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PubMed1996

In vivo lactose digestion in preterm infants.

In vitro studies of intestinal lactase activity and breath-hydrogen studies have suggested that the capacity for lactose digestion in preterm infants is less than the usual intake. To explore this question using an in vivo approach, we determined the fraction of dietary lactose hydrolyzed to glucose (and galactose) in 14 preterm infants with a gestational age of 26-31 wk at the time of birth but a postconceptional age of 31-37 wk at the time of study. The percentage of lactose digested was estimated after 6-h, primed, constant gastric infusions of [1-(13)C]glucose and D-[-1-(13)C]lactose on alternate days. A coefficient of lactose fermentation was derived from the rates of pulmonary excretion of hydrogen and carbon dioxide. Mean (+/- SD) lactose digestion was 79 +/- 26%. There was a significant inverse rank (r = -0.799, P < 0.01) and linear (r = -0.587, P < 0.05) correlation between this variable and postconceptional age. The percentage of lactose fermented averaged 35 +/- 27%.

Carbon Isotopes↗
PubMed2000

Chronic consumption of fresh but not heated yogurt improves breath-hydrogen status and short-chain fatty acid profiles: a controlled study in healthy men with or without lactose maldigestion.

BACKGROUND: Ingestion of fermented dairy products induces changes in the equilibrium and metabolism of the intestinal microflora and may thus have beneficial effects on the host. OBJECTIVE: We compared the effects of chronic consumption of yogurt with (fresh) or without (heated) live bacterial cultures (Lactobacillus bulgaricus and Streptococcus thermophilus) on plasma glucose, insulin, triacylglycerols, cholesterol, fatty acids, and short-chain fatty acids. DESIGN: Two groups of 12 healthy men with or without lactose malabsorption were selected with use of a breath-hydrogen test after a 30-g lactose load. Subjects were randomly assigned in a crossover design to 500 g/d of either fresh or heated yogurt for 2 periods of 15 d each, separated by a 15-d washout interval. RESULTS: Chronic consumption of fresh or heated yogurt had no detrimental effects on plasma glucose, insulin, or fatty acid areas under the curve in response to acute ingestion of 500 g yogurt in healthy men with or without lactose malabsorption. There were also no detectable changes in fasting plasma glucose, insulin, fatty acid, triacylglycerol, or cholesterol concentrations. In contrast, plasma butyrate was higher (P: < 0.03) and plasma propionate tended to be higher (P: = 0.059) in subjects without lactose malabsorption after fresh yogurt consumption than after heated yogurt consumption. There were no significant changes in plasma acetate. In subjects with lactose malabsorption, 15 d of fresh yogurt consumption also increased propionate production compared with values at baseline (P: < 0.04). In the same group, the production of breath hydrogen was lower after fresh yogurt consumption than after heated yogurt consumption (P: < 0.01). CONCLUSIONS: In men with lactose malabsorption, chronic consumption of yogurt containing live bacterial cultures ameliorated the malabsorption, as evidenced by lower breath-hydrogen excretion, but increased propionate concentrations. In subjects without lactose malabsorption, such yogurt tended to increase propionate and increased butyrate.

Adult↗
PubMed1983

The effects of lactose on the absorption and retention of dietary lead.

Intubated lactose has been shown to facilitate the absorption and retention of radiolabeled tracer lead in weanling rats. The conditions under which this effect may be observed are specified here. In acute radiotracer studies with fasted rats, absorption of intubated lead from the intestines and lead uptake into kidney, liver, blood and brain were increased by lactose (3-6 mg/g, per os) in rats 22 and 26 days of age postpartum. However, neither absorption nor uptake by kidney and liver were affected in the suckling rat (less than 21 days postpartum), nor beyond the first week after weaning. The facilitation by lactose of lead absorption and uptake was inhibited by carrier lead concentrations of 100 and 1000 ppm. Lactose at 80 mM (the concentration in rat's milk) had no effect on absorption and uptake of lead, nor on excretion of parenterally administered lead. Chronic feeding of 80 mM lactose and lead (0, 10, or 100 ppm in diet) reduced the retention of lead in kidneys and bones of weanling rats, fed both a normal (0.47%) and a calcium-deficient (0.02%) diet. It is concluded that intubations of high concentrations of lactose into fasted weanling rats can cause an increase in the absorption and uptake of lead. When fed to weanling rats at physiological concentrations, however, lactose actually reduces the retention of lead in bone and kidney.

