Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Absorption”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,297 records · Page 72Linked to original sources
PubMed1978

Chylomicron apoprotein localization within rat intestinal epithelium: studies of normal and impaired lipid absorption.

Monospecific antisera were produced to two chylomicron apoproteins (apoB, apoA-I) and utilized for indirect immunofluorescent localization of these apoproteins within rat intestinal epithelium during normal and impaired lipid absorption. Isolated intestinal epithelial cells prepared after different periods of lipid absorption from in situ intestinal segments revealed a rapid increase in fluorescence for both apoproteins that filled the entire apical portion of the cell. Prolonged lipid absorption for as long as 5 hr demonstrated sustained immunofluorescence and gave no indication of a depletion of the intestinal mucosa for either apoprotein during normal lipid absorption. [(3)H]Leucine incorporation into mesenteric lymph chylomicron apoproteins showed a linear decrease in specific activity of total chylomicron protein as well as apoB over 4 hr of a continuous lipid infusion indicating sustained active apoprotein synthesis during prolonged lipid absorption. Acetoxycloheximide, a potent inhibitor of protein synthesis, was employed to determine the dynamics of chylomicron apoproteins during an experimental condition of impaired lipid absorption. In animals with inhibited protein synthesis, fluorescence for both apoproteins was present early in the course of lipid absorption; however, at 60 min after the onset of lipid absorption, fluorescence for both apoproteins was absent. Fluorescence for both apoproteins returned during the recovery of protein synthesis. The present studies have confirmed previous results that localized two chylomicron apoproteins within intestinal epithelial cells. The present studies extend these observations and disclose a rapid and sustained synthesis of these apoproteins during prolonged chylomicron formation. During an experimental condition of impaired protein synthesis there was a marked reduction in the mucosal content of both apoA-I and apoB. These results are the first demonstration of impaired mucosal apoprotein synthesis during an experimental model of impaired lipid absorption.

Animals↗
PubMed1990

Small-bowel origin of the signal for meal-induced jejunal absorption.

A meal stimulates the absorption of water and electrolytes from the proximal jejunal lumen. Neither sham feeding nor gastric distention alters this meal-induced jejunal absorption, implying no role for the cephalic or gastric phases of digestion. This study tested the hypothesis that the small bowel is the origin of the proabsorptive signal for meal-induced jejunal absorption. Twenty-five-centimeter canine proximal jejunal Thiry-Vella fistulas were constructed, and chronic duodenal catheters were placed. Jejunal absorption studies (n = 72) were performed by luminal perfusion of the jejunal segments with an isotonic buffer containing radioactive carbon-labeled polyethylene glycol. Each study consisted of a 1-hour basal period followed by a 3-hour experimental period. Ten groups were studied: control, orally ingested mixed meal, and 600 ml duodenal infusions of either water, saline solution, protein, lipid, carbohydrate, 150 mmol/L mannitol, 300 mmol/L mannitol, or 600 mmol/L mannitol, each delivered at 10 ml/min over 60 minutes. The control, water, and saline solution groups showed no significant changes in integrated 3-hour jejunal absorption above basal. The ingested mixed meal significantly increased water and electrolyte absorption (p less than 0.0001). The isovolumetric, isocaloric duodenal nutrient infusions of protein, lipid, and carbohydrate all significantly increased jejunal water and electrolyte absorption (p less than 0.0001). The poorly absorbed solute mannitol significantly increased absorption (p less than 0.0001) in a dose-dependent fashion. These results indicate that the proabsorptive signal for meal-induced jejunal absorption originates from or distal to the duodenum. This newly defined enteroenteric response occurs independently of nutrient composition and responds to increasing osmolarity of poorly absorbed solutes such as mannitol.

Absorption↗
PubMed1990

Use of the paracellular way for the intestinal absorption of sugars.

