Objective—To quantify dimensions of the small
intestine of dogs and describe changes in histologic
characteristics of the mucosa during postnatal development.
Sample Population—Gastrointestinal tract tissues
obtained from 110 Beagles (15 adult females and 95
puppies of both sexes).
Procedure—Several variables (length, total weight,
mucosal weight, and nominal surface area) of the
small intestine were measured in puppies at birth but
before suckling; 1 day after birth and subsequent
suckling, 21, 42, and 63 days after birth, and in the
adult dams of the puppies. Tissue structure was
examined and quantified at each time point by use of
routine histologic examination and ocular micrometry
of formalin-fixed specimens stained with H&E.
Results—Small intestinal dimensions increased
throughout development with the greatest proportional
changes during the first day after birth and
onset of suckling. Villus height decreased during suckling
but had consistent values from 42 days after birth
to maturity, whereas crypt depth increased from birth
to maturity. Vacuolated enterocytes were evident
from birth to 21 days but not thereafter.
Conclusions and Clinical Relevance—Increases in
intestinal dimensions provide growing dogs with a
greater capacity for digestion and absorption.
Changes in mucosal architecture and cell populations
coincided with shifts in dietary inputs. These findings
may assist in the diagnosis of small intestinal diseases
and nutritional responses during growth and
development of dogs. (Am J Vet Res 2003;64:618–626)
Objective—To determine distribution of urokinase plasminogen activator-like protein and urokinase plasminogen activator receptor-like protein in urinary tract tissues of healthy dogs.
Animals—11 healthy dogs.
Procedures—Necropsy specimens from kidney, ureter, bladder, urethra, prostate, and testis were obtained from 4 sexually intact female dogs, 5 sexually intact males, and 2 castrated males; dogs ranged in age from juvenile to adult. Urokinase plasminogen activator-like protein and urokinase plasminogen activator receptor-like protein in tissue lysates from kidney, prostate, and testis were identified by use of SDS-PAGE, western blot analysis, and immunoprecipitation. Urokinase plasminogen activator-like protein and urokinase plasminogen activator receptor-like protein in kidney, ureter, urinary bladder, urethra, prostate, and testis were identified by use of immunohistochemical staining of tissue sections.
Results—Urokinase plasminogen activator-like protein and urokinase plasminogen activator receptor-like protein in the molecular-weight range published for urokinase and urokinase receptor (53 and 33 kd for urokinase and 60 to 65 kd for urokinase receptor) were identified. Distribution of the proteins identified by use of immunohistochemical staining was comparable with published information for humans and mice for the urinary tract. Staining of these proteins was detected in more tissue types than reported in healthy humans.
Conclusions and Clinical Relevance—Urokinase plasminogen activator-like protein and urokinase plasminogen activator receptor-like protein were detected in the urinary tract of healthy dogs. This information is important for further evaluation of the functions of urokinase and urokinase receptor in the canine urinary tract and the pathophysiologic features of urinary tract disease.
Objective—To determine and compare the number,
type, location, and distribution of apoptotic epidermal
cells in the laminae of clinically normal horses and
horses with laminitis.
Sample Population—Formalin-fixed samples of digital
lamellar tissue from 47 horses (including clinically
normal horses [controls; n = 7], horses with acute 
and chronic  naturally acquired laminitis, and horses
with black walnut extract-induced  or carbohydrate
overload-induced  laminitis).
Procedure—Blocks of paraffin-embedded lamellar tissues
were stained for DNA fragmentation with the
terminal deoxynucleotidyl transferase-mediated dUTP
nick-end labeling (TUNEL) technique. Differential
immunohistochemical staining for caspases 3 and 14
were used to confirm apoptosis.
Results—The number of TUNEL-positive epidermal
cells per 0.1 mm of primary laminae was significantly
greater in the acute laminitis group than in the other
groups. In the acute laminitis group, there were 17
and 1,025 times as many TUNEL-positive basal layer
cells and keratinocytes, respectively, compared with
the control group. Apoptosis of TUNEL-positive basal
layer cells was confirmed by results of caspase 3
immunohistochemical staining. The TUNEL-positive
keratinocytes did not stain for caspases 3 or 14.