Age Factors↗
PubMed1988

Dietary lactose improves endochondral growth and bone development and mineralization in rats fed a vitamin D-deficient diet.

Lactose promotes the intestinal absorption of calcium independent of the vitamin D endocrine system. The purpose of this study was to determine the effect of lactose supplementation on endochondral bone growth, bone development and mineralization in weanling rats fed a vitamin D-deficient diet. Rat pups were weaned from vitamin D-deficient dams and fed a vitamin D-deficient diet containing sucrose as the primary carbohydrate source or a similar diet but containing 20% lactose. After 4 wk, body weights, serum calcium levels and endochondral bone elongation rates in the lactose-fed animals were higher than in rats fed the sucrose diet. In addition, bone weights, bone calcium content, percent bone ash of bone dry weight, percent metaphyseal osseous tissues and bone osteoid content in the lactose-fed rats were different from those in the rats fed the sucrose diet. In all cases the changes in osseous tissues that were observed in the animals fed the lactose-supplemented diet were toward normal values as observed in age-matched animals fed a vitamin D-replete diet. The improvements in bone growth and development due to lactose supplementation occurred independent of the vitamin D endocrine system and are likely the result of improved calcium absorption in the intestine.

Animals↗
PubMed1997

Prevalence of lactose malabsorption in Galicia.

BACKGROUND: The aim of the current study was to evaluate the prevalence of lactose malabsorption (LM) in Galicia (NW Spain) in order to design nutritional intervention and/or public education strategies for high risk groups. METHODS: We conducted a study of LM by breath-hydrogen carbohydrate absorption test (BH2 test) in 850 healthy subjects. All subjects underwent BH2 tests following ingestion of a aqueous solution of 2 g lactose/kg body weight up to a maximum of 50 g. Subjects with LM were retested after ingesting 250 ml of milk and/or 250 ml of yogurt. RESULTS: The frequency of LM in the subjects who ingested 2 g lactose/kg body weight was 32.5%. This percentage decreased significantly with a decrease in the quantity of administered lactose and the vehicle was milk or yogurt-only 13.7% was LM after 250 ml of milk and 3.8% after 250 ml of yogurt. Gastrointestinal symptoms also depend on dosage of lactose and vehicle, decreasing from 54.3% after 2 g lactose/kg to 18.5% after milk and to 0% after yogurt. The frequency and number of gastrointestinal symptoms were significantly higher (p < 0.001) in LM than in lactose absorption (LA). CONCLUSIONS: Lactose malabsorption is prevalent in the population of Galicia. An important number of subjects identified as LM with usual clinical testing become LA when the ingestion of dairy products is limited so that the amount of lactose consumed is similar to that contained in a usual serving. Our results suggest the importance of BH2 testing following ingestion of usual consumed amounts of lactose per serving.

Adolescent↗
PubMed2002

Is lactose intolerance implicated in the development of post-infectious irritable bowel syndrome or functional diarrhoea in previously asymptomatic people?