Passive absorption of D-Galactose (in the presence of 0.5 mM phlorizin), 2-deoxy-D-glucose and D-Mannitol by rat jejunum has been measured in vivo by perfusion of an intestinal segment with recirculation, along successive absorption periods of 5 or 10 min duration. In the range of 1 to 40 mM concentrations, the three solutes were absorbed at a very similar rate that varied as a lineal function of the concentrations in the perfusion solution. Absorption of 1 mM solute was not modified by the presence of 40 mM glucose or galactose. Passive absorption kinetics suggests processes of simple diffusion or solvent drag. The use of paracellular way for the passive absorption is supported by the fact that triaminopyrimidine (TAP) and protamine, which decrease the permeability through the tight junctions, also inhibit the absorption, with similar characteristics for both actions: TAP inhibition (53%) is very rapid and can be easily reversed, while that of protamine (30%) requires some time of previous exposure, lasts longer and can be reversed by heparin. The same analogy is shown by two actions that enhance the paracellular permeability: theophylline increases (30%) the passive absorption with lasting effect, while luminal hypertony enhances absorption transitorily. The passive absorption of the assayed solutes could be estimated to take place by the paracellular way in at least 50% and probably 70% or even more. The measure of net fluid fluxes reveals that solute fluxes must be prevailingly explained by simple diffusion, as the solvent drag can only play a very minor role.

Animals↗
PubMed1989

[Studies on the absorption kinetics of subcutaneously administered insulin].

This study was designed to evaluate, using compartmental model analysis, the effects of jet injection, changes in injected dosage, and mixture of short- and intermediate-acting insulin preparations on the absorption kinetics of human insulin (HI) mainly in rabbits. The following results were obtained. (1) It was found that a split-pool model was adequate for the evaluation of the absorption kinetics of insulin. (2) Jet injection resulted in more rapid absorption of insulin than needle injection. Since parameter K12 (inter-pool rate constant) of jet injection was three times as large as that of needle injection, the accelerated absorption by jet injector could result from the rapid movement of insulin from the injection site to the absorption site. (3) A negative correlation between insulin dosage and Kd (degradation rate constant) was observed, suggesting that the process of subcutaneous absorption of insulin includes a nonlinear component. (4) The prompt injection of Actrapid HI mixed with Monotard HI in a single syringe caused a delayed absorption of Actrapid HI. In contrast, there was no prolonged absorption after the injection of regular HI mixed with NPH-HI in a single syringe. There was a significant positive correlation between the percent change of K12 (in separate injection and mixed injection) in vivo and the recovery rate of short-acting insulin when mixed with intermediate-acting insulin in vitro. In clinical studies of diabetic subjects, higher serum free insulin levels before noon and higher K12 values were observed after the mixed injection of regular HI and NPH-HI, compared with that of Actrapid HI and Monotard HI. These results suggest that the application of compartmental model analysis is useful to studying the absorption kinetics of subcutaneously injected insulin.

Adult↗
PubMed1986

Effects of some carbohydrates on iron absorption.

Two experiments were performed to examine the effects of various carbohydrates (fructose, lactose, corn starch, wheat starch and potato starch) on the utilization of iron, on Fe-depleted rats. These received a single meal that contained the test carbohydrate at a 60% level, labelled with 59Fe. The rest of the experiment the rats were fed a diet which contained glucose at a 60% level as the carbohydrate source. In both experiments rats were fasted overnight, and the dose was offered in the form of a morning meal. To assay for 59Fe, the animals were counted in a "Whole body counter" between two and four hours after dosing, and every day for the following 10 days. Percentage retention and absorption, as well as hemoglobin values were determined. In the first experiment, the replacement of glucose by fructose at a 60% level enhanced significantly iron absorption and retention. An increase in absorption and retention also occurred when glucose was replaced by lactose at a 60% level, but the difference was not statistically significant. Administration of 59Fe as an 59Fe-fructose chelate did not seem to have a significant effect on retention and absorption when compared to the effect of dosing with 59Fe adsorbed onto a fructose diet. This not rule out the possibility that chelation is the mechanism responsible for the enhancing effect of fructose on iron utilization. The complex could have been formed in the stomach, resulting in a significant absorption for both the 59Fe-labelled meal and the 59Fe-carbohydrate complex-labelled meal. In the second experiment, administration of a meal that contained either of the starches resulted in a reduction on retention and absorption of 59Fe. The decrease, however, was statistically significant only for cooked corn starch, wheat starch and cooked wheat starch. The effect of cooking was to reduce even more the retention and absorption of 59Fe, but this reduction was statistically significant only for corn starch. The depressing effects of starches on iron retention and absorption are quite relevant to human nutrition. In the developing countries, diets are generally high in cereal products - often whole grain cereals - and low in animal products. The inhibitory effects of cereals on iron absorption have been traditionally attributed to the presence of phytates and fiber, but the data herein presented suggest that high intakes of starches may be inhibitory as well.

