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[A1CR]

Combining fasting with our CR is a strategy utilized among
some of our CR
group members. When we are short of calories, we may be
required to make
optimum utility of those calories that we obtain.
Optimizing the functions
of key enzymes that regulate the efficiency could be one
strategy that our
body employs to achieve efficiency. Previously, in the
full-text-free paper
(1), the authors of apparently the SJ Peters laboratory
group studied the
effect of what in humans would be a considerable time of
fasting the effect
on http://en.wikipedia.org/wiki/Allosteric
http://en.wikipedia.org/wiki/Pyruvate_dehydrogenase (PDK)
expression in its
different isoforms. Now, five years later, the same group
has examined the
amounts and allosteric
http://en.wikipedia.org/wiki/Pyruvate_dehydrogenase
activity (PDP) in the (2) paper. Thus, there may be a
coordination of the regulated expression levels of PDK and
PDP such that
sugars are maximally conserved for times of requirement
during fasting. Is
CR a relatively long-term form of fasting?

1. Peters SJ, Harris RA, Heigenhauser GJ, Spriet LL.
Muscle fiber type comparison of PDH kinase activity and
isoform expression
in fed and fasted rats.
Am J Physiol Regul Integr Comp Physiol. 2001 Mar;280(3):R661-8.
PMID: 11171643

Fiber type specificity for expression of all three rat
skeletal muscle
pyruvate dehydrogenase kinase (PDK) isoforms (PDK1, 2, and
4) was determined
in fed and 24-h fasted rats. PDK activity and isoform
protein and mRNA
contents were determined in white gastrocnemius (WG;
fast-twitch
glycolytic), red gastrocnemius (RG; fast-twitch oxidative),
and soleus (Sol;
slow-twitch oxidative) muscles. PDK activity was lower in WG
compared with
oxidative muscles (RG, Sol) in both fed and fasted rats. PDK
activities from
fed muscles were 0.12 +/- 0.04, 0.30 +/- 0.01, and 0.36 +/-
0.08 min(-1) in
WG, Sol, and RG, respectively, and increased in fasted
muscles (0.36 +/-
0.09, 0.68 +/- 0.18, and 0.80 +/- 0.14 min(-1)). This
correlated with
increased PDK4 protein and to a lesser extent with PDK4
mRNA. PDK2 protein
was not different between fiber types in fed or fasted rats,
but PDK2 mRNA
content was twofold greater in RG from fasted rats compared
with fed rats.
PDK1 was unaltered by fasting in all muscle types at both
the protein and
mRNA level, but in both fed and fasted rats had much greater
protein and
mRNA content in the oxidative vs. glycolytic muscles. In
conclusion, PDK
activity and PDK1 and 4 protein and mRNA were lower in
glycolytic vs.
oxidative muscles from fed and fasted rats. Fasting for 24 h
induced a two-
to threefold increase in PDK activity that was mainly due to
increases in
PDK4 protein and mRNA. PDK1 and 2 protein and mRNA were
generally unaltered
by fasting in all fiber types, except for increased PDK2
mRNA in the fast
oxidative fibers. Because the PDK isoforms vary greatly in
their kinetic
properties, their relative proportions in the three fiber
types at any given
time during fasting could significantly alter the acute
regulation of the
pyruvate dehydrogenase complex.

2. Leblanc PJ, Harris RA, Peters SJ.
Skeletal muscle fiber-type comparison of pyruvate
dehydrogenase phosphatase
activity and isoform expression in fed and food deprived rats.
Am J Physiol Endocrinol Metab. 2006 Oct 3; [Epub ahead of print]
PMID: 17018773


Fiber type specificity of pyruvate dehydrogenase
phosphatase was
determined in fed (CON) and 48 h food-deprived (FD) rats.
PDP activity and
isoform protein content were determined in soleus
(slow-twitch oxidative),
red gastrocnemius (RG; fast-twitch oxidative glycolytic),
and white
gastrocnemius (WG; fast-twitch glycolytic) muscles. When
normalized for
mitochondrial volume, there was no difference in PDP
activity between muscle
types or CON and FD. When expressed per gram wet tissue
weight, PDP activity
was higher in RG compared with soleus and WG in both CON and
FD rats. PDP
activities from CON muscles were 1.48 +/- 0.19, 2.68 +/-
0.65, and 1.20 +/-
0.33 nmol.min(-1).g wet weight tissue(-1) in soleus, RG, and
WG,
respectively, and decreased in FD muscles (1.22 +/- 0.22,
2.00 +/- 0.57, and
0.84 +/- 0.18 nmol.min(-1).g wet weight tissue(-1)). This
correlated with
increased PDP2 protein, however only in RG as PDP2 was not
detectable in
soleus or WG. PDP1 protein was not responsive to food
deprivation in all
fiber types. In conclusion, PDP activity and protein content
were higher in
fast-twitch oxidative glycolytic muscles from CON and FD
rats, identifying a
unique inter- and intra-muscular distribution. FD induced a
small but
significant decrease in PDP activity that was partially due
to decreases in
PDP2 protein. As a result, coordinate changes to PDP
activity opposite to
those of the other regulatory enzyme, pyruvate dehydrogenase
kinase, during
food deprivation would maximize the inactivation of skeletal
muscle pyruvate
dehydrogenase and enhance carbohydrate conservation during
periods of
limited carbohydrate supply.
... fed standard rat chow (27% protein, 11% fat, 63%
carbohydrate; 5012
Rat Diet ...) ad libitum until food withdrawal. ...
... Results
Mitochondrial preparation and CS activities
Mitochondrial recoveries were similar between
treatment groups for Sol
(CON, 14±5%; FD, 19±4%), RG (CON, 18±4%; FD, 16±2%), and WG
(CON, 9±3%; FD,
10±2%) and were similar between fiber types. Mitochondrial
quality was also
similar between treatment groups for Sol (CON, 69±6%; FD,
76±4%), RG (CON,
67±3%; FD, 68±7%), and WG (CON, 60±8%; FD, 60±4%) and were
similar between
fiber types.
There were no significant differences between whole
muscle homogenate
CS activities between treatment groups for Sol (CON,
22.2±1.7; FD, 22.0±2.2
?mol/min/g wet tissue wt-1), RG (CON, 27.0±1.2; FD, 28.3±2.0
?mol/min/g wet
tissue wt-1),and WG (CON, 12.6±1.2; FD, 15.1±4.0 ?mol/min/g
wet tissue
wt-1), with Sol CS activity being significantly lower than
RG but
significantly higher than WG.
Blood
ß-HB and FFA were significantly elevated and insulin
was significantly
lower after 48 hrs of food deprivation (Table 1). Glucose
levels remained
unchanged.

