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When starved for 48 h, rats appeared to have modified levels
of a protein
called pyruvate dehydrogenase kinase isoform 4, which
affects fat metabolism
in body muscles such that possibly insulin malfunction may
be averted. 48
rat hours should be many more human hours for fasting.
The paper below is free-full-text.

Holness MJ, Bulmer K, Gibbons GF, Sugden MC.
Up-regulation of pyruvate dehydrogenase kinase isoform 4
(PDK4) protein
expression in oxidative skeletal muscle does not require the
obligatory
participation of peroxisome-proliferator-activated receptor
alpha
(PPARalpha).

Biochem J. 2002 Sep 15;366(Pt 3):839-46.
PMID: 12099888

In insulin deficiency, increased lipid delivery and
oxidation suppress
skeletal-muscle glucose oxidation by inhibiting pyruvate
dehydrogenase
complex (PDC) activity via enhanced protein expression of
pyruvate
dehydrogenase kinase (PDK) isoform 4, which phosphorylates
(and inactivates)
PDC. Signalling via peroxisome-proliferator-activated
receptor alpha
(PPARalpha) is an important component of the mechanism
enhancing hepatic and
renal PDK4 protein expression. Activation of PPARalpha in
gastrocnemius, a
predominantly fast glycolytic (FG) muscle, also increases
PDK4 expression,
an effect that, if extended to all muscles, would be
predicted to
drastically restrict whole-body glucose disposal.
Paradoxically, chronic
activation of PPARalpha by WY14,643 treatment improves
glucose utilization
by muscles of insulin-resistant high-fat-fed rats. In the
resting state,
oxidative skeletal muscles are quantitatively more important
for glucose
disposal than FG muscles. We evaluated the participation of
PPARalpha in
regulating PDK4 protein expression in slow oxidative (SO)
skeletal muscle
(soleus) and fast oxidative-glycolytic (FOG) skeletal muscle
(anterior
tibialis) containing a high proportion of oxidative fibres.
In the fed
state, acute (24 h) activation of PPARalpha by WY14,643 in
vivo failed to
modify PDK4 protein expression in soleus, but modestly
enhanced PDK4 protein
expression in anterior tibialis. Starvation enhanced PDK4
protein expression
in both muscles, with the greater response in anterior
tibialis. WY14,643
treatment in vivo during starvation did not further enhance
upregulation of
PDK4 protein expression in either muscle type. Enhanced PDK4
protein
expression after starvation was retained in SO and FOG
skeletal muscles of
PPARalpha-deficient mice. Our data indicate that PDK4
protein expression in
oxidative skeletal muscle is regulated by a lipid-dependent
mechanism that
is not obligatorily dependent on signalling via PPARalpha.