Absorption↗
PubMed1969

Inhibition of lymphatic absorption of cholesterol by cholestane-3 beta, 5 alpha, 6 beta-triol.

The effect of cholestane-3,5alpha,6-triol (CT) on the intestinal absorption of cholesterol and oleic acid, as well as the absorption of labeled CT, was studied in lymph ductcannulated rats. Intragastric administration of 50 mg of CT in an emulsion with cholesterol-7alpha-(3)H and oleic acid-1-(14)C resulted in 50% inhibition of sterol transfer into lymph but only 8% depression of fatty acid absorption over an 8 hr period. The absorption of labeled CT into lymph was only 2-3% compared with 50% absorption of cholesterol when each was fed alone. 10% of the fed CT was recovered in the intestinal mucosa, and of this, one-half was associated with the brush border fraction. In rats fed CT 6 days prior to cholesterol and fatty acid administration, there was no effect on fatty acid absorption, while cholesterol absorption was reduced by almost 30%. When the intestinal mucosa from these animals were investigated by electron microscopy, it appeared that CT feeding resulted in numerous enlarged mitochondria and a marked increase in length of the microvilli. If animals were allowed to recover for 6 days from the CT prefeeding regime, the intestinal mucosa appeared normal, and the absorption of cholesterol approached that in controls. A possible mechanism for CT inhibition of cholesterol absorption was shown to be competition for the enzyme cholesterol esterase which esterifies cholesterol prior to entrance into the lymphatic system. CT itself is poorly esterified and poorly absorbed, but it is effective in inhibiting esterification of cholesterol in vitro.

Animals↗
PubMed1983

Portal hemodynamics, intestinal absorption, and postshunt encephalopathy.

Although total diversion of portal blood flow has been considered to be the main factor leading to encephalopathy following nonselective shunt (NSS), increased intestinal absorption of cerebral toxins secondary to mesenteric venous decompression could also play a role. Conversely, the low frequency of encephalopathy after the distal splenorenal shunt (DSRS) may be due to preservation of both hepatic portal perfusion and mesenteric venous hypertension. Portal hemodynamics, intestinal absorption of D-xylose, ammonia metabolism, and clinical encephalopathy were assessed preoperatively and in the early and late postoperative periods in cirrhotic patients selected for the DSRS (n = 12) and NSS (n = 10). Preoperatively, NSS patients had significantly less hepatopetal portal blood flow (P = 0.03) and lower D-xylose absorption (P = 0.004) than DSRS patients. DSRS resulted in no significant alterations in hepatic portal perfusion, portal pressure, D-xylose absorption, fasting blood ammonia (NH3), or tolerance to an oral dose of ammonium chloride. In contrast, NSS resulted in complete portal diversion and decompression and significant enhancement of D-xylose absorption on both the early (P = 0.02) and late (P = 0.03) postoperative evaluations. Early and late postoperative levels of MH3 were significantly higher in NSS patients. Encephalopathy was more frequent after NSS (80%) than after DSRS (17%, P = 0.003). When all patients were considered, preoperative to early DSRS (17%, P = 0.003). When all patients were considered, preoperative to early postoperative change in NH3 correlated with change in D-xylose absorption (r = 0.52, p = 0.02), and there were significantly more individuals with a greater than 2 gm increase in D-xylose absorption who developed encephalopathy (83%) than patients with no or minimal increase in D-xylose absorption (33%, P = 0.04). The results of this study suggest that altered intestinal absorption may be one of many factors determining postshunt cerebral function.

