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Biomedical subjects

W Thornburg

Publications and source records attributed to W Thornburg.

At least 19 recordsLinked to original sources
PubMed1987

Effects of enterally fed epidermal growth factor on the small and large intestine of the suckling rat.

Epidermal growth factor (EGF) has been shown to be present in the milk of several species, including the rat, and to have gastrointestinal effects when given parenterally or orally in pharmacologic doses. We investigated the effect of enteral EGF in physiologic doses on the small intestine and colon of suckling rats. Serum thyroxine (T4) levels were also measured. Rats were gavage-fed by hand with an artificial formula with or without added EGF every 3 h from 11 to 14 days of age. Intake was adjusted to deliver 30 kcal/100 g b.wt./day of formula and 16 micrograms/kg/day of EGF approximating the daily caloric intake, and about twice the estimated daily EGF intake for suckling rats. Weight gain did not differ between groups (fed EGF: 3.8 + 0.2 g; not fed EGF: 3.7 + 0.1 g). The protein content of the whole colon of rats fed an EGF-containing formula was significantly lower and the DNA content significantly higher, than in rats fed formula without added EGF. The protein/DNA ratio was therefore markedly higher in the animals fed formula without added EGF; these effects were most evident in the distal colon. In contrast, there was no effect of EGF on small intestinal protein and DNA content; lactase, sucrase, and maltase activities were likewise unaffected, as was serum T4. These data suggest a physiologic role for breast milk EGF in the development of the suckling rat colon.

Animals↗
PubMed1987

Response of activity of jejunal disaccharidases and pancreatic amylase in young and middle-aged rats to a high carbohydrate diet.

Sprague-Dawley rats fed a nonpurified diet from weaning to 3 mo (young) or 12 mo (middle aged) of age were fed a low (5 cal%) starch (LST) purified diet for 2 wk. They were then fed a high (70 cal%) starch (HST) purified diet for up to 4 wk. Body weights of both age groups were greater in rats fed the LST than in those fed nonpurified diet throughout. The young, but not the middle-aged, group continued this gain while consuming HST. The levels of activity of intestinal disaccharidases of upper (proximal one-third) and lower (middle one-third) jejunum, and pancreatic alpha-amylase were lower in rats fed LST diet in both age groups than in rats fed HST. Similar increases of specific (per protein or DNA) activity were observed in both age groups throughout the first three (disaccharidase) to four (pancreatic alpha-amylase) days of feeding HST. Values of specific activity of the middle-aged group returned to initial levels with continued feeding of HST. In contrast, values in the young group tended to plateau (disaccharidases) or continued to increase (alpha-amylase). Differences in adaptability over 1 mo were most dramatic for alpha-amylase and sucrase, but negligible for lactase.

Aging↗
PubMed1987

Effect of maturation on gastrointestinal absorption of epidermal growth factor in rats.

Epidermal growth factor (EGF) was iodinated and administered orally to 13- to 15-day-old suckling rats and 29- to 31-day-old weanling rats. After 30 min, stomach, small intestine, plasma, liver, lung, and skin were removed. The tissues were homogenized and 125I radioactivity was extracted. Compared with suckling rats, the delivery of total radioactivity into peripheral tissues was enhanced in skin of weanling rats and tended to be higher in plasma and liver. In contrast, there was a 3.3-fold reduction in radioactivity remaining in the intestinal wall. Sephadex G-25 chromatography of most samples, especially liver and intestinal wall, revealed a decrease in the proportion of intact 125I-EGF eluting in the void volume. As a result, because the amount of total radioactivity also differed, the overall recovery of radioactivity of void volume 125I-EGF was similar in both age groups except for an increase in skin and a decrease in the intestinal wall of weanling rats. Extracts of all tissues of weanling rats examined contained immunoreactive 125I-EGF. Samples obtained from tissues and content of the gastrointestinal tract of both age groups bound specifically to A431 cell surface receptors. These results thus indicate that EGF is absorbed and delivered to various tissues of weanling rats. Nevertheless, quantitative and qualitative changes in these processes occur during the postnatal period.

