Biomedical subjects
Publications and source records attributed to D H Snow.
The ultrastructure of sweat glands from the skin of free sweating horses was compared with that of glands from anhidrotic cases. Evidence of atrophied and abnormal sweat glands in the anhidrotic horses indicates that the condition involves progressive failure of the glandular mechanism of sweat production.
The effect of physical training on the in vitro activities of key enzymes that provide quantitative information on the maximum capacities of anaerobic and aerobic metabolism has been investigated in the gluteal muscle of the horse. Training had no effect on the activities of 6-phosphofructokinase or creatine kinase, suggesting that there was no effect on the capacity of anaerobic metabolism in this muscle. However, the activities of hexokinase and citrate synthase were increased, indicating that training increased the capacity of aerobic metabolism. For comparative purposes, muscle fibre composition and enzyme activities were also determined in a group of foals and a group of broodmares.
Four thoroughbred horses performed 4 gallops (G1-G4) with intervals of 5 min. With one exception, gallops were sustained at maximal speed over 620 m. Muscle biopsy samples of the middle gluteal and brachiocephalicus were taken before, during, and after exercise and assayed for ATP and intermediary metabolites. The results showed a major involvement of the brachiocephalicus, in addition to the middle gluteal, during galloping. In three horses, who were clearly fatigued, muscle ATP decreased by up to 50% by the end of G4. This was matched by an equal rise in inosine 5'-monophosphate. Pronounced accumulations of glycerol 3-phosphate, glycerol, and lactate (up to 204 mmol X kg dry muscle-1) occurred with exercise. In the fourth horse, which was less fatigued, a decrease in ATP and increases in intermediary metabolites were much less. Postexercise there was little or no recovery in muscle ATP or lactate during 30 min. The decreases in ATP are consistent with a high activity of adenosine 5'-monophosphate deaminase in horse muscle and indicative also of the high level of anaerobic stress of the exercise program. There was evidence to suggest that the increase in muscle glycerol resulted from hydrolysis of glycerol 3-phosphate and not from the utilization of triglyceride.
The amino acid permeability of red blood cells from Equus caballus (thoroughbred, Arab, shire and pony), E przewalskii (Przewalski's horse), E asinus (donkey and mule) and E burchelli (common or plains zebra) was measured. Individual animals exhibited stable but widely differing rates of L-[U-14C]alanine uptake in the range 5 to 1554 mumol (litre cells)-1 h-1 (0.2 mM extracellular L-alanine, 37 degrees C). Of the thoroughbreds tested, 30 per cent had red blood cells which were essentially impermeable to L-alanine (5 to 10 mumol (litre cells)-1 h-1, giving transport rates similar to those found previously in amino acid transport-deficient sheep erythrocytes. In contrast, only 3 per cent of the ponies tested had red blood cells impermeable to L-alanine. No cases of erythrocyte amino acid transport deficiency were found in the other horse breeds and species tested.
The two major polypeptides H (Mr 49,000) and L (Mr 33,000) of equine sweat have been purified by gel filtration and characterised by gel electrophoresis and compositional analysis. Both H and L are glycoproteins containing sialic acid, neutral sugars, N-acetylglucosamine and N-acetylgalactosamine, but the two polypeptides differ considerably in the extent of glycosylation. H and L also differ in amino acid composition, but both contain only low levels of sulphur containing amino acids and histidine. These glycoproteins may behave as surfactants.
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The absorption characteristics of a new paste preparation of phenylbutazone were studied in ponies and thoroughbreds. The results suggested that at a similar dose rate of 5 mg/kg greater bioavailability results from the paste than from a powder preparation. Delivery of an accurate dosage of the paste was not possible using the multidose applicator. Repeated administration of the paste preparation (5 mg/kg twice daily) indicated that it is more toxic to both ponies and thoroughbreds than a powder preparation. In addition to the toxic manifestations previously reported, a neutropenia developed during administration. Repeated intravenous administration of phenylbutazone (3.3 mg/kg twice daily) for eight days produced no adverse effects.