Ammonia↗
PubMed1981

Cholesterol absorption in cirrhosis: the role of total and individual bile acid pool size.

Dietary cholesterol absorption was studied in patients with either "mild" (n = 23) or "severe" (n = 12) liver cirrhosis in relation to both total and individual bile acid pool size. Cholesterol absorption was significantly reduced in both groups of patients, and it was inversely related (r = -0.68; p less than 0.001) to the severity of the disease. Total, cholic acid, and deoxycholic acid p ool sizes were significantly reduced in cirrhosis, and a correlation was found between cholesterol absorption and cholic acid pool size (r = 0.78; p less than 0.001). In 5 patients, cholesterol absorption and bile acid pool size were estimated both before and after treatment with cholic acid (15 mg/kg/day) plus ampicillin (2 g/day). The treatment was followed by a mean threefold increase of cholic acid pool and by a sharp enhancement of cholesterol absorption in each patient. In conclusion, cholesterol absorption is often impaired in cirrhosis and is related to the severity of the disease. The correlation between cholic acid pool and cholesterol absorption and the constant increase of the absorption values after cholic acid pool expansion suggest that the size of cholic acid pool may be considered as an important factor in the regulation of cholesterol absorption.

Adult↗
PubMed1981

Bile salt-enhanced rat jejunal absorption of a macromolecular tracer.

Bile salt deconjugation may occur in the jejunum under conditions of fecal colonic overgrowth of the small intestine. We studied the effects of conjugated and deconjugated bile salts on rat jejunal absorption of a macromolecular tracer, horseradish peroxidase, in an in vivo perfusion system. At a 0.5 mM perfusion concentration, only the deconjugated bile salts, cholate and deoxycholate, produced a significant increase in horseradish peroxidase absorption into serum. At a 0.5 mM concentration of the conjugated salt, taurocholate, horseradish peroxidase-absorption was indistinguishable from that seen in bile salt-free preparations. At a higher 5 mM concentration, both the conjugated and deconjugated salts increased jejunal HRP absorption into serum over that seen in bile salt-free preparations; this absorption wa most marked with the deconjugated salts. At a 0.5 mM level, the bile salts induced minimal sodium and glucose transport alterations but did not produce evidence of morphologic damage to villi or absorptive epithelial cell organelles. At a 5 mM level, the deconjugated salts induced glucose and sodium transport abnormalities and appeared to damage cellular organelles. Our observations suggest that an alteration in the tight junctional barrier to macromolecular absorption may play a role in some of the enhanced horseradish peroxidase absorption seen with deoxycholic acid in these experiments. The process of an increased absorption of intact macromolecules induced by products of bacterial metabolism may be of pathologic significance in the etiology of immunologically related intestinal disease or in toxigenic processes.

Animals↗
PubMed1977

Determination of cholesterol absorption in man by intestinal perfusion.

