Biomedical subjects
D R Hodgson
Publications and source records attributed to D R Hodgson.
Cardiorespiratory responses to exercise in horses with different grades of idiopathic laryngeal hemiplegia.
The relationship between different grades of laryngeal function, as assessed by endoscopy at rest, and the measurements of indices of gas exchange and exercise capacity was assessed during a standardised treadmill exercise test in 149 horses. Horses with abnormalities other than idiopathic laryngeal hemiplegia (ILH) were excluded from the study and laryngeal function was graded according to an established system. There were no significant differences in age, weight, maximum oxygen uptake, maximum carbon dioxide production, maximum respiratory exchange ratio, maximum oxygen pulse and run time between the grades. Blood lactate concentration at 10 m/s was greater (P < 0.01) in horses with grade 5 laryngeal function than other grades. Minimum PaO2 (P < 0.001) and SaO2 (P < 0.01) were lower and maximum PaCO2 (P < 0.001), higher in horses with grades 4 and 5 laryngeal function than other grades. Horses with grade 4 function had a lower minimum CaO2 (P < 0.01) than horses with other grades. Minimum PAO2 decreased from grades 1 and 2 to grades 4 and 5 (P < 0.05). The minimum alveolar ventilation was lower (P < 0.05) in horses with grades 4 and 5 laryngeal function compared to other grades. The results of this study indicate that endoscopic assessment of laryngeal function at rest, using a simple grading system, provides an indication of dynamic changes in ventilation and the effects on blood gases during exercise. From the data, we suggest that horses that have some movement of the left arytenoid cartilage but are unable to achieve full abduction have similar ventilatory effects and blood gas responses during maximal exercise to those with complete paralysis. Some horses with grade 3 laryngeal function had blood gas results similar to those of horses with grades 4 and 5 laryngeal function, indicating that discrepancies may occur between the resting assessment and laryngeal function during strenuous exercise.
Effects of training on the development of exercise-induced arterial hypoxemia in horses.
OBJECTIVES: To compare the development of exercise-induced arterial hypoxemia in horses before and after training, and to determine whether increases in maximum oxygen uptake (VO2max) following training results in a greater degree of exercise-induced arterial hypoxemia. ANIMALS: 13 three- to five-year-old. Standardbred geldings without clinical signs of respiratory or cardiovascular disorders. PROCEDURE: Horses were rested for 4 months prior to commencing a 16-week training program. Arterial blood was collected from the transverse facial artery during standardized exercise tests performed before and after 8 and 16 weeks of training. Variables measured during exercise tests included arterial blood gas tensions and VO2max. Training and testing was performed on a treadmill set at a 10% slope. RESULTS: Minimum arterial partial pressures of oxygen (PaO2) during exercise decreased from 83.3 +/- 1.5 mm of Hg before training to 77.8 +/- 1.0 mm of Hg after 16 weeks of training. Maximum arterial oxygen content increased from 239.2 +/- 3.1 to 257.9 +/- 3.8 ml/L, which resulted from an increase in hemoglobin concentration. The VO2max increased by 19% following training. Minimum values of PaO2 and arterial oxygen saturation were significantly correlated with VO2max when data from each stage of training were pooled. Calculated values for minimum alveolar oxygen tension decreased after 8 weeks of training, and alveolar ventilation increased at the end of training. Alveolar-arterial oxygen tension of difference increased by 4 mm of Hg following training. CONCLUSIONS: In trained horses, an increase in VO2max is associated with a decrease in minimum PaO2, during intense exercise and is mostly attributable to an increase in the alveolar-arterial oxygen tension difference. Therefore, interpretation of blood gas data from exercising horses should take into consideration VO2max.
Involvement of phenylalanine 23 in the binding of IGF-1 to the insulin and type I IGF receptor.
