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Biomedical subjects

S N Dixon

Publications and source records attributed to S N Dixon.

17 recordsLinked to original sources
PubMed1995

Distribution and elimination of clenbuterol in tissues and fluids of calves following prolonged oral administration at a growth-promoting dose.

A pharmacokinetic study is described in which Friesian calves (n = 30) were treated orally with clenbuterol at 10 times the therapeutic dose. The study was designed to establish the distribution and elimination of clenbuterol from edible tissues, the major compartments of the eye and body fluids. Animals (n = 24) were dosed (10 micrograms/kg body weight) twice daily with clenbuterol for 21 days and slaughtered in groups of five (one untreated control animal per group) at 6 h and 1, 2, 4, 8 and 16 days after cessation of treatment. At slaughter, samples of diaphragm muscle, liver, kidney, bile, urine and both eyes were obtained. One of the eyes was separated into constituent tissues: aqueous humour, vitreous humour, cornea, lens, retina (without pigmented epithelium), choroid (with pigmented retinal epithelium; choroid/PRE) and sclera. All samples were stored at -20 degrees C. Clenbuterol concentrations were higher in liver than kidney, bile and urine from day 2 of withdrawal onwards. Concentrations in choroid/PRE were at least 10 times higher than in liver at all periods following cessation of treatment and 52 times higher 16 days after treatment. The concentrations of clenbuterol in the constituent tissues of the eye were in the order choroid/PRE > cornea > > retina > aqueous humour/vitreous humour > or = lens. Concentrations of clenbuterol in choroid/PRE taken from eyes frozen whole were generally lower than those in choroid/PRE separated before storage. Choroid/PRE stored by either method contained clenbuterol at more than 100 ng/g 16 days following cessation of treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1986

Radioimmunoassay of the anabolic agent zeranol. III. Zeranol concentrations in the faeces of steers implanted with zeranol (Ralgro).

Using a monoclonal antibody raised against zeranol, a radioimmunoassay has been validated for the determination of zeranol residues in the faeces of treated steers. The limit of decision defined as the mean apparent concentration of zeranol in the faeces of untreated cattle + 3 SD was 1 ng/g faeces. In a trial in which 27 steers were implanted with zeranol (36 mg) at the base of the ear and six steers were sham implanted, the mean maximum concentration of zeranol in faeces was 5.8 ng/g on Day 15 following implanting, declining to 1.67 ng/g on Day 34 following implanting. During this period there was a marked variation between animals sampled on the same day following implanting. At no time during the trial did the apparent concentration of zeranol in the faeces of untreated animals rise above 0.91 ng/g, which is below the limit of decision for this assay.

Animals↗
PubMed1986

Radioimmunoassay of the anabolic agent zeranol. IV. The determination of zeranol concentrations in the edible tissues of cattle implanted with zeranol (Ralgro).

Rapid solvent extraction combined with a radioimmunoassay using a monoclonal antibody raised against a derivative of zeranol has been used to measure the residues of the anabolic agent zeranol in the edible tissues (muscle, liver, kidney and fat) of cattle treated with Ralgro. Calibration curves, both with and without, tissue extracts exhibit good parallelism. Regression analysis for the extraction of zeranol from tissues dosed with standard amounts of zeranol have correlation coefficients of 0.979, 0.991, 0.986 and 0.985 for muscle, liver, kidney and fat, respectively. The limits of decision defined as the mean value + 3 SD for the concentrations apparently observed (noise) in tissues from animals not treated with Ralgro were 278, 121, 373 and 110 ng/kg for muscle, fat, liver and kidney, respectively. In the tissues of 4 cows implanted with Ralgro (36 mg), and sampled 70 days after implanting, the highest concentration of zeranol in each tissue was 232 ng/kg (muscle), 391 ng/kg (liver), 287 ng/kg (kidney) and 293 ng/kg (fat), and residues were detected in all samples of fat (4), 3 kidney samples and 1 liver sample.

Adipose Tissue↗
PubMed1986

Radioimmunoassay of the anabolic agent zeranol. V. Residues of zeranol in the edible tissues, urine, faeces and bile of steers treated with Ralgro.