In this study a technique is described for estimating net absorption of total cholesterol (endogenous + exogenous) that enters the intestine. The method employs intubation of patients with a 3-lumen tube that contains a 10-cm mixing segment in the duodenum and a 100-cm absorption segment in the jejunum. A liquid formula diet containing varying amounts of exogenous cholesterol is infused continuously into the upper duodenum for a period of several hours; the formula diet stimulates constant contraction of the gallbladder and thus provides for continous secretion of biliary cholesterol sitosterol as a marker, the input of endogenous + exogenous cholesterol can be measured at the end of the 10-cm mixing segment. Net cholesterol absorption is estimated from the disappearance of cholesterol relative to beta-sitosterol over the next 100-cm of jejunum. When radioactive cholesterol was also used as a marker, radioactivity usually disappeared more rapidly than the mass of choleesterol over the absorption segment; this suggests that a significant amount of isotope exchange occurs in the upper intestine. Using beta-sitosterol as a marker, the extent of exchange can be determined. In six patients, cholesterol inputs ranged from 51 to 118 mg/hr, and net percentage absorption was 34-56%. When inputs of cholesterol were acutely increased by enhancing exogenous cholesterol, absolute absorption was uniformly increased, but percentage absorption either remained the same or was decreased somewhat. Changine inputs of beta-sitosterol had a striking effect on cholesterol absorption, and relatively small increments of beta-sitosterol almost always produced corresponding reductions in uptake of cholesterol. The intestinal perfusion method appears to provide certain advantages over previous techniques for estimating total cholesterol entering the upper intestine, including that derived from both endogenous and exogenous sources. Measurements can be made over short periods of time, and the method allows for determination of effects of acute changes in the intestinal milieu on cholesterol absorption. Finally, the technique defines the extent of isotope exchange between cholesterol in the intestinal mucosa and in the lumen.

Adult↗
PubMed1993

Pharmacologic consequences of cholesterol absorption inhibition: alteration in cholesterol metabolism and reduction in plasma cholesterol concentration induced by the synthetic saponin beta-tigogenin cellobioside (CP-88818; tiqueside).

Natural and synthetic saponins inhibit cholesterol absorption and reduce plasma cholesterol levels in experimental animals and are therefore of potential pharmacologic utility in the treatment of hypercholesterolemia. To determine the effects of this class of compounds on cholesterol absorption and metabolism, we evaluated the effects of the synthetic saponin, beta-tigogenin cellobioside (tiqueside; CP-88818), on male golden Syrian hamsters. When administered as either a single oral bolus or as a dietary supplement for up to 2 weeks, tiqueside inhibited cholesterol absorption in a dose-dependent manner in both the presence and absence of dietary cholesterol. Administration of tiqueside to chow-fed hamsters as a 0.2% dietary supplement (150 mg/kg per day) for 4 days resulted in a 68% decrease in intestinal cholesterol absorption with no change in either bile absorption or cholesterol 7 alpha-hydroxylase activity, suggesting that tiqueside inhibits cholesterol absorption without interfering with enterohepatic bile acid recirculation. Under these conditions, hepatic cholesterol levels were also reduced in a dose-dependent manner. Hepatic cholesterol reduction was highly correlated with cholesterol absorption inhibition, and induced compensatory increases in both hepatic HMG-CoA reductase activity and hepatic low density lipoprotein (LDL) receptor levels. Compensatory increases in intestinal HMG-CoA reductase activity were also noted after tiqueside administration, and are consistent with a luminal mechanism for tiqueside action. As a consequence of these changes to cholesterol metabolism, tiqueside administration induced plasma cholesterol reductions that were highly correlated with both hepatic cholesterol reduction and cholesterol absorption inhibition. Tiqueside also produced comparable plasma cholesterol lowering in a variety of other species fed either cholesterol-free diets (hamster, rat, mouse, dog) or cholesterol-containing diets (hamster, rat, rabbit, mouse, cynomolgus monkey, rhesus monkey, SEA quail) indicating the ubiquity of tiqueside action. For all species evaluated except the dog, the reduction in plasma cholesterol was due primarily to a reduction in circulating non-HDL cholesterol levels with little or no change in HDL cholesterol levels. Taken together, these results indicate that inhibition of cholesterol absorption by tiqueside produces profound effects on cholesterol metabolism without affecting bile acid metabolism, and that these changes lead to reductions primarily in plasma non-HDL cholesterol concentrations. The synthetic saponin, tiqueside, may thus represent a prototypical form of therapy for the treatment of hypercholesterolemia.

Amino Acid Sequence↗
PubMed1995

Evaluation of the use of beta-sitostanol as a nonabsorbable marker for quantifying cholesterol absorption.