OBJECTIVE: The relationship between lactose intolerance and post-infectious irritable bowel syndrome (IBS) in adults is uncertain. Bowel symptoms may persist after bacterial gastroenteritis and as post-infectious IBS. Acquired lactose intolerance may follow viral enteric infections in children. We compared the frequency of lactose intolerance after bacterial gastroenteritis in adults with and without symptoms of IBS or functional diarrhoea at 3-6-months' follow-up. DESIGN: A prospective cohort study was conducted. METHODS: All subjects with bacterial gastroenteritis confirmed by stool culture from the microbiology laboratory and without prior IBS or functional diarrhoea were eligible to participate. IBS and functional diarrhoea were diagnosed via self-completed Rome II modular questionnaires. Lactose intolerance was determined from a rise in breath hydrogen and plasma glucose and symptoms. RESULTS: One hundred and twenty-eight subjects with bacterial gastroenteritis were followed prospectively, from which a smaller cohort of 42 subjects took part in this study. The cohort was comprised of 24/25 subjects who developed post-infectious IBS (n = 16) or functional diarrhoea (n = 8) (9 male, 15 female) and 18 random controls (8 male, 10 female) chosen from the group without IBS or functional diarrhoea. The mean age of the subjects was 44.4 years (range 25-76 years). In the group with functional diarrhoea or IBS, four subjects had failure of the plasma glucose to rise but none had abnormal glucose hydrogen breath tests. In the control subjects, one had a positive combined test and six had failure of plasma glucose to rise alone. No subject developed symptoms during the test. CONCLUSIONS: Bacterial gastroenteritis did not cause persistent lactose intolerance in our study population. Lactose intolerance does not appear to be implicated in the aetiology of post-infectious bowel symptoms, including IBS. Advice to avoid dairy products in patients presenting with post-infectious IBS on the basis that they may have lactose intolerance appears unnecessary in patients from northern England.

Adult↗
PubMed1978

Maintenance of lactose secretion during acute insulin deficiency in lactating goats.

Induction of alloxan diabetes in 5 lactating goats resulted in reduced milk yields in 3 of the animals, while the yield was unchanged in two. After treatment of the diabetic goats with insulin for 4--5 days--the last 24 h intravenously--lactose secretion returned to the control values before alloxan administration provided that normoglycemia developed. In 2 experiments infusion of a large dose of insulin caused hypoglycemia and a 20--30 per cent reduction in lactose secretion rates. In the course of 1 h after withdrawal of the insulin infusion, patent signs of insulin deficiency developed as evidenced by steadily increasing plasma glucose concentrations. Nevertheless, lactose secretion continued at the same rate as during insulin infusion for the 4 h studied after discontinuation of the insulin infusion. In the goats where lactose secretion was reduced due to insulin-induced hypoglycemia, lactose secretion returned to control values when following discontinuation of insulin infusion the plasma glucose concentrations increased into normal and diabetic ranges. It is concluded that during insulin deficiency of short term duration, mammary lactose secretion was maintained at a normal rate. Since lactose is the major product of mammary glucose utilization, it is suggested that glucose uptake in the mammary gland was not reduced by short term insulin deficiency.

Acetoacetates↗
PubMed1978

Involvement of phosphoenolpyruvate in the catabolism of caries-conducive disaccharides by Streptococcus mutans: lactose transport.

The mechanisms for transport and hydrolysis of lactose were investigated in five cariogenic strains (HS6, AHT, FA1, NCTC 10449, and SL1) representing the four serogenetic groups of Streptococcus mutans. The systems for transport and hydrolysis of lactose had the characteristics of a phosphoenolpyruvate (PEP)-dependent lactose (Lac) phosphotransferase (PT) system and phospho-beta-galactosidase (P-beta-gal), respectively, in all strains tested, except strain HS6. Decryptified cells required PEP and Mg(2+) for transport of the non-metabolizable model beta-galactosides o-nitrophenyl-beta-d-galactopyranoside (ONPG) and thiomethyl-beta-d-galactopyranoside (TMG). Substitution of 2-phosphoglycerate (2-PG) for PEP also stimulated the Lac PT system. Other potential high-energy phosphate donors (adenosine tri-, di-, and monophosphates and guanosine triphosphate) did not stimulate the Lac PT system. Sodium fluoride had no effect upon the PEP-dependent Lac PT system in decryptified cells with PEP as the energy source; however, when 2-PG was used as the energy source, F(-) inhibited ONPG phosphorylation. With intact cells which must generate PEP endogenously, the presence of F(-) in concentration >/= 10 mM completely inhibited the Lac PT system, presumably through inhibition of 2-PG hydrolyase (EC 4.2.1.11; enolase). Both intact and decryptified cells accumulated a phosphorylated derivative of TMG that behaved chromatographically as TMG-phosphate. After alkaline phosphatase treatment, the derivative had an R(f) identical to that of TMG. No beta-galactosidase (beta-gal) activity was detected with ONPG as the substrate; hydrolysis occurred only when ONPG-6-phosphate was supplied as the substrate. Strain HS6 apparently transported lactose by an active transport-type system in which the accumulated intracellular product was the free disaccharide based on the following criteria: (i) ONPG transport and hydrolysis in decryptified cells was not stimulated by PEP; (ii) ONPG hydrolysis occurred in the absence of PEP; and (iii) ONPG-6-phosphate was not hydrolyzed. These data indicate that, in all strains tested except strain HS6, lactose transport was mediated by a PEP-dependent Lac PT system, resulting in accumulation of lactose-phosphate that was hydrolyzed by an enzyme similar to the P-beta-gal of group N streptococci and Staphylococcus aureus; conversely, strain HS6 transported and hydrolyzed lactose by a PEP-independent transport system and beta-gal, respectively.

