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Biomedical subjects

R A Goodlad

Publications and source records attributed to R A Goodlad.

At least 55 records · Page 3Linked to original sources
PubMed1996

Epidermal growth factor (EGF).

Despite the wealth of information concerning EGF and its related peptides, its precise role in the control of gastrointestinal functions is still not fully resolved. However, there is no doubt that it can have some very potent effects on the gastrointestinal tract. These may be related to the control of growth and development and to the regular control of cell renewal. Nevertheless, in the adult, EGF may only be active in response to luminal damage and repair, and furthermore this may also only occur if the luminal EGF is protected from proteolytic degradation. Notwithstanding this, 'EGF'-like responses may be evoked in the gut by intestinal TGF-alpha. The possible therapeutic use of EGF and members of its family in ulcer therapy will be discussed in later Chapters of this volume, other potential uses are in the control of necrotising enteritis and in the alleviation of the mucositis associated with cancer treatment.

Adult↗
PubMed1996

Comparison of the mitogenic activity of human epidermal growth factor I-53 and epidermal growth factor I-48 in vitro and in vivo.

1. Epidermal growth factor is secreted into the gut lumen as a 53 amino acid peptide in vivo. Several preliminary studies have examined the clinical benefit of recombinant epidermal growth factor in intestinal disease, but there is inconsistency in the form of epidermal growth factor used (some using epidermal growth factor 1-48 and some epidermal growth factor 1-53), making comparisons difficult to evaluate. 2. We therefore examined the relative potency of recombinant epidermal growth factor 1-48 and epidermal growth factor 1-53 in stimulating [3H]thymidine uptake into primary rat hepatocytes at various doses in vitro and on various parameters of proliferation within the gastrointestinal tract when infused intravenously at 50 nmol day-1 kg-1 into rats receiving total parenteral nutrition. 3. Epidermal growth factor 1-53 was about twice as potent as epidermal growth factor 1-48 in its ability to stimulate [3H]thymidine incorporation into rat hepatocytes in vitro. In vivo studies supported this finding as, in both the small and large intestine, epidermal growth factor 1-53 caused about a 30% greater stimulation of intestinal growth than epidermal growth factor 1-48 (P < 0.001). 4. The 1-48 truncated form of epidermal growth factor is less active than the full-length molecule in vitro and in vivo. This must be borne in mind when comparing clinical trials that use different forms of recombinant epidermal growth factor.

Animals↗
PubMed1996

Comparison of the effects of transforming growth factor alpha and epidermal growth factor on gastrointestinal proliferation and hormone release.

Epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) bind to a common receptor and are both present in the normal gastrointestinal tract. Although many studies have examined their function in isolation, there is little information directly comparing their actions. We examined the relative potency of TGF alpha and EGF in stimulating 3H-thymidine uptake into primary rat hepatocytes at various doses in vitro and on the crypt cell production rate (CCPR) within the gastrointestinal tract when infused intravenously at 49 nmol/kg/day into rats receiving total parenteral nutrition. In vitro, maximal stimulatory activity was similar in EGF- and TGF alpha-treated cells, however, the dose of EGF required to stimulate 3H-thymidine uptake to 50% of maximal levels was only one third of that required using TGF alpha. In vivo, EGF and TGF alpha significantly increased the weight and proliferative indices throughout the gastrointestinal tract. The response (as determined by CCPR) was about 80% higher in animals which had received EGF when compared to animals receiving TGF alpha. Treatment with EGF also caused significant rises in plasma PYY, enteroglucagon and gastrin levels, whereas the equivalent dose of TGF alpha only caused a significant rise in plasma gastrin levels. We conclude that TGF-alpha, like EGF, is trophic to the entire gastrointestinal tract of the rat, however, it is a less effective mitogen, and has differential hormonal effects.

Animals↗
PubMed1995

The effects of and interactions between fermentable dietary fiber and lipid in germfree and conventional mice.

BACKGROUND/AIMS: Dietary fiber can stimulate intestinal epithelial cell proliferation. The aim of this study was to resolve the different roles of fermentation and intraluminal viscosity on this trophic action and to investigate reported interactions between fiber and dietary fat. METHODS: Conventional and germfree mice were fed guar gum in combination with low- or high-lipid diets for 2 weeks, and crypt cell production rates were determined. RESULTS: Guar gum significantly stimulated proliferation in the small intestine, especially when combined with fat. Lipid itself also stimulated proliferation in the small intestine and had a direct trophic effect in the cecum and colon of the germfree mice. Fiber markedly stimulated proliferation in the cecum and colon but only in the conventional group. Interactions between lipid and bacteria and between guar gum and bacteria were also observed in the small intestine. CONCLUSIONS: Guar gum has a trophic effect in the small bowel, probably related to viscosity, in addition to its fermentation-related actions in the colon. Positive interaction with lipid may be associated with delayed absorption. Lipid also has its own direct actions on small bowel mucosal proliferation, which are attenuated by the presence of bacteria.

Animals↗
PubMed1995

Luminal epidermal growth factor is trophic to the small intestine of parenterally fed rats.