The hydrophobic residue Phe-23 lies on a surface of insulin like growth factor 1 (IGF-1) which may be involved in binding to the type I IGF and insulin receptors. The possibility that Phe-23 participates directly in binding to these receptors has been investigated by comparing the properties of [F23G]IGF-1, a mutant of insulin-like growth factor 1 in which Phe-23 has been replaced by Gly, with those of IGF-1 and insulin. [F23G]IGF-1 has a 48-fold lower affinity for the type I IGF receptor, a markedly reduced affinity for the insulin receptor and a 100-fold reduced affinity for insulin-like growth factor binding proteins (IGFBPs) compared to IGF-1. [F23G]IGF-1 is a full IGF-1 agonist as measured by its ability to stimulate cell proliferation. Its potency was only 4.5-fold less than IGF-1, probably because its bioavailability was increased as a result of its reduced affinity for IGFBPs. The large reduction in the affinity of [F23G]IGF-1 for the type I IGF receptor and insulin receptor contrasts with the lack of effect of the corresponding alteration to insulin [FB24G]. Phe-B24 is not thought to be involved directly in the binding of insulin to the insulin receptor and the C-terminus of the B-chain of insulin is suggested to be displaced on binding. We suggest that for IGF-1, the C-terminus of the B chain cannot be displaced because of the presence of the C-domain and the large reduction in the binding affinities of [F23G]IGF-1 suggest that the Phe-23 side chain may be directly involved in binding of IGF-1 to the type I IGF and insulin receptors.
Cryptococcal meningitis in an alpaca.
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Surgical management of osteomyelitis of the sustentaculum tali in a horse.
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Equine neonatal septicaemia: 24 cases.
Equine neonatal septicaemia was confirmed in 24 foals hospitalised at the Rural Veterinary Centre between 1989 and 1992 with suspected septicaemia. Septicaemia was confirmed by culture of bacteria from blood of live foals and tissues obtained at necropsy of foals that died or were euthanased. Pathogenic bacteria isolated were predominantly Enterobacteriaceae (including Escherichia coli and Salmonella serovars) and Actinobacillus equuli. Clinical manifestations of septicaemia included signs of depression, dehydration, abnormalities in body temperature and manifestations of localised infection including diarrhoea, pneumonia, and septic arthritis. Most common haematological abnormalities were neutropenia and increase of circulating band neutrophils. Survival rate of foals with confirmed septicaemia was 70.8%. Survival was found to be less likely in the presence of pneumonia, severe signs of depression, marked haematological changes or septic arthritis at the time of admission. Seven foals were confirmed to have septic arthritis without concurrent septicaemia. Of these, 4 had multiple joint involvement. Bacteria isolated from infected joints were predominantly Salmonella serovars. Four foals with septic arthritis failed to survive, due to multiple joint infection, which was unresponsive to treatment. The clinical and haematological abnormalities present in foals with confirmed septicaemia and septic arthritis were consistent with those observed in other studies. The bacterial isolates from foals with confirmed septicaemia were similar to those isolated in other studies. In contrast, the bacteria isolated from foals with septic arthritis without concurrent septicaemia were different from other studies.
Traumatic rupture of the urinary bladder in a horse.
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Efficacy of metoclopramide for treatment of ileus in horses following small intestinal surgery: 70 cases (1989-1992).