For over a decade investigators have quantified cholesterol absorption by comparison of dietary intake and fecal excretion of isotopic cholesterol with that of beta-sitosterol as a "nonabsorbable" marker. However, beta-sitosterol might not be ideal due to its potential for absorption. We therefore carried out two studies to evaluate a new marker with less potential for absorption, [3H]beta-sitostanol. In the first study (Study I, n = 22), we compared absorption of [3H]beta-sitostanol and [14C]beta-sitosterol in a simultaneous dual-label continuous feeding ("phytosterol absorption") experiment. We observed a consistently higher ratio of [3H]beta-sitostanol/[14C]beta-sitosterol in the stool relative to diet on the first day of fecal collection (6.1% +/- 3.2% loss of [3H]beta-sitosterol, range 3-12%), but thereafter, the ratio in stool was similar to that in diet. In Study II (n = 23), we compared cholesterol absorption directly using [3H]beta-sitosterol and [14C]cholesterol, and, separately, [3H]beta-sitostanol and [14C]cholesterol. We found that mean absorption between the two methods was similar (45% +/- 11% versus 44% +/- 10%, respectively, P difference = 0.40), and the two methods correlated well with one another (r = 0.83) when samples from all available days were used. Variability between the two methods was greater in individuals who absorbed more than 40% of cholesterol. Cholesterol loss on day 2 estimated from use of beta-sitostanol as a nonabsorbable marker was predictive of absorption using ratios from days 4-6 (r = 0.80). These results suggest that, for the majority of subjects, beta-sitosterol is a valid nonabsorbable marker for cholesterol absorption.

Adult↗
PubMed1997

Effect of source of iron on duodenal absorption of iron, calcium, phosphorous, magnesium, copper and zinc in rats with ferropoenic anaemia.

We studied the effects of iron deficiency on the in vivo absorption (by using the intestinal perfusion technique in the duodenum) of different dietary sources of iron (haem, non-haem and equal parts of both forms) and investigated the interactions between iron and calcium, phosphorous, magnesium, copper and zinc in control and iron-deficient rats. Three perfusion solutions containing a different source of iron were used: solution 1, ferric citrate; solution 2, haemoglobin; solution 3, equal parts of ferric citrate and haemoglobin. We also tested the same perfusion solution with 2,4-dinitrophenol (2,4-DNP), an inhibitor or oxidative phosphorylation (solutions 1-I, 2-I and 3-I). In control rats we observed three mechanisms of iron absorption: passive for soluble iron salts, active receptor-mediated for non-haem iron complexes, and active receptor-mediated for haem iron. In anaemic rats iron absorption was greater than in controls, except after perfusion with solution 2 (containing haemoglobin). Absorption increased as a result of both the passive and active, receptor-mediated mechanism for non-haem iron complexes. The active component was influenced by the depletion of haem receptors under severe iron deficiency. The absorption of calcium, copper and zinc in iron-deficient animals was lower than in controls, whereas phosphorus and magnesium absorption were not significantly affected. After perfusion with solution 2 or 3, calcium, copper and zinc absorption were lower than after solution 1. We conclude that ferropoenic anaemia in the rat impairs the absorptive process of those minerals that are absorbed, at the duodenal level mainly via active transport (haem iron, calcium, copper and zinc), but does not affect the active component involved in non-haem iron absorption.

Anemia, Iron-Deficiency↗
PubMed2004

In vitro dissolution and in vivo oral absorption of methylphenidate from a bimodal release formulation in healthy volunteers.

