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

VIII. Disturbances of Gastrointestinal Function
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caused by a lack of pancreatic lipase, oleic acid absorption
will be normal, whereas that of triolein, which requires
lipolysis for absorption, will be significantly reduced.
The absorption of both compounds is reduced in intestinal
malabsorption.
5 . Vitamin A Absorption
The vitamin A absorption test measures intestinal lipid
absorption ( Hayden and Van Kruiningen, 1976 ). Normal
absorption of vitamin A requires secretion of bile and
pancreatic enzymes. After oral administration of 200,000
units of vitamin A in normal dogs, serum vitamin A concentrations
reach their peak at 6 to 8 h, with values ranging
between three and five times fasting serum levels. There
are small differences in vitamin A absorption between
breeds and delayed gastric emptying will also alter results.
6 . Other Tests for Assessment of Intestinal
Function
Simultaneous evaluation of pancreatic exocrine function
and intestinal absorptive function is used in dogs ( Rogers
et al., 1980 ; Stradley et al., 1979 ) and cats ( Hawkins,
et al., 1986 ; Sherding et al., 1982). The combined bentiromide
and D-xylose absorption tests have proved to be
useful diagnostically in dogs. Blood is normally taken at 0,
{ ½ } , 1, 1 { ½ } , 2, 2 { ½ } , and 3 h after oral administration of
the test solution but a single blood sample taken at 1 { ½ } h
was adequate for differential diagnostic purposes ( Stradley
et al., 1979 ). The combined bentiromide/D-xylose absorption
test was of limited usefulness in cats because of
marked individual variations. Peak blood PABA levels (60
to 120 min) and peak blood D-xylose levels (30 to 120 min)
in healthy cats were less than those of normal dogs, and
blood D-xylose levels in cats with infiltrative small bowel
disease were not abnormal ( Hawkins et al., 1986 ).
The content of exhaled hydrogen gas has been evaluated
as an indicator of carbohydrate malassimilation in
the dog ( Washabau et al., 1986 ), cat ( Muir et al., 1991 ),
calves ( Holland et al., 1986 ), and humans ( Perman, 1991 ).
Unabsorbed carbohydrate is fermented by bacteria in the
colon to H 2 and organic acids. Ten to 14% of the H 2 is
absorbed and excreted by the lungs ( Washabau et al., 1986 ).
Increases in pulmonary H 2 excretion can occur in normal
dogs fed rations containing wheat or corn flour. Increased
H 2 excretion normally occurs in most species receiving
lactulose. Mild increases in H 2 excretion occur in normal
humans and dogs receiving xylose but not in the cat.
Breath H 2 excretion has diagnostic value in determining
mouth-to-cecum transit time and for identifying small
intestinal bacterial overgrowth ( Muir et al., 1991 ). Falsenegative
H 2 breath tests have been seen in humans receiving
antibiotics. Diet as well as variations in bacterial flora
can also cause false-positive test results.
The nitrosonaphthol test qualitatively measures urinary
excretion of 4-hydroxyphenylacetic acid and related compounds,
which are intestinal bacterial degradation products
of tyrosine. The test has been used to differentiate pancreatic
or small intestinal diarrheal diseases from those associated
primarily with large bowel disease ( Burrows and
Jezyk, 1983 ). The test was positive in 77% of the dogs
with pancreatic and small intestinal disease and in only
9.5% of those dogs with large bowel disease. Positive tests
were associated with bacterial overgrowth of the small
intestine and became negative during antibiotic treatment
that resulted in clinical improvement. The test may be useful
in dogs to select patients with small intestinal bacterial
overgrowth, which might respond to antibiotic therapy.
G . Bacterial Overgrowth
The bacterial flora of the canine intestine increases in
number from the duodenum to colon. Factors maintaining
this aboral gradient are luminal patency, intestinal motility,
limited substrate availability, various bacteriostatic/cidal
secretions, and an intact ileocecocolic valve. Abnormalities
of these control mechanisms facilitate small intestinal bacterial
overgrowth (SIBO). SIBO is usually secondary to
another disease process, but it has been reported as a primary
idiopathic form. Many clinicians prefer to use the
term antibiotic-responsive diarrhea instead of idiopathic
SIBO ( German et al., 2003 ). Regardless, bacterial overgrowth
can interfere with the absorption of nutrients and
fluid by reducing microvillar enzyme activity, increasing
cellular or intercellular permeability, deconjugating bile
acids, and hydroxylating fatty acids.
A number of diseases ( Rutgers et al., 1988, 1993,
1995 ; Simpson et al ., 1990 ; Williams et al ., 1987 ) need to
be ruled out before making a diagnosis of idiopathic SIBO.
This includes exocrine pancreatic insufficiency (EPI), partial
or complete intestinal obstruction, intestinal stasis,
resection of the ileocecocolic valve, and intestinal mucosal
diseases that cause malabsorption (e.g., moderate to severe
inflammatory bowel disease), lymphoma, and lymphangiectasia.
Dogs and cats with partial intestinal obstruction
often have a history of chronic diarrhea and weight loss,
which responds to antibiotics ( Batt et al., 1988 ). Much of
the literature pertains to German shepherd dogs (GSD)
with subnormal levels of IgA ( Delles et al ., 1993, 1994 ;
Willard et al ., 1994a, 1994b ). SIBO has also been reported
in beagles with normal IgA levels ( Batt et al ., 1992 ).
In the dog, total bacterial counts exceeding 10 5 colonyforming
units per milliliter (cfu/ml) of proximal jejunal or
duodenal fluid and anaerobic bacterial counts exceeding
10 5 cfu/ml have been reported ( Burrows et al ., 1994 ).
Culture of duodenal juice has been regarded as the gold
standard for detecting bacterial counts 10 5 cfu/ml; this
assumption has been questioned because of the variability