In this retrospective study, postoperative ileus was studied in horses having resection of the small intestine followed by a jejunojejunal (n = 35) or a jejunocaecal (n = 35) anastomosis. Twenty-six horses received no metoclopramide, 27 received metoclopramide as an intermittent intravenous infusion and 17 horses received metoclopramide as a continuous intravenous infusion (0.04 mg/kg/hour). Horses receiving a continuous infusion of metoclopramide had a reduced total volume (P < 0.001), shorter duration (P < 0.001), and a slower rate (P < 0.001) of postoperative gastric reflux, and a shorter postoperative hospital stay (P < 0.01) when compared to horses receiving no metoclopramide and horses receiving metoclopramide as an intermittent infusion. Horses having jejunocaecostomy performed had a larger volume (P < 0.05), longer duration (P < 0.05), and a greater rate (P < 0.05) of postoperative gastric reflux, and a longer postoperative hospital stay (P < 0.001) than horses undergoing jejunojejunostomy. Horses that had an abdominal drain placed during surgery had a longer length of intestine resected (P < 0.05) and a longer postoperative hospital stay (P < 0.05) than horses without an abdominal drain. Horses that died or were euthanased during the postoperative period had a greater total volume (P < 0.05), longer duration (P < 0.05), and greater rate of postoperative gastric reflux (P < 0.01), a longer length of small intestine resected (P < 0.01), and a shorter postoperative hospital stay (P < 0.05) than horses that survived until discharge from the hospital. In a multivariate regression analysis the continuous infusion of metoclopramide was the only variable that contributed significantly to predicting the total volume (P < 0.001; r2 = 0.24), duration (P < 0.001; r2 = 0.24) and rate (P < 0.001; r2 = 0.25) of postoperative gastric reflux. We concluded that metoclopramide given as a continuous intravenous infusion decreased the incidence and severity of ileus following small intestinal resection and anastomosis in horses.
Polioencephalomalacia in two alpacas.
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Surgical correction of anorectal atresia and rectovaginal fistula in an alpaca cria.
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Effect of a warm-up on energy supply during high intensity exercise in horses.
The VO2(max) in racehorses is approximately double that of elite human athletes and the rate of increase in VO2 at the onset of high intensity exercise is much greater than in man. The kinetics of gas exchange are affected by a warm-up prior to exercise in humans, there being a greater aerobic contribution to high intensity exercise after warm-up. Our hypothesis was that a warm-up would increase aerobic energy delivery in racehorses during high intensity exercise. Thirteen fit Standardbred racehorses ran to fatigue at 115% of VO2(max) on a treadmill at 10% slope. Prior to acceleration, horses were exercised either for 5 min at 50% VO2(max) followed by 5 min walk, or walked for 2 min. Samples of expired gas were collected every 10 s during the run for determination of VO2 and VCO2 and measurement of maximal accumulated oxygen deficit (MAOD). Blood lactate concentration was measured 5 min post exercise. We found that with a warm-up, horses had faster kinetics of gas exchange and a greater proportion of their total energy requirement was supplied by aerobic sources. The aerobic contribution to total energy requirement with and without warm-up was, respectively, 79.3 +/- 1.0% and 72.4 +/- 1.7% (P < 0.01). There was also a higher MAOD (P < 0.01) in horses that had not been given a warm-up (mean +/- s.e.m. 34.7 +/- 2.6 and 47.3 +/- 2.6 mLO2eq/kg bwt with and without a warm-up respectively). However, there were no significant differences in total run time or estimated total energy expenditure between the 2 protocols. We concluded that during high intensity exercise to fatigue lasting 1 to 2 min, more than 70% of energy supply is from aerobic energy sources and that this contribution is even greater when the horses have received a warm-up.
Blood lactate: does Accusport equal accuracy?
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Redistribution of cardiac output in response to heat exposure in the pony.
Radioactive microspheres were used to measure cardiac output and blood flow to most major tissues in 4 ponies at rest in thermoneutral (16 degrees C/60% RH) and mildly hot (41 degrees C/34% RH) environments. In response to heat stress there were increases in cardiac output (2-fold), respiratory frequency (5-fold), blood flow to the skin of the body (3-fold), and limbs (50%), respiratory muscles (2-fold) and the upper respiratory tract (3-fold). Ponies were able to maintain body temperature in the hot environment by increasing blood flow to the tissues involved in heat dissipation, while blood flow to all other tissues remained stable. This was achieved by increasing the cardiac output without need for reduction of blood flow to other tissues.
Changes in maximum oxygen uptake during prolonged training, overtraining, and detraining in horses.