PURPOSE: The objective of this study was to evaluate the in vitro dissolution and in vivo absorption of D,L-threo-methylphenidate (MPH) from a novel bimodal release formulation (Ritalin LA capsule) compared with an immediate-release formulation (Ritalin IR tablet) in healthy volunteers. METHODS: The bimodal release formulation contains 50% of the dose in the immediate-release (IR) beads and 50% in polymethacrylate-coated, delayed-release (DR) beads. To better understand the impact of dissolution from the DR beads on oral absorption of MPH, three Ritalin LA formulations with different dissolution profiles for the DR beads (referred to as slow-, medium and fast-release formulations) were prepared, and tested together with the immediate-release formulation in 18 healthy male and female volunteers after a single oral dose under fasted conditions. The rate and extent of oral absorption of MPH were evaluated based on the overall Cmax, tmax and AUC values, as well as the Cmax, tmax and AUC values for each individual peak of the bimodal plasma concentration-time profile. The in vivo absorption-time profile was also examined by deconvolution. RESULTS: All three Ritalin LA formulations demonstrated similar bimodal plasma concentration-time profiles with two peak concentrations observed at approximately 2 and approximately 6 h post dose, mimicking that of Ritalin IR tablets given 4 h apart. Deconvolution results showed that the absorption of MPH was biphasic, with a rapid absorption phase between 0 to approximately 2 h, and a somewhat slower second absorption between approximately 3-6 h, consistent with the in vitro bimodal release characteristics of Ritalin LA formulation. The three Ritalin LA formulations were bioequivalent to one another based on the overall Cmax and AUC values and the corresponding values describing the first and second peaks, although their in vitro dissolution profiles for the DR beads were different. Compared with Ritalin IR, the Ritalin LA formulation demonstrated a similar rate of absorption for the first peak, a lower second Cmax and a higher trough concentration between peaks, as well as similar overall plasma AUC. CONCLUSIONS: Following a single oral drug administration, Ritalin LA demonstrated a two-peak plasma concentration-time profile, similar to that of the IR formulation given 4 h apart, but with less fluctuation in the plasma concentration-time profile. The in vivo biphasic absorption of MPH appeared to be well correlated with the bimodal dissolution characteristics of this new Ritalin LA formulation, and some changes in the dissolution profiles for the DR beads appeared not to affect the overall bioavailability of MPH in humans.

Administration, Oral↗
PubMed1999

Decreased cerebrospinal fluid absorption during abdominal insufflation.

BACKGROUND: Intracranial pressure (ICP) is known to rise during induced CO(2) pneumoperitoneum. This rise correlates with an increase in inferior vena caval pressure; therefore, it is probably associated with increased pressure in the lumbar venous plexus. Branches of this plexus communicate with arachnoid villi in the lumbar cistern and the dural sleeves of spinal nerve roots-areas where cerebrospinal fluid (CSF) absorption to normally takes place. The increased venous pressure in this area may impede CSF absorption. Because CSF is produced at a constant rate, decreased absorption will increase ICP. We hypothesized that increased ICP occurring during abdominal insufflation is due, at least in part, to decreased absorption of CSF. The purpose of this study is to show that CSF absorption is inhibited during abdominal insufflation. METHODS: After appropriate approval was obtained, 16 domestic swine were anesthetized and injected into the CSF with 100 microcuries (microCu) of I(131) radioactive iodinated human serum albumin (RISA) in 2 ml of normal saline. Eight subjects underwent CO(2) abdominal insufflation to 15 mmHg and were maintained for 4 h. A control group did not undergo insufflation. Blood levels of RISA were measured over a 4-h period to determine the rate of CSF absorption. RESULTS: Blood levels of RISA increased at a slower rate in the subjects undergoing abdominal insufflation than in the control group. The mean change over 2 h in the insufflated group was 15% compared to 34% in the control group (p = 0.02). This difference indicates decreased absorption of CSF in the insufflated group. CONCLUSIONS: These results demonstrate decreased absorption of CSF during abdominal insufflation and support the hypothesis that the increase in ICP pressure occurring during abdominal insufflation is caused, at least in part, by decreased absorption of CSF in the region of the lumbar cistern and the dural sleeves of spinal nerve roots.

Animals↗
PubMed1990

Factor analysis of the near-ultraviolet absorption spectrum of plastocyanin using bilinear, trilinear, and quadrilinear models.