Table 1. Plasma insulin and FFA concentrations and whole
blood ß-HB and
glucose concentrations in fed and food-deprived rats.
=================================
CON FD
=================================
Insulin (mIU/L) 31.8±2.5 12.8±3.1*
FFA (mM) 0.11±0.01 0.35±0.07*
ß-HB (mM) 0.36±0.03 1.51±0.38*
Glucose (mM) 5.81±0.53 4.79±0.45
=================================
Values are means±SE for samples obtained from 6 animals
in each group.
CON, control; FD, food deprived; ß-HB,
ß-hydroxybutyrate; FFA, free fatty
acid.
*denotes significance from CON.

PDH and PDP activity
Food deprivation significantly decreased PDHa activity in
all skeletal
muscle fiber types (Table 2). PDP activities, expressed per
mg extracted
mitochondrial protein or g wet tissue weight, were
significantly lower (main
effect) in FD animals compared to CON, irrespective of
skeletal muscle type
(Table 3; Fig 1). PDP activities per g wet tissue weight
were significantly
higher (main effect) in RG compared to Sol and WG,
irrespective of treatment
(Fig 1).

Table 2. Pyruvate dehydrogenase (PDHa) activity for the
three skeletal
muscle types in fed and food-deprived rats.
========================================
Soleus RG WG
========================================
CON 0.36±0.14 0.64±0.13 0.41±0.05
FD nd 0.03±0.01* 0.14±0.04*
========================================
Values are means±SE in ?mol/min/g wet wt/tissue for
tissue samples
obtained from 5 animals in each group.
CON, control; FD, food deprived; RG, red gastrocnemius;
WG, white
gastrocnemius; nd, not detectable.
*denotes significance from CON.

Table 3. Pyruvate dehydrogenase phosphatase (PDP) activity
per mg of
extracted mitochondrial protein for the three skeletal
muscle types in fed
and food-deprived rats.
=======================================
Soleus RG WG
=======================================
CON 0.50±0.09 0.66±0.16 0.58±0.20
FD^§ 0.44±0.11 0.57±0.15 0.51±0.09
=======================================
Values are means±SE in nmol·min-1·mg extracted
mitochondrial protein-1
for tissue samples obtained from 8-10 animals in each group.
CON, control; FD, food deprived; RG, red gastrocnemius;
WG, white
gastrocnemius.
^§ a two-way ANOVA revealed a significant main effect
for treatment
(p<0.05).

PDP isoform protein
There was significantly more PDP1 protein in RG
compared to Sol and WG
(Fig 2). There was no effect of food-deprivation on PDP1
protein in any of
the skeletal muscle fiber types. PDP2 protein was not
detectable in Sol and
WG (Fig 3). Fooddeprivation significantly decreased PDP2
protein in RG.
... In summary, the present study clearly demonstrates
that PDP
activity is highest in a representative fast-twitch
oxidative glycolytic
muscle compared with both slow-twitch oxidative and
fast-twitch glycolytic
muscles. There is a unique inter- and intra-muscular
distribution of PDP
isoforms, with PDP1 protein highest in predominantly type
IIA muscle
compared with both type I and IIB muscles and PDP2 protein
detected
exclusively in predominantly type IIA muscles. In response
to 48 hrs food
deprivation, PDP activity decreased in all muscle types,
PDP2 decreased in
fast-twitch oxidative glycolytic muscle, and PDP1 was
unaltered. As a
result, coordinate changes to PDP activity opposite to those
of PDK activity
during food deprivation would maximize the inactivation of
skeletal muscle
PDH and enhance carbohydrate conservation during periods of
limited
carbohydrate supply.