Biological Transport↗
PubMed1983

Comparison of lactose uptake in resting and energized Escherichia coli cells: high rates of respiration inactivate the lac carrier.

The transport of lactose by Escherichia coli cells was radically different in the absence and in the presence of an exogenous energy source: in the former case, the time course of lactose accumulation was monotonous; in the latter case, lactose accumulation reached a maximum and then decreased to a final steady-state level lower than that observed in the absence of an energy source. We show that this "overshoot" is the result of a decrease in the influx rate and of an increase in the rate constant of efflux as lactose accumulates. These phenomena were irreversible. The extent of the overshoot was dependent upon the experimental conditions: it was maximal at alkaline pH, for low external potassium concentrations, and for relatively high external lactose concentrations (around or above the KT of uptake). The addition of an energy source to resting E. coli cells resulted in an increase in both the electrochemical gradient of protons and in the rate of respiration. We demonstrate that the overshoot is the result of the latter and unrelated to the former. We observed an irreversible decrease in the membrane potential as lactose accumulated in the presence of an exogenous energy source. We discuss the whole of our data in terms of an irreversible inactivation of the lactose carrier as a result of a possible interaction with the respiratory chain.

Edetic Acid↗
PubMed1983

Characterization of lactose transport in Kluyveromyces lactis.

We have determined that lactose uptake in Kluyveromyces lactis is mediated by an inducible transport system. Induction, elicited by lactose or galactose, of the transporter required protein synthesis. Transport of lactose required an energy-generating system and occurred by an active process, since an intracellular lactose concentration 175 times greater than the extracellular concentration could be obtained. The Km for lactose transport was about 2.8 mM in uninduced and lactose- or galactose-induced cells. The lactose transporters in K. lactis and Escherichia coli appear to be different since they respond uniquely to inhibition by substrate analogs.

2,4-Dinitrophenol↗
PubMed1985

Lactose metabolism in Erwinia chrysanthemi.

Wild-type strains of the phytopathogenic enterobacterium Erwinia chrysanthemi are unable to use lactose as a carbon source for growth although they possess a beta-galactosidase activity. Lactose-fermenting derivatives from some wild types, however, can be obtained spontaneously at a frequency of about 5 X 10(-7). All Lac+ derivatives isolated had acquired a constitutive lactose transport system and most contained an inducible beta-galactosidase. The transport system, product of the lmrT gene, mediates uptake of lactose in the Lac+ derivatives and also appears to be able to mediate uptake of melibiose, raffinose, and galactose. Two genes encoding beta-galactosidase enzymes were detected in E. chrysanthemi strains. That mainly expressed in the wild-type strains was the lacZ product. The other, the lacB product, is very weakly expressed in these strains. These enzymes showed different affinities for the substrates o-nitrophenyl-beta-D-galactopyranoside and lactose and for the inhibitors isopropyl-beta-D-thiogalactopyranoside and galactose. The lmrT and lacZ genes of E. chrysanthemi, together with the lacI gene coding for the regulatory protein controlling lacZ expression, were cloned by using an RP4::miniMu vector. When these plasmids were transferred into Lac- Escherichia coli strains, their expression was similar to that in E. chrysanthemi. The cloning of the lmrT gene alone suggested that the lacZ or lacB gene is not linked to the lmrT gene on the E. chrysanthemi chromosome. One Lac+ E. chrysanthemi derivative showed a constitutive synthesis of the beta-galactosidase encoded by the lacB gene. This mutation was dominant toward the lacI lacZ cloned genes. Besides these mutations affecting the regulation of the lmrT or lacB gene, the isolation of structural mutants unable to grow on lactose was achieved by mutagenic treatment. These mutants showed no expression of the lactose transport system, the lmrT mutants, or the mainly expressed beta-galactosidase, lacZ mutants. The lacZ mutants retained a very low beta-galactosidase level, due to the lacB product, but this level was low enough to permit use of the lacZ mutants for the construction of gene fusions with the Escherichia coli lac genes.