Factor analysis was used to resolve the spectral components in the near-uv absorption spectrum of plastocyanin. The data set was absorption as a function of four variables: wavelength, species of plastocyanin, oxidation state of the copper center, and environmental pH. The data were fit with the traditional bilinear model, as well as with trilinear and quadrilinear models. Trilinear and quadrilinear models have the advantage that they uniquely define the components, avoiding the indeterminacy of bilinear models. Bilinear analysis using the absorption spectra of tyrosine and copper metallothionein as targets resulted in a two-component solution which was nearly identical to that obtained using trilinear and quadrilinear models, for which no targets are required. The two-component models separate the absorption into tyrosine and copper center components. The absorption of tyrosine is found to be pH dependent in reduced plastocyanin, and the absorption magnitude of the reduced copper center is the same in the four different plastocyanin species. Further resolution is provided by a three-component quadrilinear model. The results indicate that there are at least two different electronic transitions which cause the absorption of the reduced copper center and that one of them couples to a tyrosine residue. It is the absorption of this coupled tyrosine residue which is pH dependent. Correlation of the results with previous studies indicates that it is Tyr 83 which is the perturbed residue. The separation of the absorption of the copper center and Tyr 83 provides spectroscopic probes for the conformations of the north pole and east face reaction sites on the plastocyanin protein.

Binding Sites↗
PubMed1987

Thiazides stimulate calcium absorption in urinary bladder of winter flounder.

Thiazides inhibit voltage-independent NaCl absorption in the urinary bladder of the winter flounder presumably by blocking an electroneutral mucosal Na/Cl co-transporter. As thiazides stimulate calcium absorption in mammalian distal convoluted tubule while inhibiting NaCl absorption, we studied the effects of hydrochlorothiazide (HCTZ) on unidirectional 45Ca fluxes and intracellular electrical potential in short-circuited bladders to examine possible mechanisms of HCTZ effects on calcium transport. Basal secretory calcium flux was, on average, slightly larger than absorptive flux, reflecting small net calcium secretion. Mucosal addition of HCTZ (10(-4) M) stimulated absorptive calcium flux by 46% while the secretory flux was unaltered. Thus, HCTZ tended to induce net calcium absorption. Pre-treatment with serosal ouabain (10(-4) M) attenuated the HCTZ-induced increase in absorptive calcium flux. Moreover, HCTZ hyperpolarized the mucosal membrane potential by 18% as measured by conventional open-tip microelectrodes. These effects of HCTZ are consistent with the hypothesis that HCTZ indirectly stimulates Na/Ca exchange located at the serosal membrane. In conclusion, HCTZ in flounder urinary bladder, as in mammalian distal convoluted tubule, simultaneously inhibits NaCl absorption and stimulates calcium absorption. This study expands on the functional similarities between the flounder urinary bladder and the mammalian distal convoluted tubule.

Animals↗
PubMed1981

Fourier transform infrared absorption studies on the sulfhydryl groups in heavy meromyosin.

Infrared absorptions of heavy meromyosin solutions were studied in the frequency range of 2600 cm-1 to 1800 cm-1 with a Fourier transform infrared spectrophotometer. An absorption band characteristic of the stretching vibration of sulfhydryl groups was found at about 2565 cm-1. By comparison with the infrared absorption spectrum of a cysteine solution, the absorption band of sulfhydryl groups in heavy meromyosin showed that the absorption intensity is much stronger, the absorption peak shifts to a lower wavenumber and the width of the absorption band is much broadened. These results indicate that the sulfhydryl groups in heavy meromyosin are strongly hydrogen-bound. The additions of ATP and ADP increased the absorption intensity of the absorption band, suggesting the that hydrogen-bonded structure involving the sulfhydryl groups becomes more strengthened on the binding of ATP and ADP. This indicates that myosin heads change conformation around the sulfhydryl groups during ATP hydrolysis.

Adenosine Diphosphate↗