Conclusions and Clinical Relevance—The large
number of apoptotic basal layer cells detected in the
lamellar tissue of horses with acute naturally acquired
laminitis suggests that apoptosis may be important in
the development of acute laminitis. The role of the
large number of TUNEL-positive keratinocytes detected
in the interface of primary and secondary epidermal
laminae of horses with acute laminitis remains to
be elucidated. ( Am J Vet Res 2004;65:578–585)
Objective—To immunohistochemically determine the expression of endothelin (ET) receptors in bronchial smooth muscle and epithelium of healthy horses and horses affected by summer pasture-associated obstructive pulmonary disease (SPAOPD).
Sample Population—Tissue specimens obtained from 8 healthy and 8 SPAOPD-affected horses.
Procedure—Horses were examined and assigned to healthy and SPAOPD groups. Horses were then euthanatized, and tissue specimens containing bronchi of approximately 4 to 8 mm in diameter were immediately collected from all lung lobes, fixed in zinc-formalin solution for 12 hours, and embedded in paraffin. Polyclonal primary antibodies against ET-A or ET-B receptors at a dilution of 1:200 and biotinylated IgG secondary antibodies were applied to tissue sections, followed by the addition of an avidin-biotin immunoperoxidase complex. Photographs of the stained slides were digitally recorded and analyzed by use of image analysis software to determine the intensity of staining. Two-way ANOVA was used for statistical analysis.
Results—The left diaphragmatic lung lobe of SPAOPD-affected horses had a significantly greater area of bronchial smooth muscle that immunostained for ET-A, compared with that for healthy horses. All lung lobes of SPAOPD-affected horses, except for the right diaphragmatic lobe, had significantly greater staining for ET-B receptors in bronchial smooth muscle, compared with results for healthy horses.
Conclusions and Clinical Relevance—This study revealed overexpression of ET-A and, in particular, ETB receptors in the bronchial smooth muscle of SPAOPD-affected horses, which suggested upregulation of these receptors. These findings improve our understanding of the role of ET-1 in the pathogenesis of SPAOPD.
Objective—To determine the effects of clenbuterol, at a dosage of up to 3.2 μg/kg for 14 days, PO, on skeletal and cardiac muscle in healthy horses undergoing treadmill exercise.
Animals—12 healthy horses from 3 to 10 years old.
Procedures—Horses were randomly assigned to a control group (n = 6) or clenbuterol group (6) and received either saline (0.9% NaCl) solution or clenbuterol, PO, every 12 hours for 14 days. Horses were subjected to submaximal treadmill exercise daily during treatment. Muscle biopsy specimens were collected before and after treatment for determination of apoptosis. Echocardiographic measurements, serum clenbuterol and cardiac troponin I concentrations, and serum activities of creatine kinase and aspartate aminotransferase were measured before, during, and after treatment. Jugular venous blood samples were collected every 3 days during treatment. Echocardiography was repeated every 7 days after beginning treatment. Response variables were compared between treatment groups and across time periods.
Results—No significant effect of clenbuterol or exercise on response variables was found between treatment and control groups at any time point or within groups over time.
Conclusions and Clinical Relevance—Results did not reveal any adverse effects of treatment with an approved dose of clenbuterol on equine cardiac or skeletal muscle in the small number of horses tested.
Objective—To determine the feasibility of performing serial laminar and skin biopsies on sedated horses and whether sampling affected adjacent tissues.
Procedures—Laminar tissues were harvested via biopsy through the hoof wall from healthy conscious horses via sedation and regional anesthesia. Eight specimens were collected at 4 time points during 24 hours from a single foot. Laminar biopsy specimens were harvested with a 6-mm-diameter biopsy punch after burring through the horny corium to the stratum medium. Skin biopsy specimens were collected from an area proximal to the coronary band. All tissues were examined via light microscopy. Total RNA was extracted and quantified, and gene expression analysis was completed for 2 housekeeping genes and the inflammatory mediator cyclooxygenase-2.
Results—Laminar and skin biopsies yielded adequate specimens for histologic and gene expression evaluation. There was no extension of inflammation or detectable damage to adjacent tissues during the 24-hour period in either laminar or skin specimens as judged via histologic findings and cyclooxygenase-2 expression. Lameness and discomfort induced by the procedure were minimal.
Conclusions and Clinical Relevance—Laminar biopsy provided a satisfactory method of collecting laminar specimens and allowed serial sampling of individual horses.