Acetyltransferases↗
PubMed1997

Role of conserved residues in hydrophilic loop 8-9 of the lactose permease.

A peptide motif, GXXX(D/E)(R/K)XG(R/K)(R/K), has been conserved in a large group of evolutionarily related membrane proteins that transport small molecules across the membrane. Within the superfamily, this motif is located in two cytoplasmic loops that connect transmembrane segments 2 and 3 and transmembrane segments 8 and 9. In a previous study concerning the loop 2-3 motif of the lactose permease (A. E. Jessen-Marshall, N. J. Paul, and R. J. Brooker, J. Biol. Chem. 270:16251-16257, 1995), it was shown that the first-position glycine and the fifth-position aspartate are critical for transport activity since a variety of site-directed mutations greatly diminished the rate of transport. In the current study, a similar approach was used to investigate the functional significance of the conserved residues in the loop 8-9 motif. In the wild-type lactose permease, however, this motif has been evolutionarily modified so that the first-position glycine (an alpha-helix breaker) has been changed to proline (also a helix breaker); the fifth position has been changed to an asparagine; and one of the basic residues has been altered. In this investigation, we made a total of 28 single and 7 double mutants within the loop 8-9 motif to explore the functional importance of this loop. With regard to transport activity, amino acid substitutions within the loop 8-9 motif tend to be fairly well tolerated. Most substitutions produced permeases with normal or mildly defective transport activities. However, three substitutions at the first position (i.e., position 280) resulted in defective lactose transport. Kinetic analysis of position 280 mutants indicated that the defect decreased the Vmax for lactose uptake. Besides substitutions at position 280, a Gly-288-to-Thr mutant had the interesting property that the kinetic parameters for lactose uptake were normal yet the rates of lactose efflux and exchange were approximately 10-fold faster than wild-type rates. The results of this study suggest that loop 8-9 may facilitate conformational changes that translocate lactose.

Amino Acid Sequence↗
PubMed1997

Suppressor analysis of mutations in the loop 2-3 motif of lactose permease: evidence that glycine-64 is an important residue for conformational changes.

A superfamily of transport proteins, which includes the lactose permease of Escherichia coli, contains a highly conserved motif, G-X-X-X-D/E-R/K-X-G-R/K-R/K, in the loops that connect transmembrane segments 2 and 3 and transmembrane segments 8 and 9. Previous analysis of this motif in the lactose permease (A. E. Jessen-Marshall, N. J. Paul, and R. J. Brooker, J. Biol. Chem. 270:16251-16257, 1995) has shown that the conserved glycine residue found at the first position in the motif (i.e., Gly-64) is important for transport function. Every substitution at this site, with the exception of alanine, greatly diminished lactose transport activity. In this study, three mutants in which glycine-64 was changed to cysteine, serine, and valine were used as parental strains to isolate 64 independent suppressor mutations that restored transport function. Of these 64 isolates, 39 were first-site revertants to glycine or alanine, while 25 were second-site mutations that restored transport activity yet retained a cysteine, serine, or valine at position 64. The second-site mutations were found to be located at several sites within the lactose permease (Pro-28 --> Ser, Leu, or Thr; Phe-29 --> Ser; Ala-50 --> Thr, Cys-154 --> Gly; Cys-234 --> Phe; Gln-241 --> Leu; Phe-261 --> Val; Thr-266 --> Iso; Val-367 --> Glu; and Ala-369 --> Pro). A kinetic analysis was conducted which compared lactose uptake in the three parental strains and several suppressor strains. The apparent Km values of the Cys-64, Ser-64, and Val-64 parental strains were 0.8 mM, 0.7 mM, and 4.6 mM, respectively, which was similar to the apparent Km of the wild-type permease (1.4 mM). In contrast, the Vmax values of the Cys-64, Ser-64, and Val-64 strains were sharply reduced (3.9, 10.1, and 13.2 nmol of lactose/min x mg of protein, respectively) compared with the wild-type strain (676 nmol of lactose/min x mg of protein). The primary effect of the second-site suppressor mutations was to restore the maximal rate of lactose transport to levels that were similar to the wild-type strains. Taken together, these results support the notion that Gly-64 in the wild-type permease is at a site in the protein which is important in facilitating conformational changes that are necessary for lactose translocation across the membrane. According to our tertiary model, this site is at an interface between the two halves of the protein.

