individual variation in plasma ammonia accumulation was explained by the sex but not by the muscle IMP accumulation as tested in a multiple regression analysis. In conclusion, the smaller plasma ammonia accumulation following sprint exercise in females than in males would seem not to be explained by a smaller muscle IMP accumulation per unit muscle during sprint exercise.

Adipose tissue extracts plasma ammonia after sprint exercise in women and men

“…Certainly, in absolute terms, the NH 3 clearance by adipose tissue was of similar magnitude in women and men (see calculations above), but the clearance relative to body mass was greater in women (data not shown). As estimated earlier, the smaller muscle mass relative to body mass in the female group and thereby NH 3 production can account for 15-25% of the observed sex difference in plasma NH 3 after sprint exercise (10). Thus both greater clearance and smaller production of NH 3 relative to the body mass may contribute to the lower plasma NH 3 levels after sprint exercise in women compared with men.…”

“…To some extent, however, the sex difference in plasma NH 3 may depend on the smaller skeletal muscle mass (relative to body size) in women than in men. However, as estimated earlier, the difference in muscle mass can account for only 15-25% of the observed sex difference in plasma NH 3 after sprint exercise (10). This indicates the existence of an additional mechanism that would generate the observed sex difference.…”

Reduction in plasma leucine after sprint exercise is greater in males than in females

“…Thus, a larger net breakdown of ATP to IMP, in males in the exercising muscle may explain the gender difference in plasma ammonia after sprint exercise. However, the decrease in muscle ATP and the corresponding increase in IMP directly after one bout of sprint exercise did not differ between males and females when analyzed in pools of type I and type II fibers (Esbjornsson‐Liljedahl & Jansson, 1999). This may indicate that muscle ammonia production did not differ between males and females.…”

“…It is known from previous studies that there is a pronounced difference between males and females in the accumulation of ammonia in plasma after sprint exercise (Itoh & Ohkuwa, 1993; Nevill et al, 1996; Esbjornsson‐Liljedahl & Jansson, 1999; Esbjörnsson‐Liljedahl et al, 1999, 2002; Esbjörnsson et al, 2006, 2009).…”

“…However, gender difference in muscle fiber type proportions may still explain that muscle ammonia in “mixed tissue” differs between males and females after sprint exercise because less IMP is accumulated in type I than in type II fibers after sprint exercise. In addition, the accumulation of ammonia will be lower in type I than in type II muscle fibers (Esbjornsson‐Liljedahl & Jansson, 1999). An alternative explanation for the pronounced gender difference in plasma ammonia after sprint exercise has been raised and deals with the concept of buffering ammonia in the form of glutamine.…”