PubMed Health⌕ Search

Biomedical subjects

Y F Shiau

Publications and source records attributed to Y F Shiau.

29 records · Page 2Linked to original sources
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 insulin on in vitro intestinal fatty acid esterification in the rat.

We have previously shown that glucose metabolism plays an important role in modifying intestinal fatty acid esterification. Because it is well known that glucose metabolism is under insulin regulation, we examined the effect of insulin on intestinal fatty acid esterification. Insulin pretreatment led to a marked decrease in in vitro intestinal fatty acid esterification, but this decrease was abolished by maintaining blood glucose above 80 mg/dl. Addition of insulin to the incubation medium failed to produce any effect on intestinal fatty acid esterification. The decreased fatty acid esterification on hypoglycemic rats was not associated with changes in fatty acid uptake or lipid esterifying enzyme activities. However, there was a significant increase in the production of volatile metabolites of fatty acid. We conclude that 1) insulin itself has no effect on intestinal fatty acid esterification, 2) the effects observed in this study are due to insulin-induced hypoglycemia, 3) hypoglycemia does not alter intestinal fatty acid uptake or intrinsic esterification activity, but leads to preferential oxidation rather than esterification of fatty acid by the small intestine, and 4) the critical blood glucose concentration needed to maintain normal esterification in the rat was approximately at 80 mg/dl.

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↗
PubMed1980

Apical distribution of fatty acid esterification capacity along the villus-crypt unit of rat jejunum.

Distribution of fatty acid esterification capacity along the structure of the villus-crypt unit was studied in both in vivo perfused an in vitro incubated rat jejunum. Using a cryostat sectioning technique, the intestine was sectioned transversely at 6 micron thickness, from the tip of the villus to the crypt. Morphology and sucrase activity were used as markers to define the location along the villus-crypt unit. Fatty acid esterification capacity was found to be more apically concentrated in both in vivo and in vitro preparations. The apical distribution of fatty acid esterification capacity is a reflection of the distribution patterns of lipid esterifying enzyme activity along the villus-crypt units.

1-Acylglycerol-3-Phosphate O-Acyltransferase↗
PubMed1979

Development of fatty acid esterification mechanisms in rat small intestine.

Fatty acid esterification was measured in fetal jejunal and ileal isografts implanted under the kidney capsules of adult host rats and compared to the age-controlled intestine grown in situ. Studies were conducted on the 21st, 35th, 49th, and 63rd postconceptional days, corresponding to prenatal, suckling, weaning, and weaned rats. Substantial fatty acid esterification activity was found in prenatal jejunum but not in ileum. A proximal-distal gradient of fatty acid esterification was observed in all groups grown in situ, but not in isografts. The monoglyceride pathway (MG-P) accounted for about one-third of total fatty acid esterification (TFAE) in jejunum grown in situ and remained constant through the study. In the ileum, MG-P was the major esterification pathway during the first 4 postnatal weeks, but decreased progressively after weaning to become insignificant in adult rats. TFAE fell in the jejunal isografts, whereas it increased in the ileum. MG-P remained as the major pathway in the implanted jejunum and ileum. Our studies suggest that luminal contents are probably the most important modulator for the development and maintenance of intestinal fatty acid esterification, and "fetal programming" manifested by changes in fatty acid esterification mechanisms in the isografts is less important.

Animals↗
PubMed1978

Effect of sugar and monoglyceride on fatty acid esterification.

The effect of hexose and monoolein on fatty acid esterification was studied in everted rings of rat jejunum. By use of [3H]oleic acid and [U-14C]glucose, esterification via both phosphatidic acid and monoglyceride pathways was quantified. Our results showed that 1) metabolizable sugars stimulate fatty acids esterification regardless of their mode of transport; 2) in the presence of glucose alone, in vitro fatty acid esterification is mediated entirely by the phosphatidic acid pathway; 3) glucose stimulates both esterification pathways in the presence of monoolein; 4) monoolein stimulates only the monoglyceride pathway and has no effect on the phosphatidic acid pathway; and 5) the rate-limiting factor in the presence of monoolein alone is the formation of acyl-CoA, whereas in the presence of glucose alone, the rate-limiting factor is the formation of alpha-glycerophosphate.

Acyl Coenzyme A↗
PubMed1974

Intestinal transport of weak electrolytes. Evidence in favor of a three-compartment system.

A study has been made of the transmural fluxes of benzoic, phenylacetic, and pentanoic acids, benzylamine, hexylamine, and D-amphetamine across rat jejunum incubated in vitro. The M to S fluxes of the weak acids were greater than their corresponding S to M fluxes, and the S to M fluxes of the weak bases were larger than their M to S fluxes. These patterns of asymmetric movements were observed when the transmural electrical potential difference was clamped at 0 mV, and when the pH values of the mucosal and serosal fluids were identical. The effects of a weak acid on the fluxes of other weak electrolytes were qualitatively similar when the effector weak acid was added to the mucosal fluid, and when it was added to the serosal fluid. But the effects of a weak base on the fluxes of other weak electrolytes were dependent upon its location, and the interactions observed when the effector weak base was added to the mucosal fluid were qualitatively different than those seen when it was added to the serosal fluid. The interactions between weak electrolytes could readily be explained in terms of the function of a system of three compartments in series, in which the pH of the intermediate compartment is greater than that of the bulk phases. But these observations could not be explained in terms of an analogous system involving an intermediate compartment of low pH, or in terms of a carrier mediated system. The transport function of the three-compartment system can be described in the form of an equation, and it is found that a pH difference of less than 0.5 unit may explain our observations on weak electrolyte transport.

Amines↗