Table 2

Increased HLa accumulation in the absence of O2-limitation

1. a.  HLa production depends on a competition for pyruvate and NADH between LDH and the NADH shuttles (malate-aspartate and glycerol-phosphate) and the pyruvate transporter (MCT)
 and/or
 b.  High activity of LDH and Keq of pyruvate to lactate reaction guarantees HLa production particularly with increasing glycolytic rate
2.  Phosphorylase is activated by increased work rate probably due to ↑ [Ca2+], ↑ [Pi], and ↑ [AMP]; this increases glycolytic rate ⇒ ↑ HLa production
3.  With increased exercise intensity; [ATP] ↓, [ADP] ↑, [AMP] ↑, [Pi] ↑, and [ammonia] ↑ ⇒ phosphofructokinase (PFK) activation and ↑ HLa production
4.  ↑ [Ca2+] may act in a feed-forward manner to activate phosphorylase and PFK independently of metabolic feedback
5.  Sympathoadrenal activity increases with work rate—epinephrine activates phosphorylase and thereby ↑ glycolysis and HLa production
6.  Sympathoadrenal activity also causes vasoconstriction and ↓ blood flow to liver, kidney, and inactive muscle ⇒ ↓ HLa oxidation and removal
7.  Fast twitch fiber recruitment increases HLa production
8.  HLa production exceeds removal ⇒ ↑ muscle and blood [HLa]
  • [Modified with permission from ref. 21 (Copyright 1996, Oxford University Press).]