Search PubMed⌕ Search

Biomedical subjects

G M Levine

Publications and source records attributed to G M Levine.

At least 37 records · Page 2Linked to original sources
PubMed1987

Quantitative immunocytochemistry by digital image analysis: application to toxicologic pathology.

Recent advances in immunocytochemical techniques allow the localization of specific antigens in tissue sections. The work reported here attempts to evaluate the application of antibody-labeled, disease-related protein, followed by microscopy and computerized image analysis. Using an experimental anti-tumor, polyclonal antibody (anti-oncomodulin) as a model, various tissues were prepared for light microscope immunocytochemistry. Sections were incubated with primary antibody, then biotinylated secondary antibody. This was followed by incubation with avidin-biotin-peroxidase (ABC method). Marker was visualized by the presence of precipitated diaminobenzidine. Samples were evaluated using a Zeiss/Kontron IBAS I & II semi-automatic digital image analysis system. Statistical analyses were performed on output data. Results demonstrated the localization and determined optical density of immunolabel. Statistical comparisons showed significant differences between control and experimental sections. The practical application of these combined techniques provides the toxicologic pathologist with a powerful tool for accurate and objective determination of the location and relative amount of selected proteins in normal and abnormal tissues.

Calcium-Binding Proteins↗
PubMed1986

Nonspecific adaptation of jejunal amino acid uptake in the rat.

Luminal nutrients are a major effector of intestinal adaptation. Amino acids are trophic to the intestine, but their role in regulating amino acid transport is not well documented. The presence of several distinct amino acid transport systems raises the question of whether adaptation is class-specific. Studies were carried out in parenterally nourished rats receiving a 7-day jejunal infusion of a 3% solution of either aminoisobutyric acid, aspartic acid, glutamine, histidine, lysine, or valine. While all amino acids were trophic to the intestine, their effects on the in vitro uptake of 0.1, 1.0 and 10.0 mM aspartic acid, lysine, and valine (representative acid, basic, and neutral amino acids) were variable and nonspecific. Compared to controls receiving either total parenteral nutrition alone or total parenteral nutrition plus luminal saline, prior lysine and aspartic acid infusion significantly increased in vitro uptake of all three amino acids tested, whereas valine had little effect on transport. No effect on transport was seen with glutamine (actively metabolized by the intestine as is aspartic acid), aminoisobutyric acid (a nonmetabolizable amino acid congener), or histidine (the most trophic amino acid). In conclusion, while individual amino acids cause an adaptation of amino acid uptake, the effects are nonspecific and independent of their metabolic or trophic potential.

Amino Acids↗
PubMed1985

Intestinal triglycerides are derived from both endogenous and exogenous sources.

Although studies have indicated that the small intestine is capable of utilizing endogenous substrates for triglyceride synthesis in the absence of dietary lipid, the importance of the endogenous contribution to total intestinal triglyceride production during absorption has not yet been defined. In this study we have examined the quantitative contribution of endogenous triglyceride production during different luminal lipid loads. By use of a mesenteric lymph fistula rat model with total parenteral nutritional support, mesenteric lymphatic triglyceride transport was investigated. Our results indicate that, during absorption, a substantial fraction (greater than 50%) of total triglyceride is derived from endogenous sources. Increased luminal fatty acid loads lead to an increase in both endogenous and exogenous triglyceride production. Incorporation of luminally infused oleic acid into triglyceride carried by chylomicrons is dependent on the luminal fatty acid load, while incorporation of oleic acid into very low-density lipoprotein (VLDL) triglyceride is saturable. We conclude that both chylomicron and VLDL are involved in transporting triglyceride derived from both endogenous and exogenous sources. The different patterns in the partition of endogenous and exogenous triglyceride into chylomicrons and VLDL suggest that these two lipid-carrying lipoproteins are probably packaged differently in the small intestine.

Animals↗
PubMed1984

Assessment of resolution by half distance values for tritium and radioiodine in electron microscopic radioautographs using Ilford L4 emulsion developed by "solution physical" or D-19b methods.

Half distance values for electron microscopic (EM) radioautographs with the isotopes 3H and 125I were determined using Ilford L4 emulsion processed with either fine grain, solution physical development, or filamentous grain, chemical development with D-19b. 3H- and 125I-line sources, obtained by cutting perpendicular sections from sections of 3H-labeled methacrylate or 125I-labeled thyroid glands, were processed for EM radioautography. The distribution of silver grains around a line source was determined by measuring their distance from the source in photographs of EM radioautographs. The number of silver grains per unit distance from the line source was plotted on graphs and half distance values were calculated. With solution physical development, the half distance value was 74 nm for 3H and 80 nm for 125I; whereas with D-19 b development it was 187 nm for 3H and 157 nm for 125I. Since solution physical development produced a reduction of about 50% in the half distance values for both isotopes, it is concluded that the production of fine grain by this method provides better resolution for EM radioautography than filamentous grain development with D-19b.

