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D R Appleton

Publications and source records attributed to D R Appleton.

At least 19 recordsLinked to original sources
PubMed1996

An organ-culture method for human colorectal mucosa using serum-free medium.

This study describes an explant organ-culture system in which human colonic mucosa can be maintained for prolonged periods in serum-free medium. Following an initial phase of epithelial cell loss, there was intense regenerative activity, with the reformation of tubular crypts. Estimation of crypt lengths revealed a marked reduction after 5 and 9 days in culture with corresponding increases in labelling indices for the whole crypt. The shapes of bromodeoxyuridine (BrdU)-flash-labelling distribution curves were consistent with a proliferative compartment situated within the lower two-thirds of the crypt. We conclude that this is a useful in vitro model for the study of the effects of growth factors and growth-inhibitory agents in respect of cell proliferation in human colonic mucosa.

Bromodeoxyuridine↗
PubMed1995

What do we mean by a statistical model?

Statisticians are too often satisfied by fitting data rather than investigating the process out of which the data arose. The assumptions on which they base their models may be quite unrealistic, and while it is true that a model should not be more complicated than necessary, neither should it be too simple. Ways of approaching several sets of data from different areas of clinical medicine are considered, and different attitudes to the purpose of modelling highlighted. The transition from smoothing data, through fitting curves, to modelling underlying processes is discussed.

Analysis of Variance↗
PubMed1993

An application of the truncated Poisson distribution to immunogold assay.

An example of the use of the truncated Poisson distribution in an immunogold assay of dystrophin, a gene product of importance in the study of muscular dystrophies, is presented. The practical benefit of using minimum variance unbiased estimators of relevant functions of the parameter of the distribution is considered.

Analysis of Variance↗
PubMed1993

Anti-glomerular basement membrane glomerulonephritis (anti-GBM GN) in the mouse: BrdU-labelling indices and histological damage.

In-vivo BrdU incorporation and visualization by immunohistochemistry, previously reported in normal mouse kidney, were applied to a mouse model of anti-GBM GN, induced by immunization with rabbit anti-mouse GBM antiserum, to assess the contribution of capsular cell proliferation in the development of crescents. A significant increase (P = 0.003) in the BrdU-labelling index (LI) for capsular cells was observed, as compared to normal mice (5.76 +/- 1.1 vs 0.70% +/- 0.12%). Elevated LI were also observed for tuft and tubular cells but these increases were not statistically significant. It was concluded that, in this model, capsular cell proliferation is a major contributory factor to the formation of cellular crescents. In addition, other pathological features, indicative of glomerular damage, were assessed semi-quantitatively alongside numbers of labelled capsular cells per glomerulus. It was found that podocyte vacuolation is strongly associated with, and may precede, proliferation, suggesting some common causative factor. Fibrin, when present, was confined within the tuft capillary loops and was only weakly associated with either podocyte vacuolation or capsular cell proliferation. It was concluded that this protein does not play a major role in the initiation of pathological damage. Finally, glomerular lesions were found to be randomly distributed. Thus, the idea of intraglomerular signalling, resulting in 'clustering' of damaged glomeruli, is not supported.

Animals↗
PubMed1991

Modulation by verapamil of vincristine pharmacokinetics and sensitivity to metaphase arrest of the normal rat colon in organ culture.