Thirteen standardbred horses were trained as follows: phase 1 (endurance training, 7 wk), phase 2 (high-intensity training, 9 wk), phase 3 (overload training, 18 wk), and phase 4 (detraining, 12 wk). In phase 3, the horses were divided into two groups: overload training (OLT) and control (C). The OLT group exercised at greater intensities, frequencies, and durations than group C. Overtraining occurred after 31 wk of training and was defined as a significant decrease in treadmill run time in response to a standardized exercise test. In the OLT group, there was a significant decrease in body weight (P < 0.05). From pretraining values of 117 +/- 2 (SE) ml.kg-1.min-1, maximal O2 uptake (VO2max) increased by 15% at the end of phase 1, and when signs of overtraining were first seen in the OLT group, VO2max was 29% higher (151 +/- 2 ml.kg-1.min-1 in both C and OLT groups) than pretraining values. There was no significant reduction in VO2max until after 6 wk detraining when VO2max was 137 +/- 2 ml.kg-1.min-1. By 12 wk detraining, mean VO2max was 134 +/- 2 ml.kg-1.min-1, still 15% above pretraining values. When overtraining developed, VO2max was not different between C and OLT groups, but maximal values for CO2 production (147 vs. 159 ml.kg-1.min-1) and respiratory exchange ratio (1.04 vs. 1.11) were lower in the OLT group. Overtraining was not associated with a decrease in VO2max and, after prolonged training, decreases in VO2max occurred slowly during detraining.
Serum alpha-tocopherol, vitamin A, and blood selenium concentrations, and glutathione peroxidase activity in llamas fed alfalfa hay.
OBJECTIVES: To measure blood selenium concentration and glutathione peroxidase (GSH-Px) activity and serum concentrations of vitamin A and alpha-tocopherol, and to determine the correlation between blood selenium concentration and GSH-Px activity of llamas fed alfalfa hay. DESIGN: Mean (+/- SD) serum vitamin A and alpha-tocopherol concentrations, blood selenium concentrations, and GSH-Px activity were calculated from 9 sequential blood samples collected from llamas fed a diet of alfalfa hay. ANIMALS: 15 clinically normal llamas (8 males, 7 females) between 10 and 14 months of age. PROCEDURE: Llamas were fed alfalfa hay for 40 days prior to sample collection and then for the duration of the trial. Vitamin E, selenium, and concentrations of vitamin A precursors were measured in the hay. Blood samples were collected on days 0, 6, 7, 9, 13, 20, 42, 64, and 98. Blood selenium concentrations were measured, using an inductively coupled spectrometric method. Blood GSH-Px activity was measured with a spectrophotometer, using a modification of a previously described assay. Isocratic high-performance liquid chromatography with florescent detection was used to determine serum alpha-tocopherol and vitamin A concentrations. RESULTS: The alfalfa hay contained 0.2 mg/kg of selenium, 5 mg/kg of vitamin E, and 0.9 mg/kg of vitamin A precursors. The mean (+/- SD) blood selenium concentration and GSH-Px activity were 0.179 +/- 0.032 micrograms/ml and 25.76 +/- 6.53 mU NADPH oxidized/min/mg of Hb, respectively, with a correlation coefficient of 0.97. The mean (+/- SD) concentrations for serum alpha-tocopherol and vitamin A were 128.1 +/- 41.7 and 74.8 +/- 5.5 micrograms/dl, respectively. CONCLUSIONS: Blood selenium concentrations in llamas are highly correlated to GSH-Px activity. Blood selenium concentrations in llamas appear to be similar to other domestic ruminants and diets containing 0.2 mg/kg of selenium appear to provide an adequate dietary source. The concentrations of vitamin A precursors and vitamin E in the hay were below currently recommended dietary levels for llamas, and alfalfa hay appears to provide an unreliable source of vitamins A and E in this species. Further studies are required to determine optimal dietary concentrations and to substantiate a reference range for these vitamins in llamas.
Mutations at positions 11 and 60 of insulin-like growth factor 1 reveal differences between its interactions with the type I insulin-like-growth-factor receptor and the insulin receptor.