Autoradiography↗
PubMed1983

A model for the reaction pathways of the K+-dependent phosphatase activity of the (Na+ + K+)-dependent ATPase.

(Na+ + K+)-dependent ATPase preparations from rat brain, dog kidney, and human red blood cells also catalyze a K+ -dependent phosphatase reaction. K+ activation and Na+ inhibition of this reaction are described quantitatively by a model featuring isomerization between E1 and E2 enzyme conformations with activity proportional to E2K concentration: (formula; see text) Differences between the three preparations in K0.5 for K+ activation can then be accounted for by differences in equilibria between E1K and E2K with dissociation constants identical. Similarly, reductions in K0.5 produced by dimethyl sulfoxide are attributable to shifts in equilibria toward E2 conformations. Na+ stimulation of K+ -dependent phosphatase activity of brain and red blood cell preparations, demonstrable with KCl under 1 mM, can be accounted for by including a supplementary pathway proportional to E1Na but dependent also on K+ activation through high-affinity sites. With inside-out red blood cell vesicles, K+ activation in the absence of Na+ is mediated through sites oriented toward the cytoplasm, while in the presence of Na+ high-affinity K+ -sites are oriented extracellularly, as are those of the (Na+ + K+)-dependent ATPase reaction. Dimethyl sulfoxide accentuated Na+ -stimulated K+ -dependent phosphatase activity in all three preparations, attributable to shifts from the E1P to E2P conformation, with the latter bearing the high-affinity, extracellularly oriented K+ -sites of the Na+ -stimulated pathway.

Animals↗
PubMed1983

Effects of cholecystokinin and secretin on intestinal structure and function.

Cholecystokinin and secretin are believed to be trophic gastrointestinal hormones. Studies were designed to determine whether these hormones exert their effect through stimulation of endogenous secretion. First, four groups of parenterally nourished rats underwent bypass of the proximal two-thirds of the intestine. One group received secretin, another cholecystokinin octapeptide (CCK-OP), another CCK-OP plus secretin, while the fourth group served as control. After 1 wk, animals were killed; pancreas and segments of intestine were removed. First, mucosal weight, protein content, and fatty acid esterification activity were affected only in intestine in continuity with endogenous secretions after hormone administration. Second, the effects of these hormones were tested in chow-fed rats. The hormone-treated group, despite pancreatic hyperplasia, had similar indexes of intestinal mass compared with pair-fed controls. We conclude that CCK-OP and secretin mediate their trophic effects on the small intestine indirectly, probably through stimulation of pancreatic secretion. In addition, the effects of luminal nutrients have complex interactions with these hormones.

Animals↗
PubMed1983

Effects of luminal glucose versus nonnutritive infusates on jejunal mass and absorption in the rat.

These studies were designed to better understand the effects of luminal nutrition on intestinal mass and function. Parenterally nourished rats received a midjejunal infusion of either 0.9% saline, 10% glucose, 10% 3-O-methyl glucose, or 30% glucose. A fifth group underwent sham operation. After 7 days, intestinal mass and in vitro glucose and leucine uptake were measured in the intestine just distal to the infusion site. Luminal infusion led to greater intestinal mass in all groups compared to controls, but only the 10% and 30% glucose groups had significantly greater overall glucose uptake. Kinetic analysis revealed a greater apparent maximal transport rate in both glucose groups. The 30% glucose group had a greater apparent maximal transport rate for leucine and permeability for glucose and leucine. These data confirmed that "work load," in addition to luminal nutrition, maintains intestinal mass. However, adaptation of intestinal transport is more specific and appears to be regulated both by substrate metabolism and caloric density.

Animals↗
PubMed1982

Characteristics of intestinal glucose secretion in normal and diabetic rats.