The in-vitro pharmacokinetics of vincristine (VCR) in normal rat colonic mucosa were studied. Two complementary approaches were adopted using an explant organ-culture system. Firstly [G-3H]vincristine (3HVCR) accumulation, retention and efflux were characterized under basal conditions and compared with measurements made either under energy-depleted conditions, or in the presence of VRP. Secondly, a histological method--the postmetaphase index (PMI)--was used to compare the sensitivity of explants to VCR in the presence or absence of verapamil (VRP). This latter technique involves the measurement, by counting, of the proportion of mitotic figures escaping from metaphase arrest. The studies yielded the following results: 3HVCR accumulation in colonic mucosa showed no evidence of saturability up to the maximum dose studied (130 nM), at a dose of 52 nM accumulation was enhanced in energy-depleted conditions by a factor of 1.8, and in the presence of VRP (6.6 microM) by a factor of 1.4. In the presence of VRP (6.6 microM) retention of 3HVCR was increased by a factor of 1.3 and efflux was reduced by a factor of 0.8 after 2 hr. VRP (6.6 microM) reduced the PMI of colonic mucosal epithelial cells exposed to 11 nM VCR from 18.8% to 11.4% (i.e. 40% reduction) indicating sensitization of the cells to this property of VCR. These results provide evidence that the sensitivity of normal colonic mucosa to vincristine is, at least in part, regulated by drug transport. Qualitatively our observations resemble those described in multidrug resistance. Given that P-glycoprotein has been demonstrated by several groups in colonic mucosal cells, the results support a normal role for this membrane transport molecule in the protection of intestinal cells from plant alkaloids and other xenobiotic agents ingested in the diet.

Animals↗
PubMed1991

Effects of gastrointestinal peptides on azoxymethane-treated colonic mucosa in vitro.

An organ-culture system has been used to investigate the effect of certain gastrointestinal peptides on the morphology and cell proliferation of explants of azoxymethane (AOM)-treated colonic mucosa. Our aim was to ascertain whether such factors play a direct part in the maintenance of hyperplastic changes in the large intestine. Explants of AOM-treated colonic mucosa from 15 animals were maintained in a serum-free medium in the presence of either gastrin-17 (250 pg/ml and 250 ng/ml), peptide YY (80 pmol/l and 160 pmol/l) epidermal growth factor (EGF) (10 ng/ml and 100 ng/ml) or the C-terminal fragment of glucagon-37 (30 pmol/l) for a period of up to 7 days. Other explants (controls) received fresh medium only each day. After 1, 2, 3, 5 and 7 days of culture both experimental and control explants received vincristine (4 micrograms/ml) for 3 h prior to fixation. The proportion of vincristine-arrested metaphases within the explants was determined together with crypt length. Neither gastrin nor peptide YY was found to influence cell division at either concentration. Despite an initial inhibitory effect, both concentrations of EGF exerted a trophic effect which increased with time. The glucagon-37 fragment caused an immediate increase in proliferation which then declined as time progressed. None of these factors, however, were able to maintain the hyperplastic changes seen in the pre-culture samples of AOM-treated mucosae.

Animals↗
PubMed1990

What statistics should we teach medical undergraduates and graduates?

It is suggested that the emphasis on teaching statistics to medical undergraduates has usually been quite wrong: that the courses have become much too long, too detailed, and irrelevant to the needs of the majority. Examples are given which may help to introduce the basic concepts which all medical (and dental) undergraduates require, and which form a basis for the more traditional teaching of analytical methods to the appropriate subset who proceed to undertake medical research.

Curriculum↗
PubMed1990

The use of computer simulation in the design and analysis of cell proliferation experiments.

The simulation language CELLSIM is used to model a population of cells undergoing proliferation, death and migration. It is shown that standard analytical methods can successfully describe the system in its unperturbed state, but may be considerably in error if the system has recently been subjected to cytotoxic insult. It is suggested that laboratory experiments should be performed on perturbed systems only if simulations have shown that the methods of data analysis will be satisfactorily powerful and accurate.

Animals↗
PubMed1990

The effect of sulindac on colonic tumour formation in dimethylhydrazine-treated mice.

Dimethylhydrazine has been used to produce colonic tumours in mice. If sulindac, a non-steroidal anti-inflammatory drug, is administered simultaneously fewer microadenomata and fewer macroscopic tumours are produced. Those which do appear are comparable in size to the ones in the mice which do not receive sulindac. Sulindac therefore appears to exert an anti-tumour influence at the stage between dysplasia and the formation of microadenomata.

Adenoma↗
PubMed1990

Particle release from haemodialysers.