Amino Acid Sequence↗
PubMed2003

Phosphorylation of Streptococcus salivarius lactose permease (LacS) by HPr(His ~ P) and HPr(Ser-P)(His ~ P) and effects on growth.

The oral bacterium Streptococcus salivarius takes up lactose via a transporter called LacS that shares 95% identity with the LacS from Streptococcus thermophilus, a phylogenetically closely related organism. S. thermophilus releases galactose into the medium during growth on lactose. Expulsion of galactose is mediated via LacS and stimulated by phosphorylation of the transporter by HPr(His approximately P), a phosphocarrier of the phosphoenolpyruvate:sugar phosphotransferase transport system (PTS). Unlike S. thermophilus, S. salivarius grew on lactose without expelling galactose and took up galactose and lactose concomitantly when it is grown in a medium containing both sugars. Analysis of the C-terminal end of S. salivarius LacS revealed a IIA-like domain (IIA(LacS)) almost identical to the IIA domain of S. thermophilus LacS. Experiments performed with purified proteins showed that S. salivarius IIA(LacS) was reversibly phosphorylated on a histidine residue at position 552 not only by HPr(His approximately P) but also by HPr(Ser-P)(His approximately P), a doubly phosphorylated form of HPr present in large amounts in rapidly growing S. salivarius cells. Two other major S. salivarius PTS proteins, IIAB(L)(Man) and IIAB(H)(Man), were unable to phosphorylate IIA(LacS). The effect of LacS phosphorylation on growth was studied with strain G71, an S. salivarius enzyme I-negative mutant that cannot synthesize HPr(His approximately P) or HPr(Ser-P)(His approximately P). These results indicated that (i) the wild-type and mutant strains had identical generation times on lactose, (ii) neither strain expelled galactose during growth on lactose, (iii) both strains metabolized lactose and galactose concomitantly when grown in a medium containing both sugars, and (iv) the growth of the mutant was slightly reduced on galactose.

Autoradiography↗
PubMed1968

Galactosidase activity of lactose-positive Neisseria.

The chromogenic substrate o-nitrophenyl-beta-d-galactopyranoside (ONPG) was hydrolyzed by lactose-positive Neisseria. Eight strains of pharyngeal origin were examined. In culture reactions, seven strains resembled Neisseria meningitidis with the exception that they produced acid from 1% (w/v) lactose. An eighth strain (V8) differed in that it did not form acid from maltose or from 1% lactose. However, acid formation was observed in 10% lactose cultures of strain V8, suggesting that entry of lactose occurred by passive diffusion, rather than as a result of permease activity. The enzymes which hydrolyzed ONPG were produced constitutively by the cells of all eight strains. Thus, specific activity in these strains was not increased by prior exposure to lactose, or to two other possible inducers, isopropyl-beta-d-thiogalactoside or methyl-beta-d-thiogalactoside. Study of cell-free extracts of one strain showed that the enzyme was heat-labile, having a half-life of 10 min at 45 C. The enzyme was unstable at low protein concentrations, but it was protected completely or partially when albumin or manganous ions were added. The enzyme appeared to be a typical beta-galactosidase: alpha-galactosides (melibiose and p-nitrophenyl-alpha-d-galactopyranoside) were not hydrolyzed, activity against ONPG was not dependent upon inorganic phosphate, and galactose was released by cleavage of ONPG. ONPG hydrolysis provided a simple and rapid method for detecting lactose-positive Neisseria.