A method was developed to characterize and quantitate the transfer of glucose from the plasma to the intestinal lumen. In normal rats, there was a linear correlation between the blood glucose concentration and the rate of appearance of plasma glucose into the intestinal lumen perfused with Krebs-Ringer buffer (r = 0.88, P less than 0.01). Intestinal perfusion with buffers containing either mannitol, glucose, or phlorizin significantly increased the recovery of secreted glucose compared with plain buffer. Rats perfused with buffer containing mannitol or those undergoing plasma volume expansion with dextran demonstrated a change in water movement from net absorption to secretion coupled with a significant increase in glucose secretion. During luminal perfusion with a buffer containing 21 mM glucose, glucose secretion represented 14% of the net glucose absorption rate. Intestinal perfusion with phlorizin gave the highest measured recovery of glucose, probably by blocking active reabsorption of secreted glucose. A series of simultaneous perfusions performed in the jejunum and ileum revealed similar rates of glucose transfer in both segments of intestine. Measurement of glucose secretion in rats with streptozotocin diabetes gave the highest values for the plasma-to-lumen movement of glucose. Treatment with insulin reduced the blood sugar and glucose transfer rate. These data demonstrate that glucose moves bidirectionally across the rat intestine, and its secretion is a passive process.

Animals↗
PubMed1981

Nutritional support in gastrointestinal disease.

Nutritional support is capable of spontaneously healing many gastrointestinal fistulas, particularly if the fistula arises from bowel that is not involved with inflammatory bowel disease or a malignant growth. The choice of either enteral or parenteral nutrition can be used in the treatment of any fistula, the use of enteral nutrition should be more selective. It is recommended that enteral therapy for an upper gastrointestinal fistula be carried out by distal infusion of the diet by either tube or operative jejunostomy. Infusion of the diet distal to the site of the fistula should not increase drainage of the fistula. If drainage does increase in response to enteral feeding, then enteral therapy should be discontinued, and parenteral therapy should be started. Similarly, a fistula of the ileum or colon may also be treated with enteral therapy into the proximal bowel as long as sufficient length of normal bowel exists to absorb the diet proximal to the fistula.

Colitis, Ulcerative↗
PubMed1981

Intestinal fatty acid esterification activity in jejunoileal bypass patients.

In four patients undergoing reversal of jejunoileal bypass we compared functional (in continuity) with bypassed intestine in order to determined the effects of luminal contents. Total mucosal thickness, villus height, and crypt depth, as well as in vitro fatty acid esterification activity were determined. Morphological studies in segments exposed to luminal contents revealed that the ileum had a greater mucosal thickness than the jejunum (p less than 0.001) and that the difference was reflected in both villus height and crypt depth (p less than 0.001). The functioning segments of both jejunum and ileum had a greater mucosal thickness than corresponding bypassed segments consequent to a difference in villus height (p less than 0.001) but not crypt depth. Despite similar exposure to luminal contents, total fatty acid esterification was significantly higher (p less than 0.001) in the functioning jejunum than in the ileum. Jejunum incontinuity possessed higher esterification activity than bypassed jejunum. These results indicate that 1) luminal contents are the most important modulator of intestinal fatty acid esterification activity and the absence of luminal contents in bypassed intestine leads to a significant reduction in esterification activity, 2) the jejunum and ileum possess intrinsic differences in esterification activity even when both are exposed to an identical luminal environment.

Adult↗
PubMed1981

Effects of luminal nutrition and metabolic status on in vivo glucose absorption.

Luminal nutrients, but not metabolic status, maintain active glucose transport by the rat intestine in vitro. The present study was designed to examine the effects of these factors on the in vivo absorption of glucose and 3-O-methylglucose. Rats were fed either intraluminally or by total parenteral nutrition (TPN) for 7 days or fasted for 72 h. Sugar absorption was measured under pentobarbital sodium (Nembutal) anesthesia at concentrations from 7 to 28 mM. Luminally fed rats had a significantly greater mucosal mass and absorption rates per centimeter of both sugars than either TPN or fasted animals. However, TPN rats had significantly greater absorption per milligram protein (i.e., specific activity) for both glucose and 3-O-methylglucose than luminally fed rats. In addition, TPN rats absorbed significantly more glucose per milligram protein, but not 3-O-methylglucose, than fasted animals. These data indicate: 1) luminal nutrients maintain glucose absorption by their trophic effects on mucosal mass; 2) the increase in specific activity for sugar absorption after TPN is unrelated to caloric balance; and 3) intestinal glucose metabolism affects its rate of absorption of glucose, but not 3-O-methylglucose.

Animals↗
PubMed1980

Effect of toal parenteral nutrition on gastric acid secretion.