Animals↗
PubMed1986

Processing of epidermal growth factor by suckling and adult rat intestinal cells.

Preparations of intestinal villus and crypt cells were isolated from jejunal segments of suckling (14-day-old) and adult (6- to 7-wk-old) rats. These cell preparations were incubated with 125I-labeled epidermal growth factor (EGF) at 37 degrees C to determine the extent of cellular processing of 125I-EGF in vitro. 125I-EGF bound specifically to both crypt and villus cells of suckling rats and was internalized and degraded to similar extents in both cell preparations. Analysis of the 125I radioactivity in the medium and cellular extract by gel filtration on Sephadex G-25 columns demonstrated the presence of [125I]iodotyrosine (24-31%) following 30 min of incubation. This degradation of EGF was accompanied by a loss in the capacity to bind to anti-EGF antibodies (34-52%) and A431 cells (28-48%). Binding, internalization, and processing of 125I-EGF by crypt cell preparations of adult rats was similar to that of suckling rats. In contrast, little degradation of 125I-EGF to iodotyrosine and loss of cell binding capability occurred following incubation with adult villus cells. However, a considerable loss in binding to anti-EGF antibody was detected (48%). The results indicate that isolated intestinal cells are capable of degrading 125I-EGF in vitro in a manner similar to that seen after oral feeding in vivo. They also indicate differences in the processing of 125I-EGF by isolated villus cells of adult compared with suckling rat.

Aging↗
PubMed1986

Isolated pancreatic acini from suckling and weanling rats: changes in amino acid incorporation and carbachol-stimulated amylase secretion with age.

To characterize the changes in pancreatic function during postnatal development, isolated pancreatic acini were prepared from rats aged 8-9, 12-14 and 20 days and from adult rats. Isolated acini maintained a normal microscopic appearance and viability as judged by exclusion of trypan blue and linear incorporation of tritiated leucine into total protein. The rate of incorporation in 8-day-old acini was 20% of that observed in adult rats. Significant dose-dependent increases in amylase release in response to carbachol were observed in all age groups; stimulated amylase secretion was significantly less in the 8- to 9- and 12- to 14-day-old animals than in the 20-day-old and adult rats. These data indicate that viable isolated pancreatic acini can be prepared from suckling rats and that these acini exhibit an altered in vitro responsiveness to carbachol. This preparation should therefore be a useful model for in vitro studies of the development of pancreatic function.

Amino Acids↗
PubMed1986

Processing of hormones and hormone-like substances from milk in the gastrointestinal tract of suckling rats.

Colostrum and milk contain insulin, epidermal growth factor and prostaglandins. Experiments performed in our laboratory have demonstrated that these three substances can be absorbed by the gastrointestinal tract of suckling rats in biologically active form in considerable amounts. Prostaglandins are metabolized by the gastrointestinal tract during postnatal development. There are quantitative and qualitative differences in the metabolism of orally administered prostaglandins between suckling and weanling rats. Nevertheless, a significant amount of intact prostaglandin appears in the liver of suckling rats after oral administration. Gastric administered insulin can result in hypoglycemia. In suckling rats, there is a considerable decrease in blood glucose levels, while no effect is seen in 30-day-old rats. Epidermal growth factor is processed in the gastrointestinal tract as shown by size exclusion and affinity columns and surface receptor binding. Oral administration of epidermal growth factor has several effects on gastrointestinal functions. Analysis of epidermal growth factor processing by the gastrointestinal tract demonstrated postnatal developmental differences (either during normal development, or one accelerated by steroid treatment). These studies show that the gastrointestinal tract can be influenced by orally administered hormones known to be present in milk, and that these substances can be delivered to peripheral organs of suckling animals intact.

Animals↗
PubMed1984

Gastrointestinal absorption of epidermal growth factor in suckling rats.