1. Intestinal atrophy contributes to the clinical difficulties of patients on parenteral nutrition. Systemic administration of epidermal growth factor reverses this effect, but there is concern over the clinical safety of intravenous administration of growth factors. We therefore investigated whether administration of luminal epidermal growth factor could reverse the atrophy induced in a rat model of parenteral nutrition when epidermal growth factor was given alone or in combination with soya bean trypsin inhibitor to reduce proteolytic digestion of the epidermal growth factor. 2. Infusion of soya bean trypsin inhibitor alone decreased intraluminal tryptic activity by about 90% but did not result in increased proliferation. Intragastric infusion of epidermal growth factor (72 micrograms/day per rat) caused a 26% increase in proliferation (determined by 2-h metaphase arrest) in the duodenum (P < 0.01) when compared with animals receiving 'control' intragastric infusion. However, intragastric epidermal growth factor had no effect on more distal regions of the bowel, probably reflecting rapid proteolysis of the epidermal growth factor by luminal proteases. In contrast, a trophic effect of luminal epidermal growth factor was seen in the duodenum (28% increase, P < 0.01) and jejunum (24% increase, P < 0.05) of animals which had received epidermal growth factor with soya bean trypsin inhibitor. This was probably due to the soya bean trypsin inhibitor decreasing the rate of degradation of epidermal growth factor by intestinal proteases, allowing biologically active epidermal growth factor to reach more distal portions of the bowel.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Epidermal growth factor and transforming growth factor-alpha actions on the gut.

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) are part of a large family of ligands that bind to the epidermal growth factor receptor. While the precise role of these ligands is still unclear, there is little doubt that they play an important role in the development and maintenance of gastrointestinal epithelial continuity. The main ligand for the intestinal EGF receptor (EGFR) may in fact be TGF-alpha, and there is evidence that EGF itself may act as a surveillance factor in adults, only having an effect if the mucosa is damaged.

Adult↗
PubMed1995

Gastrin and the growth of the gastrointestinal tract.

While the proliferative effects of gastrin in the gastric fundus are well established, there is a considerable degree of confusion regarding the role of gastrin on the growth of the small intestine and colon. The hypothesis that gastrin is trophic throughout the gut was tested by giving three doses of pentagastrin and one of gastrin 17 to rats maintained by total parenteral nutrition (TPN). The rats were fed intravenously for one week, with the various peptides added to the TPN diet. The number of vincristine arrested metaphases per gland or crypt was then scored to determine the proliferative state. Both gastrin 17 and pentagastrin were found to be trophic in the gastric fundus, but not to the gastric antrum. A proliferative response was also seen in the duodenum, but with little evidence of a dose response element. No effect on small bowel weight was seen, and no proliferative effect was noted in the mid small bowel, thus the duodenal effect could be attributed to a local action of increased acid output on the duodenum, not a general role throughout the small intestine. No proliferative effects of pentagastrin or gastrin were seen in the colon. It is therefore concluded that the trophic role of gastrin is restricted to the gastric fundus and the proximal duodenum.

Animals↗
PubMed1995

Crypt fission in the small intestine and colon. A mechanism for the emergence of G6PD locus-mutated crypts after treatment with mutagens.

In the small intestine and colon, administration of mutagens leads to the emergence of crypts populated by cells with a different, mutated phenotype. This is preceded by a transient rise in the frequency of crypts with a partially mutated phenotype, and the disappearance of these partially mutated crypts occurs contemporaneously with the attainment of a plateau value of the wholly mutated crypts. Here, using the mutagen ethyl nitrosourea and loss of glucose-6-phosphate dehydrogenase staining as a marker, we show that the plateau is reached at between 4.6 and 7 weeks in the colon and at 12 weeks in the small intestine of the same mice. Explanations for this difference have included differences in the stem cell cycle time of a single "master" stem cell or multiple stem cells occupying a stem cell "niche" with random loss after stem cell division. However, we demonstrate that the crypt fission index, or the incidence of crypts in fission, is some four times higher in the colon than in the small intestine at the time of ethyl nitrosourea injection, and propose an alternative hypothesis based on crypt fission as the mechanism for the more rapid evolution of wholly mutated crypts in the colon. The hypothesis should enable us to predict the results of future experiments, namely that the emergence of wholly mutated crypts is proportional to the crypt fission index.

Animals↗
PubMed1994

Proliferating cell nuclear antigen expression in non-cycling cells may be induced by growth factors in vivo.

The proliferating cell nuclear antigen (PCNA) is required for DNA replication and DNA nucleotide excision repair. Considerable evidence points to PCNA expression being a marker of proliferation in many situations. However, while levels of PCNA are normally very low in non-cycling tissues, high levels of the protein have been observed in the normal tissues surrounding human breast and pancreatic tumours. Using two model systems we have shown that PCNA is induced in non-cycling cells by adjacent transplanted tumour cells and that this phenomenon may be mimicked by the in vivo administration of growth factors (transforming growth factor alpha and epidermal growth factor). These data suggest that tumours may elaborate factors that induce PCNA expression in nearby normal cells. PCNA induction the normal cells surrounding tumours is a direct example of the effect of tumour cells on normal surrounding tissues. This effect may prove to be a useful parameter in the analysis of tumour-host interactions.

Animals↗
PubMed1994

Maintenance of normal intestinal mucosa: function, structure, and adaptation.

Diet is of fundamental importance in the healthy functioning of alimentary epithelium, or during the disease process. Specifically, the incidence of 'non-hereditary' gastrointestinal disease varies widely throughout the world, partly because of different cultural and dietary habits. The aim of this review is to outline the mechanisms that modulate normal mucosal development and growth in the small and large intestine. In addition a brief mention will be made of morphological changes in certain pathological conditions.

Gastrointestinal Diseases↗