While total parenteral nutrition is widely used, its effects on gastrointestinal function are not well understood. We measured acid secretion in 11 patients during total parenteral nutrition. Five of these patients were retested at least one month after resuming oral intake. Total parenteral nutrition significantly stimulated acid secretion compared to saline infusion (5.5 +/- 2.0 vs 1.8 +/- 0.6 mEq H+/hr, P less than 0.001) (mean +/- SEM), especially in those patients who are hypersecretors. There was no difference in pentagastrin-stimulated maximal acid output during TPN or saline infusion. Basal and pentagastrin-stimulated acid secretion were similar during and after a course of total parenteral nutrition, suggesting that gastric atrophy did not occur during total parenteral nutrition therapy.

Blood Glucose↗
PubMed1980

Effect of pentagastrin on rabbit stomach and small intestinal protein synthesis.

In an vitro organ culture system, we studied the effects of pentagastrin on rabbit fundic mucosa and small intestinal protein synthesis. The incorporation of [14C]leucine into protein was measured after 24 hr of incubation at 37 degrees C in a 95% oxygen-5% CO2 atmosphere. Biopsies were taken from the stomach, duodenum, jejunum, and ileum of rabbits fasted for 64 hr. Pentagastrin (0.5 microgram/ml) significantly increased protein synthesis in stomach explants at the 24-hr period but did not significantly increase protein synthesis in the duodenum, jejunum, or ileum explants. The results of these in vitro experiments may indicate that pentagastrin is not trophic for rabbit small intestine or, in contrast to its direct effect on the fundic mucosa, pentagastrin acts indirectly in the previously noted in vivo stimulation of intestinal protein synthesis.

Animals↗
PubMed1980

Effects of nutrients, endogenous secretions, and fasting on in vitro glucose uptake.

The effect of luminal nutrients, endogenous secretions, and metabolic balance on the initial velocity of glucose uptake was measured in everted rings of rat intestine. Animals were fed either by total parenteral nutrition (TPN), or into the midjejunum for 7 days, or fasted for 72 h. Luminal feeding resulted in higher midjejunal glucose uptake per milligram of protein, DNA, and centimeter gut length, when compared to fasting or TPN. Kinetic analysis revealed a higher "apparent" Vmax in the luminally fed group, whereas the "apparent" Km was similar in all groups. Diversion of the pancreaticobility secretions did not affect glucose uptake in luminally fed or TPN-fed animals. TPN-fed and fasted animals had similar glucose uptake. Luminal feeding did not have a remote effect on glucose uptake in intestine isolated from the nutrient stream. The results indicate that luminal nutrients maintain carrier-mediated glucose transport after direct contact with the mucosa. Overall metabolic balance and pancreaticobiliary secretions do not affect carrier-mediated glucose transport. The nutrient effect appears to involve an increased number of glucose carriers per cell without a change in carrier affinity for glucose.

Animals↗
PubMed1980

pH dependence of micellar diffusion and dissociation.

A simplified model system was used to examine the effect of pH on the diffusion and dissociation of mixed micelles across an interphase. Diffusion of radioactively labeled taurocholate and oleic acid from a micellar solution into a phosphate buffer of varying pH (5.0-8.0) was measured. The proportion of bile salt and fatty acid as monomers and aggregates in both solutions was determined by ultrafiltration. Results indicate that all of the oleic acid existed as aggregates in the micellar solution, whereas taurocholate was in equilibrium between aggregate and monomer forms. Between pH 5.0 and 7.0, oleic acid and taurocholate diffusion was inversely related to pH and due to the differences in aggregate but not monomer diffusion. Fatty acid diffusion across the interface was always less than taurocholate diffusion, because taurocholate monomers could also diffuse across the interphase. Calculation of the proportion of taurocholate diffusion from aggregate and monomers based on micellar composition was similar to measured values at pH greater than or equal to 6.5, indicating a lack of micelle dissociation. However, at pH less than or equal to 6 measured values for bile salt monomers exceeded calculations, indicating that a low pH microclimate favors dissociation of micelles. A hypothesis is advanced to explain these events occurring in a disequilibrium area adjacent to the epithelial cell membrane.

Colloids↗
PubMed1979

Delayed esophageal perforation after pneumatic dilatation for the treatment of achalasia.

Two cases of delayed esophageal perforation following a pneumatic dilatation for the treatment of achalasia are presented. Esophagrams obtained immediately after pneumatic dilatation failed to reveal a perforation. Increasing symptoms prompted repeat contrast studies, at which time an esophageal perforation was demonstrated. The occurrence of delayed esophageal perforation after pneumatic intrumentation is emphasized. An ischemic etiology for this delayed perforation is postulated.

Dilatation↗