1. The muscle composition of 3 breeds of rabbit was investigated histochemically in 3 muscle groups in order to identify whether heredity or environment was the predominant factor in dictating composition. 2. In the biceps femoris, differences between the breeds in myosin ATPase activity were due to heredity, whereas differences in oxidative potential were due to environment. 3. In the flexor digitorum longus, the wild rabbit possessed the highest percentage of type I fibres. This was environmentally induced.
The haematological response to racing and to fast and slow training exercise was investigated in studies involving two populations of horses which differed widely in geographical location, climatic factors and management (Newmarket and Hong Kong). The well documented elevations in erythrocyte parameters were demonstrated and changing responses in leucocyte parameters, resulting in variations in the neutrophil to lymphocyte (N/L) ratio were described. It was shown that the immediate response to the anticipation or stress of exercise was a decrease in N/L ratio in association with an increase in lymphocyte numbers. The magnitude of the lymphocyte increases was similar in the two populations of horses producing a reversal of the N/L ratio (lymphocytes predominating) in the British but not the Hong Kong horses, owing to the higher resting ratio of the latter population. At 3 and 4 h after exercise, an increase in N/L ratio occurred in association with an increase in neutrophils and decrease in lymphocytes. All parameters had returned to resting level by 6 h following exercise. Those and the many other factors associated with alterations in equine N/L ratios are discussed in terms of the need for care when interpreting the results of haematological examinations.
Temporal changes in sweat composition were studied in 4 horses during epinephrine (adrenaline) infusion (0.13 to 0.31 micrograms/kg/min for 3 hours), heat exposure (41 C, [33 C wet bulb] for 5 to 6 hours), and exercise (16 to 18 km/hr for 58 to 80 km). Four ponies also were studied during heat exposure. Sweat produced by each of the stimuli was hypertonic for Na+, K+, and Cl-. These electrolyte concentrations remained constant during the central period of the experiments, with changes occurring near the beginning and toward the end. The Na+ was significantly higher and K+ significantly lower in epinephrine-induced sweat than in heat-induced sweat, and the pattern of change in sweat Na/K ratio varied among the 3 stimuli. The Ca2+ concentration decreased with time and was hypotonic after 15 minutes of epinephrine-induced sweating. Concentrations of Mg2+ and protein decreased exponentially with time. There was a high correlation between them, although the Mg2+ was not protein-bound. Sweat urea concentration was directly related to plasma urea concentration. When plasma glucose concentration became greater than 10 to 12 mmole/L during epinephrine infusion, glucose appeared in the sweat and its concentration rose to 8 to 12 mmole/L of sweat when plasma glucose was more than 20 mmole/L.
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The absorption of orally administered phenylbutazone (5 mg/kg) was studied in 10 thoroughbreds, eight ponies and four pony foals. Large variations in area under the curve (AUC) and peak plasma concentrations were found both within an animal and within groups of animals. Administration of phenylbutazone (5 mg/kg) following an overnight fast resulted in no difference among the three groups of animals with respect to AUC (0 to 24 hours), mean (+/- sd) values of which were 132 +/- 68, 107 +/- 48 and 98 +/- 6, respectively. Absorption characteristics of two oral phenylbutazone preparations (Equipalazone; Arnolds and Prodynam; Leo Laboratories) (5 mg/kg) given after an overnight fast were similar. Feeding before drug administration decreased AUC and peak plasma concentration and extended the range of the time taken to attain the latter. Repeated twice daily administration of phenylbutazone (5 mg/kg) resulted in more rapid absorption following the morning than the afternoon dose. Investigations with meclofenamic acid (4.4 mg/kg) also resulted in highest peak plasma concentrations and AUC following overnight fast. It was found that absorption was slower with intramuscular injections of phenylbutazone (2.5 mg/kg) than after oral administration in the fasted animal.
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To analyse the fibre type composition of adult dog skeletal muscle, enzyme histochemistry, immunohistochemistry for type I, IIA and IIB myosins, and peptide mapping of myosin heavy chains isolated from typed single according to the activity of the m-ATPase after acidic and alkaline preincubation proved to be rather difficult and was only consistently achieved after a very careful adjustment of the systems used. One of these sub-classes of type II fibres stained more strongly for m-ATPase activity after acidic and alkaline preincubation, was oxidative-glycolytic and showed a strong reaction with an anti-type IIA myosin. The other one, however, although showed a faint reaction with an anti-type IIB myosin. Peptide mapping of the myosin heavy chains of typed single fibres revealed two populations of heavy chains among the type II fibre group. Thus, in dog muscle, we are confronted with the presence of two main classes of type II fibres, both oxidative-glycolytic, but differing in the structure of their myosin heavy chains. In contrast to some reports in the literature, no classical type IIB fibres could be detected.