Two trials were conducted on steers implanted with zeranol (Ralgro) to determine the edible tissue residues and the secretion pattern in faeces, urine and bile of zeranol residues throughout and beyond the recommended withdrawal period (70 days) for this drug. In the first trial there was considerable variation in the zeranol residue concentration in all edible tissues, the highest concentrations found in the liver being significantly above the control values (P less than 0.05). In the other tissues, only fat sampled 14 days after implanting was significantly above the control value (P less than 0.05). The zeranol concentration in bile samples obtained at slaughter [70 days (18), 90 days (5) and 120 days (2)] were all higher than the apparent concentration in the bile of untreated steers. The mean concentration of zeranol in the faeces and urine varied from day to day and between animals sampled on the same day following implantation. The highest mean concentrations were observed during the first 40 days following implanting, declining steadily to approach the control values 70 days after implantation. The second trial using steers prepared with bile duct re-entrant cannulae resulted in a similar pattern of zeranol excretion in bile, faeces and urine. The highest concentrations of zeranol were observed in bile and ranged from 24 to 34 micrograms/l; there was considerable variation between animals and within animals sampled on successive days. Although the concentration declined steadily, zeranol was still readily detectable 120 days after implanting.(ABSTRACT TRUNCATED AT 250 WORDS)

Adipose Tissue↗
PubMed1985

An improved radioimmunoassay for the anabolic agent hexoestrol, using a monoclonal antibody.

A monoclonal antibody was raised against hexoestrol coupled to bovine serum albumin. The antibody cross-reacted with the stilbenes, diethylstilboestrol (10%) and dienoestrol (4%), but had no cross-reaction (less than 0.01%) with other anabolic agents. A radioimmunoassay method using the monoclonal antibody has been validated and used to measure residues of hexoestrol in the urine of treated cattle. The limit of detection was 0.6 pg/ml urine at the 95% confidence limit. The results were compared with those obtained using polyclonal antibodies. Although there was a good correlation between the results, the use of monoclonal antibody gave more reliable results than those obtained with available polyclonal antibodies. The monoclonal antibody, because of its quality and theoretically limitless supply, is very suitable for use in large scale screening or monitoring programmes for regulating the use of hexoestrol.

Animals↗
PubMed1984

Preparation and properties of monoclonal antibodies to the anabolic agent zeranol.

Monoclonal antibodies have been produced using two haptens, zeranol-7-hemisuccinate coupled to bovine serum albumin and zeranol-16-carboxypropyl ether coupled to human serum albumin. An assessment of cross-reactivity demonstrated that the monoclonal antibody raised against the 7-hemisuccinate derivative reacted with zeranol (100%), talernol (12%), zearalenone (17%), zearalanone (100%) and alpha- and beta-zearalenol (17% and less than 0.01%, respectively). In contrast the antibodies to the 16-carboxypropyl ether derivative reacted only with zeranol (100%) and also with a alpha-zearalenol (13-16%). All monoclonal antibodies were more specific than the polyclonal antibodies raised to the same haptens by conventional methods using sheep.

Animals↗
PubMed1983

Radioimmunoassay of the anabolic agent zeranol. II. Zeranol concentrations in urine of sheep and cattle implanted with zeranol (Ralgro).

A radioimmunoassay for zeranol has been validated and used to measure the concentration of zeranol in the urine of sheep and cattle treated with zeranol (Ralgro). The assay uses an antibody raised against zeranol-16-carboxy-propyl ether conjugated to human serum albumin. In sheep and cattle urine the limits of detection were approximately 2 ng/ml and 2.5 ng/ml, respectively. In two trials 13 sheep were implanted with 12 mg zeranol at the base of the ear. The mean maximum concentrations of zeranol observed in urine were 45 ng/ml (Trial I) on day 35 and 90 ng/ml (Trial II) on day 56, and had declined to 26 ng/ml 42 days after implantation (Trial I) and 11.7 ng/ml 70 days after implantation (Trial II). In four cattle implanted with 36 mg zeranol the concentrations of zeranol in urine reached a mean maximum concentration of 13.5 ng/ml 22 days after implantation and had declined to 2.9 ng/ml 69 days after implantation.

Animals↗
PubMed1979

Proteins in the uterine secretions of the cow.

Cows of normal reproductive history were treated with progesterone for periods of 2--3 months. The uterine secretions yielded 5 major fractions of macromolecular components. Two of the fractions comprised serum proteins. In the other 3 fractions at least 9 non-serum proteins were observed, 7 in one fraction, but in only small amounts. Of the remaining 2 non-serum proteins one is an acid phosphatase recoverable in small amounts, and the other is lactoferrin and is the major non-serum protein present in the uterine secretions of progesterone-treated cows.

Acid Phosphatase↗
PubMed1976

Manganese metabolism in cows and goats.