Culture Media↗
PubMed1978

Inhibition of mammary gland lactose secretion by colchicine and vincristine.

The possible role of microtubules in milk production was examined in mammary gland slices from lactating guinea pigs. Colchicine, 10(-5)-10(-4) M, depressed lactose secretion within 15 min, maintaining maximal inhibition over 2.5 h, accompanied by retention of lactose within the slices. In colchicine dose-response studies (2 h, 10(-8)-10(-5) M), secretion was depressed 22% by 10(-5) M, whereas tissue lactose increased with dose up to +25% at 10(-5) M. Lactose synthesis was inhibited 3-19% without correlation to colchicine concentration. In another study, incubation with 10(-5) M lumicolchicine yielded one-third less inhibition of secretion than 10(-5) M colchicine with no increase in tissue lactose. Both drugs depressed synthesis 31%. Lactose secretion showed a negative correlation with 10(-7)-10(-4) M vincristine yielding a maximal 66% inhibition at 10(-4) M, whereas tissue retention showed a linear increase with concentration up to 151% of control at 10(-4) M. Effects on synthesis were sporadic. These data suggest that microtubules have a role in facilitating the transport and/or secretion of lactose and perhaps other milk components.

Animals↗
PubMed1991

Absorption of lactose from colon of newborn piglet.

Piglets in three age groups (1-3, 9-11, and 16-25 days after birth) were used for in vivo colonic perfusions. Studies compared an isosmolar (312 mosM) with a high osmolar (551 mosM) solution and two equimolar substrates (with hexose concentrations of 73.1 mM), lactose and glucose-galactose. From the isosmolar perfusates, lactose absorption was 0.43 +/- 0.04 in the 18-20 day olds and 1.04 +/- 0.2 mumol.cm-1.min-1 in the 1-3 day olds; absorption from the glucose-galactose solution was negligible in all age groups (less than 0.05 +/- 0.05 mumol.cm-1.min-1). From the high osmolar perfusate, lactose absorption also exceeded that of glucose and galactose. In a third set of perfusion studies, the concentration of lactose was varied between 15 and 240 mM perfusate. Five-day-old animals absorbed 67% more lactose than 18-day-old animals; the right colon absorbed 57% more than the left. Lactose absorption, correlated with its concentration in the perfusate (r = 0.99), was nonsaturable at concentrations up to 240 mM, and was correlated with the uptake both of sodium (r2 = 0.59 for young and 0.64 for older neonates) and of chloride (r2 = 0.55 for young and 0.31 for older neonates). The results suggest that lactose may be removed from the colon without apparent cleavage by beta-galactosidase.

Animals↗
PubMed2005

Preparation of dry powder inhalation with lactose carrier particles surface-coated using a Wurster fluidized bed.

An attempt was made to produce carrier particles for dry powder inhalation with lactose carrier particles surface-coated using a Wurster fluidized bed. The lactose carrier particles were coated with lactose aqueous solution containing hydroxypropyl methyl cellulose (HPMC) as a binder using a Wurster coating apparatus. Drug/carrier powder mixtures were prepared consisting of micronized salbutamol sulfate and lactose carriers under various particle surface conditions. These powder mixtures were aerosolized by a Jethaler((R)), and the in vitro deposition properties of salbutamol sulfate were evaluated by a twin impinger. The in vitro inhalation properties of the powder mixture prepared using the coated lactose carrier differed significantly compared with those of the powder mixture prepared using the uncoated lactose carrier, indicating improvements in in vitro inhalation properties of sulbutamol sulfate. In vitro inhalation properties increased with the surface coating time. This surface coating system would thus be valuable for increasing the in vitro inhalation properties of dry powder inhalation with lactose carrier particles.

Administration, Inhalation↗