Release of particles from eight makes of hollow-fibre and one make of flatplate dialyser have been studied, and the relationship between rinsing volume and particles recovered established. In a supplementary study the effect on the number of particles released was assessed when striking the dialyser header during priming. Particle size distribution indicated that the majority of the particles recovered were less than 5 microns in diameter. A separate analysis of the particles in the 5-30 micron size range showed two different patterns of particle release. In the dialysers containing ethylene vinyl acetate (EVAL) or Cellulate the number of particles recovered were within the 95% range of the particles in the rinsing fluid and did not alter with increasing rinsing volume. In the dialysers containing Cuprophan and Hemophan the initial particle numbers were higher but fell rapidly up to a 450 ml rinse volume; increasing the rinse volume to 1050 ml did not alter particle recovery. Analysis of variance failed to differentiate between individual dialysers. Striking the header during priming resulted in a transient statistically nonsignificant increase in the number of particles recovered.

Biocompatible Materials↗
PubMed1990

Anti-glomerular basement membrane (GBM) glomerulonephritis in the mouse: development of disease and cell proliferation.

In a mouse model of anti-glomerular basement membrane (GBM) glomerulonephritis, associated with the nephrotic syndrome, a wide range of morphological and proliferative responses was seen in the renal corpuscle, at 6 days. The severity of the damage could be assessed by measuring the average daily weight gain between days 0 and 3 (DWG) of the animal. Those animals with a high DWG showed capsular proliferation, whereas animals with a low DWG showed predominantly tuft cell proliferation. Capsular cell birth rate increased with DWG whilst tuft cell birth rate was negatively related. A computer simulation suggests that the results are compatible with the induction of successive but overlapping waves of tuft and capsular cell proliferation.

Animals↗
PubMed1989

Proliferative status of colonic mucosa in organ culture: 3H-thymidine-labelling studies and computer modelling.

3H-thymidine labelling studies and a computer simulation have been employed to assess proliferative status and cellular organisation in colonic explants maintained in culture for 5 to 7 days. The one-hour flash labelling index (Is) for crypts within the middle region of explants (5.2%) was considerably lower than that observed in vivo (8.8%). Crypt length and the distribution of labelled cells appeared similar for both situations. A computer simulation program for crypt-cell proliferation was devised, facilitating the modulation of a number of parameters including the cell-cycle time (Tc) and its component phases, the cut-off position, and cell loss at mitosis. This simulation was employed to model continuous labelling (72 h) data obtained in vitro and provided an estimate of various kinetic parameters. Data for the middle region of explants was fitted with a Tc of 62 h, an S phase of 8 h and a cell loss factor (20%) which was consistent with histological findings. A fit to the experimental data obtained in vitro could be achieved by a model based upon a mode of cellular organisation known to occur within crypts in vivo. Therefore in vitro, the dynamic processes of crypt-cell proliferation and migration appear to be organised in the same manner as seen in vivo.

Animals↗
PubMed1989

A protocol for the routine measurement of lactate and pyruvate in cord blood.

The influence of the site of sampling and the delay in sample collection on cord blood concentrations of lactate and pyruvate were investigated. A delay in sample collection of greater than 1 min after cord clamping could invalidate the results obtained. Samples from umbilical artery had higher lactate values (mean 3.13 mmol/l) than paired vein samples (mean 2.32 mmol/l) but there were no significant differences in lactate values between different sites sampled within the umbilical vein. A calculation was devised to circumvent the need to take cord blood samples immediately after delivery.

Blood Specimen Collection↗
PubMed1988

A protective effect of sulindac against chemically-induced primary colonic tumours in mice.

Sulindac, a non-steroidal anti-inflammatory drug, has been reported to lead to tumour regression in cases of human polyposis coli. We have investigated the effects of this drug on the growth of 1,2-dimethylhydrazine (DMH)-induced mouse colonic tumours. In one experiment, DMH and oral sulindac were administered concurrently to a group of mice for a period of up to 24 weeks, while a control group of animals received DMH only for the same period. Sulindac caused a significant reduction in both the number of mice with colonic tumours and the number of tumours per mouse. In a second experiment, two groups of mice which had already been treated with DMH for 17 weeks received either sulindac or not for 78 days. In this experiment sulindac had no effect. These results demonstrate that sulindac has a protective effect against the chemical induction of colonic tumours in mice, but does not cause the regression of established tumours.

1,2-Dimethylhydrazine↗