Epidermal growth factor (EGF) was detected in the milk of adult lactating Sprague-Dawley female rats (38.85 ng/ml) and in the stomach (37.25 ng/g content) and plasma (32.36 ng/ml) of 13-day-old suckling offspring. Sixty-nanogram (0.12 mCi/ml) doses of 125I-EGF were administered orally to sucklings in 200 microliters of buffer for 0, 0.5, 1.0, and 3.0 h. Lung, liver kidney, brain, and blood each contained 1% or less of the administered radioactivity. Stomach wall (8%) and content (63%), intestinal wall (15%) and flushing (38%), and skin (18%) contained larger amounts reaching maxima in these three regions at 0, 0.5, and 3.0 h, respectively. Except for skin, a substantial amount of radioactivity from all tissues represented intact (6-90%) and immunoreactive (3-90%) EGF based on Sephadex G-25 chromatography and anti-EGF antibody binding, respectively. From 30 to 55% of the radioactivity from wall (gastric or small intestinal) or lumina was also capable of binding to A-431 cell surface receptors. Isoelectric points of major species found in stomach (4.2), intestine (4.1), and other tissues differed from that of administered EGF (4.5).

Animals↗
PubMed1982

Precautions in ashing techniques for lead determination in food.

In determining lead in food, the matrix must be destroyed before quantitation by atomic absorption spectrophotometry. Wet or dry ashing techniques are generally used. Dry ashing assisted by ultrapure H2SO4 or K2SO4 has the advantages of safety, low reagent blanks, rapidity, and good recoveries of added lead. These techniques are also less labor-intensive than wet ashing.

Food Analysis↗
PubMed1979

Properties of rat liver nuclear protein kinases.

Two cyclic nucleotide-independent protein kinases (ATP:protein phosphotransferase, EC 2.7.1.37) have been purified to homogeneity from rat liver nuclei. While these enzymes have many similar catalytic properties (preference for acid rather than basic proteins), they differ in molecular weight and subunit composition. Protein kinase NII will utilize ATP and GTP as phosphate donors while protein kinase NI will only effectively use ATP. Both enzymes reveal an unusual activation by Fe2+.

Adenosine Triphosphate↗
PubMed1978

Purification of rat liver nuclear protein kinase NI.

Rat liver nuclear protein kinase NI, which appears in the flowthrough of DEAE-Sephadex columns, has been purified approximately 15,000-fold from soluble nuclear protein with yields of up to 10%. The method of purification involved chromatography of the DEAE-flowthrough protein successively on phosvitin-Sepharose and casein-Sepharose followed by rechromatography on phosvitin-Sepharose. The purified enzyme has an s20,w and molecular weight of 3.7 and 47,000, respectively, as determined by sucrose density gradient centrifugation in 0.4 M NaCl. A similar molecular weight of 42,000 was determined by gel filtration using Sephadex G-100. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the purified enzyme revealed a single polypeptide with a molecular weight of 25,000. Protein kinase NI therefore consists of a dimer of two identical subunits. Protein kinase NI exhibits maximal activity on casein substrate and is not stimulated by 10(-5) to 10(-4) M cAMP or cGMP when either casein or histone H2b is used as a substrate.

Animals↗
PubMed1977

Purification of rat liver nuclear protein kinase NII.

Rat liver nuclear protein kinase activity (NII), which is eluted from DEAE-Sephadex columns, has been purified approximately 1500-fold from solubilized nuclear protein. The method of purification involved chromatography of protein eluted from DEAE-Sephadex successively on phosvitin-Sepharose, mixed histone-Sepharose, and histone H2b-Sepharose followed by gel filtration on Sephadex G-200. Resulting preparations are homogeneous by polyacrylamide gel electrophoresis. The enzyme consists of three polypeptides with molecular weights of 42,000 (alpha), 39,000 (alpha'), and 26,000 (beta) which are present in the ratio 1:1:2 indicating that the enzyme has a minimum tetrameric subunit composition of alphaalpha'beta2. The molecular weight and s20,w of the purified enzyme were 123,000 and 7.0, respectively, as determined by sucrose density gradient centrifugation in 0.4 M NaCl. The enzyme has maximal activity with phosvitin as substrate and is not stimulated by 10(-5) to 10(-4) M cAMP or cGMP using H2b as substrate.

Animals↗