Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

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Chapter | 28 Avian Clinical Biochemistry
TABLE 28-1 Mean ( SD) t½β in Plasma of IV Injected Homologous Enzymes in the Racing Pigeon (n 6)
Source Enzyme t1/2β(hours) Regression Function SD of Slope r
Liver AST 7.66 1.55 log y 2.6 0.04 x 0.008 0.9711
ALT 15.69 1.70 log y 2.1 0.02 x 0.002 0.9455
LD 0.71 0.10 log y 3.5 0.44 x 0.065 0.9901
GLDH 0.68 0.17 log y 2.3 0.46 x 0.150 0.9964
Muscle AST 6.51 0.83 log y 2.7 0.05 x 0.007 0.9652
ALT 11.99 1.32 log y 2.7 0.03 x 0.003 0.9712
LD 0.48 0.07 log y 4.0 0.60 x 0.119 0.9882
CK 3.07 0.59 log y 3.7 0.10 x 0.019 0.9652
Reprinted with permission from Lumeij et al . (1988a) .
Plasma enzyme activity (IU/I)
10,000
5,000
1,000
500
100
50
10
5
1
CK (110-480 IU/I)
LD (30-205 IU/I)
ASAT (45-123 IU/I)
ALAT (19- 48 IU/I)
0 20 60 100 140 180 220
Time (hours)
FIGURE 28-16 Mean ( SEM) plasma enzyme activities after intramuscular
injection of 75 mg/kg doxycycline (Vibramycin
R
-Pfizer, New
York) in six racing pigeons. The parts of the curves that are above the
reference range are indicated with continuous lines. Variables that did not
show elevations above the reference range during the entire experiment
(GLDH, AP, and bile acids) are not indicated. On histological examination
at t 215 h, degeneration and necrosis of muscle cells was observed.
Reprinted with permission from Lumeij et al . (1988b) .
of liver cells and hepatitis with single-cell necrosis did
not give rise to elevated plasma GLDH activities. Plasma
CK activity was never increased because of liver damage,
whereas GLDH, GGT, and BA were never elevated during
muscle damage. Thus, these four constituents are useful for
differentiating between liver and muscle disease. GLDH
is the most liver-specific enzyme in the racing pigeon.
Because GLDH is localized within the mitochondria of the
liver cells, increased plasma GLDH activities, however, are
only observed after liver cell necrosis.
The enzymes that are the most specific indicators of
muscle and liver cell damage (CK and GLDH, respectively)
have shorter half-lives than AST and ALT, which are not
specific indicators of damage to either organ. Thus, after
muscle or liver cell damage, AST and ALT activities in
plasma can be increased, even though CK or GLDH activities
have returned to baseline values. The fact that LDH
has a shorter half-life than CK makes this enzyme valuable
for differentiating between muscle and liver disease
in the pigeon. When plasma LDH activity is increased in
the absence of elevated CK activity, muscle damage is
unlikely. Enzyme profiles can only serve as rough guides
to interpretation of elevated plasma enzyme activity and
are not characteristic for a particular organ. The most
important reason is that the enzyme profile alters after
enzymes have entered the circulation resulting from different
removal rates for the various components.
Based on the tissue enzyme studies, it seemed that
LD was the most sensitive indicator of liver cell damage,
whereas ALT, because of its low activity in liver, would
be of limited value. It also seemed that LDH would be
a more sensitive indicator of muscle cell damage than
ALT. Experimentally induced liver and muscle damage,
however, demonstrated that ALT activity in plasma is
increased sooner than LDH activity. The relative increase
of ALT was also larger than that of LDH, except in severe
liver cell damage accompanied by large areas of necrosis.
Plasma ALT activities were increased for a longer period
after organ damage compared to LDH. These findings can
be explained by differences between their clearance halflives.
The clearance half-life of LDH is 15 to 30 times less
than that of ALT.
Campbell (1986) reported increased AST and ALT
activities in 75% of pigeons with aflatoxin B1-induced
liver damage and increased LDH activities in 33%. In
addition, AP and GGT were not sensitive indicators of
liver disease in pigeons, cockatiels, red-tailed hawks, and
great horned owls. With the exception of GGT, these findings
were confirmed by Lumeij et al. (1988a, 1988b) .
The discrepancy might reflect the difference in the hepatotoxic
agents used. In the study of Lumeij et al. (1988a,
1988b) , GGT activities were increased in the majority of
pigeons with experimentally induced liver disease, though