A radioimmunological method was used as a screening procedure to determine the period of detection or "clearance time", for the horse, of therapeutic doses of the synthetic anabolic steroid nandrolone phenylpropionate. Seven horses, either at rest or being exercised, were given a course of weekly intramuscular injections of the steroid. On the separate occasion, some of the horses were given a single intramuscular injection of the same compound. The weekly injections maintained a high plasma concentration of nandrolone and/or metabolites. The mean (+/- sd) period of detection in plasma of these compounds was 23 (+/- 2) days (range 21 to 25) in resting horses and 20 (+/- 6) days (range 14 to 27) in exercised animals. The mean period of detection in urine was 25 (+/- 7) days (range 16 to 32) and 25 (+/- 12) days (range 9 to 38) for resting and exercised horses, respectively. After a single intramuscular injection to resting horses, the mean periods of detection were 12(+/- 2) days (range 9 to 15) and 13 (+/- 2) days (range 11 to 16) in plasma and urine, respectively. In all experiments there was considerable individual variation in the time taken for the plasma and urine concentrations to return to pre-dose values. This variation was particularly marked in the urine of exercised horses given a course of injections. With horses in training, this period may be over 5 weeks, a period approaching the minimum of 42 days advocated by the Royal College of Veterinary Surgeons that the therapeutic use of anabolic steroids should be discontinued before racing.
The effects of 7 weekly injections of the anabolic steroid nandrolone phenylpropionate (400 mg) were investigated in 4 healthy, mature geldings. Measurement of body weight, nitrogen retention and plasma urea failed to demonstrate a consistent anabolic effects. Examination of biopsies from the semitendinosus and biceps femoris muscles showed no alteration in water content or glycogen concentration with treatment. Similarly no changes were found in the activities of 6 muscle enzymes. However, a significant increase in the proportion of fast twitch low oxidative fibres of the biceps femoris was observed. The effects of the treatment on a wide range of plasma biochemical constituents were investigated. The occurrence of some components of stallion behaviour in the geldings was taken to reflect a residual androgenic activity in the compound.
The effect of 11 weekly injections of nandrolone phenylpropionate (400 mg) was investigated by a crossover trial (2 training periods) in 6 Thoroughbred geldings undergoing training. A decrease in body weight and flank measurement occurred only during the first training period and was not modified by the anabolic steroid. Urinary nitrogen excretion was lower in the anabolic treated animals only in the first training period. Neither training nor training plus nandrolone phenylpropionate administration caused any marked alteration in blood biochemistry or haematology. A significant decrease in plasma chloride and increase in haematocrit occurred independent of treatment in the latter, more extensive anaerobic training of both parts of the crossover. No change in urinary pH or specific gravity was found throughout the study. No evidence of improved racing performance due to nandrolone phenylpropionate administration was observed. Behavioural changes attributed to the drug could be detected for at least 6 weeks after the cessation of treatment.
The effect of 11 weekly injections of nandrolone phenylpropionate (400 mg) on some skeletal muscle parameters was investigated in 6 Thoroughbred geldings undergoing training. Three muscles were sampled, the middle gluteal, the biceps femoris and the semitendinosus. Training alone produced increases in the percentage of fast twitch high oxidative fibres (FTH), glycogen content and the activities of citrate synthase, 3-hydroxyacl CoA dehydrogenase and cytochrome oxidase. In contrast the training programme did not alter water content, total protein content, the activities of lactate dehydrogenase, phosphofructokinase of beta glucuronidase, fibre area ratios or the number of capillaries per unit fibre area. Nandrolone phenylpropionate given in conjunction with the training programme only resulted in changes in 2 of these parameters. There was no increase in the percentage of FTH fibres in the biceps femoris with anaerobic training and the fibre area ratio increased significantly in this muscle.