Insulin-like growth factor 1 (IGF-1) and three analogues ([V11I]IGF-1, [V11T]IGF-1, and [Y60F]IGF-1), constructed by site-directed mutagenesis, were expressed as fusion proteins and secreted into the periplasmic space of Escherichia coli. Purified IGF were obtained following IgG Sepharose affinity and cation-exchange chromatographies of the products of hydroxylamine cleavage of fusion proteins. The properties of the mutants were assessed using (a) quantification of affinities for the human insulin receptor overexpressed on NIH 3T3 cells, (b) quantification of affinities for the type I IGF receptor via competition for binding to a monolayer of MDA-MB-231 cells, (c) promotion of the in vitro mitogenesis of growth-arrested MCF-7 cells in the presence of 17-beta-oestradiol, and (d) a competition assay for binding to IGF-binding proteins secreted by MCF-7 cells. The mutants exhibited decreases in affinity for the insulin receptor, relative to IGF-1, of 2.6-, 3.8- and, 8.8-fold for [Y60F]IGF-1, [V11I]IGF-1, and [V11T]IGF-1, respectively. IGF-1, [V11I]IGF-1, and [Y60F]IGF-1 were of equal potency in the growth assay and in affinity for the type I IGF receptor. [V11T]IGF-1 exhibited a three fold loss of potency in the type I IGF receptor-binding and growth assays. The mutants did not differ significantly from IGF-1 in their affinities for the IGF-binding proteins. The full-activity of [Y60F]IGF-1 at the type I IGF receptor, in contrast to the weakened receptor affinity of IGF-1 with a Leu substitution at this position, indicates a requirement for an aromatic ring, rather than a hydroxyl group, in the interaction of IGF-1 with the type I IGF receptor. The decrease in affinity for the insulin receptor of all the mutants indicates that, as in insulin, the residues Val11 and Tyr60 are important for the interaction of IGF-1 with the insulin receptor. The unchanged or minor changes in the affinities of the mutants for the type I IGF receptor contrast with the more deleterious effects of the mutations on insulin receptor binding and with the properties of analogues of insulin mutated at equivalent sites: 3-fold and 5-10-fold reductions in biological activity for [VB12I]insulin and [YA19F]insulin, respectively. Thus, the results obtained using the mutants indicate important differences between the IGF-1/type I IGF receptor and insulin/insulin receptor interactions.
Retropharyngeal lymph node infection in horses: 46 cases (1977-1992).
A retrospective study of 46 horses with retropharyngeal lymph node (RPLN) infection presented to the Rural Veterinary Centre between 1977 and 1992 was undertaken. Horses aged less than one year were most commonly represented (46%). Thirty-nine percent of cases had been exposed to horses with confirmed or suspected strangles (Streptococcus equi subsp equi infection) within the previous 8 weeks. Most frequent signs were unilateral or bilateral swelling of the throat region (65%), respiratory stertor/dyspnoea (35%), purulent nasal discharge (20%), inappetence and signs of depression (15%), and dysphagia (9%). All horses had a soft tissue density in the retropharyngeal region on radiographs. Rhinopharyngoscopy, ultrasonography, haematology as well as cytological and microbial analysis of material aspirated from the soft tissue swelling facilitated diagnosis in some horses. Fifteen horses (33%) were treated with procaine penicillin intramuscularly for 4 to 7 days followed by oral trimethoprim-sulphadimidine for 7 to 14 days. Non-steroidal anti-inflammatory drugs were administered to 6 horses. Four required tracheostomy for severe respiratory distress. The 15 horses treated medically responded to treatment and were discharged from hospital. Three horses (6%) with mild signs received no treatment and recovered uneventfully. Twenty-eight horses (61%) underwent general anaesthesia and surgical drainage of a RPLN abscess. Nineteen received procaine penicillin G for 4 to 7 days. Four of the nine horses that did not receive antibiotic treatment after surgery required further surgical drainage 10 days to 7 weeks after the initial surgery. Limited follow-up information was available for 37 horses.(ABSTRACT TRUNCATED AT 250 WORDS)