When 54MnCl2 was incubated with fresh bovine or caprine serum for 20 h and the serum subjected to electrophoresis at pH 9.5, the 54Mn bound to transferrin and alpha2-macroglobulin in proportions which varied with the temperature of incubation and the temperature of electrophoresis. Between 0 and 37 degrees C, the higher the temperature of incubation the larger the proportion bound to transferrin and the lower the proportion bound to alpha2-macroglobulin. The temperature at which electrophoresis was performed had little effect on the proportion of 54Mn bound to transferrin, but increasing temperature reduced the proportion of 54Mn bound to alpha2-macroglobulin. Mn2+ did not bind to purified transferrin in vitro in the absence of an oxidising agent. In the presence of permanganate, Mn3+ was formed and chelated by transferrin at physiological pH. In fresh serum this oxidation step may be performed by ceruloplasmin or molecular oxygen. Mn2+ was bound reversibly to alpha2-macroglobulin but this protein played no part in the oxidation of divalent manganese and had no effect on the protein binding of trivalent manganese. Manganese in the divalent state, either free as Mn2+ or bound to alpha2-macroglobulin, is removed from blood plasma very efficiently by the liver. However, the manganic-transferrin complex normally found in circulation is not rapidly removed from plasma. The liver can remove large amounts of excess manganous manganese which it presumably excretes; the small essential fraction of the manganese absorbed is oxidised to the trivalent state and bound to transferrin.

Animals↗
PubMed1976

Glycopeptides from bovine liver basement membrane and plasma membrane.

Proteolytic digests of liver plasma-cell membranes from the cow were fractionated to yield two homogeneous glycopeptides and a third preparation about 92% pure. The composition of the two homogeneous glycopeptides made it clear that they were derived from basement membrane material rather than the plasma membrane. Ruminants are unusual in having large amounts of basement membrane in the liver while other animals generally have little or none. Both basement-membrane-derived glycopeptides contained a glucosyl galactosyl disaccharide linked to hydroxylysine, the smaller one contained no other sugar structure but the larger one contained in addition an acidic heterosaccharide, the two chains probably being linked separately to the same molecule. Smith degradation and beta-elimination operations show that this heterosaccharide has an inner structure containing mannose and hexosamine, with the sugars galactose, N-glycollyl-neuraminic acid and fucose situated more peripherally. The amino-acid-heterosaccharide linkage is alkali stable. The third glycopeptide, which may be plasma-membrane-derived, differs from the heterosaccharide described above in that it contains no glucose and contains some O-seryl and O-threonyl amino-acid--sugar linkage. It, too, has a periodate-resistant structure of hexosamine and mannose.

Amino Acids↗
PubMed1976

Iron dynamics in the ruminant.

We have compared the plasma clearance rate of radioactive iron in cows both as ferric chloride and as iron specifically bound to transferrin. We have also repeated the transfusion experiment of Dern et al. (Dern, R.J., Monti A. and Glynn, M.F. (1963) J. Lab. Clin. Med. 61,280-291) using goats. The results show that neither non-specificity bound iron (Bates, F.W. and Schlabach, M.R. (1973) J. Biol. Chem. 248, 3228-3232) nor the iron bound to the two different sites in transferrin (Awai, M., Chipman, B. and Brown, E.B. (1975) J. Lab. Clin. Med. 85,769-784) can be identified as distinguishable iron pools by this technique.

Animals↗
PubMed1973

A new general method for the assessment of the molecular-weight distribution of polydisperse preparations. Its application to an intestinal epithelial glycoprotein and two dextran samples, and comparison with a monodisperse glycoprotein.

A specimen of intestinal glycoprotein isolated from the pig and two samples of dextran, all of which are polydisperse (that is, the preparations may be regarded as consisting of a continuous distribution of molecular weights), have been examined in the ultracentrifuge under meniscus-depletion conditions at equilibrium. They are compared with each other and with a glycoprotein from Cysticercus tenuicollis cyst fluid which is almost monodisperse. The quantity c(-(1/3)) (c=concentration) is plotted against xi (the reduced radius); this plot is linear when the molecular-weight distribution approximates to the ;most probable', i.e. when M(n):M(w):M(z): M((z+1))....... is as 1:2:3:4: etc. The use of this plot, and related procedures, to evaluate qualitatively and semi-quantitatively molecular-weight distribution functions where they can be realistically approximated to Schulz distributions is discussed. The theoretical basis is given in an Appendix.

Animals↗
PubMedDate not supplied

An enzyme immunoassay for the anabolic agent zeranol.

A competitive enzyme immunoassay (EIA) for the detection and quantitation of zeranol has been developed. The assay involves the use of excess second antibody adsorbed onto the walls of a microtitration plate well. Enzyme-labelled zeranol, prepared by the N-succinimidyl ester method, and standard or samples are added to the wells followed by zeranol-specific monoclonal antibody. The working range of the EIA is between 10 and 800 pg/well with a limit of detection of 10 pg/well (CV less than or equal to 10%). Comparison of radioimmunoassay with the EIA gave a correlation coefficient of 0.99. This EIA offers an alternative to the well-documented radioimmunoassay with regard to sensitivity, specificity and precision.

Animals↗