Intestinal Lactase Activity Research Articles

MOLECULAR STUDY OF ADULT HYPOLACTASIA IN RABBIT AND HUMAN SMALL INTESTINE

In mammals, including most human populations, intestinal lactase activity is very high in the suckling and declines to low levels after weaning. There are two lactase phenotypes among human adults, one with persistent high lactase activity and one with hypolactasia(1). In the present study lactase mRNA levels have been measured by cDNA probes on northern blot of poly(A)+RNA normalized by B-actin in the small intestine of raboit, at different ages, and on slot blots of total RNA and polyiA)+RNA of human adults with persistent high lactase activity and with hypolactasia. An ECO RI-Hind III fragment covering more than the 5'-half of the rabbit lactase cDNA and the full human lactase cDNA were used as probes (2). mRNA levels have been compared with those of lactase activity (3). In the rabbit mRNA appears by the end of the gestational period and a level, comparable to that found in the suckling animal, is still present in the adult life. The lactase activity appears at the same time of the mRNA, but it declines to very low levels postweaning. Similarly, in man, at RNA level, no clear differences were found between adults with hypolactasia and adults with persistent high lactase activity. Conclusion: In adult mammals and in adult human hypolactasia, the control of lactase gene expression is very likely to be at a post-transcriptional level. 1) Auricchio S. et al. Lancet 2,324-326, 1963; 2) Mantei N. et al. The EMBO J.7, 2705-2713, 1988; 3) Asp NG. et al. Anal. Biochem. 47,527-538,1972.

Intestinal Infection with Nematospiroides Dubius Selectively Increases Lactase Expression by Mouse Jejunal Enterocytes

1. Intestinal structure, lactase (beta-galactosidase; EC 3.2.1.23) activity and alkaline phosphatase activity have been determined in mouse jejunal and ileal tissues before and during infection with the intestinal parasite Nematospiroides dubius. 2. Oral infection with small numbers of N. dubius larvae caused villus height, crypt depth and enterocyte migration rate to increase in the mouse jejunum. None of these effects occurred in ileal tissue. 3. Lactase activity also increased in jejunal, but not ileal, tissue of infected mice. This increase was associated with a doubling of the rate at which activity appeared in the brush-border membrane of enterocytes during migration over the basal regions of jejunal villi. Alkaline phosphatase activity in jejunal tissue remained unchanged in infected mice. 4. Attention is drawn to the fact that this is the first occasion when crypt cell hyperplasia has been found to be positively correlated with an increase in lactase activity and a decrease in cytotoxic/suppressor T-cells. Further work is needed to establish the primary cause of these effects.

Ability of Juvenile White Sturgeon (Acipenser transmontanus) to Utilize Different Carbohydrate Sources

Juvenile white sturgeon were fed isonitrogenous diets containing 27.2% glucose, fructose, maltose, sucrose, lactose, dextrin, raw corn starch or cellulose for 8 wk. Growth, body composition, plasma chemistry (with the exception of glucose), and liver glucose-6-phosphate dehydrogenase (G6PDH, EC 1.1.1.49), malic enzyme (EC 1.1.1.40) and isocitrate dehydrogenase (ICDH, 1.1.1.42) activities of sturgeon were significantly (P less than 0.05) affected by the different dietary carbohydrate sources. Sturgeon fed either the maltose or glucose diets had the highest percent energy retained, followed by those fed either the dextrin, raw corn starch or sucrose diets, whereas those fed either the lactose, fructose or cellulose diets had the lowest. Sturgeon fed either the maltose or glucose diets were hyperlipidemic, having twice the amount of plasma total lipid, triacylglycerol and total cholesterol as fish fed the other carbohydrate sources. These two carbohydrate sources were also more lipogenic: maltose- or glucose-fed sturgeon had significantly higher body lipid and liver G6PDH, malic enzyme, and ICDH activities. The poor ability of sturgeon to utilize either sucrose or lactose appears to be due to low intestinal sucrase (EC 3.2.1.48) and lactase (EC 3.2.1.108) activities. Intestinal aminopeptidase (EC 3.4.11.11), maltase (EC 3.2.1.20), sucrase and lactase activities of sturgeon were not affected by feeding different carbohydrate sources for 8 wk.

Intestinal lactase (beta-galactosidase) and other disaccharidase activities of suckling and adult common brushtail possums, Trichosurus vulpecula (Marsupialia:Phalangeridae)

Small-intestinal disaccharidase activities of eight suckling T. vulpecula, aged from 34 to 150 days, and of two adult animals were investigated. Intestinal maltase, isomaltase and sucrase activities increased with age, whereas lactase activities decreased. Trehalase activities were relatively high in all animals and showed no obvious age-related changes. Three separate beta-galactosidase activities, one neutral and two acid, acted on lactose. The neutral beta-galactosidase activity appeared to be due to a brush border enzyme similar to that of eutherian mammals, whereas the acid beta-galactosidases were soluble and probably of lysosomal origin. One of these, acid beta-galactosidase-1, had similar properties to the sole intestinal beta-galactosidase of macropodid marsupials, whereas the other, acid beta-galactosidase-2, has not previously been described. Galactosyl oligosaccharides isolated from macropodid milk were readily hydrolysed by both acid beta-galactosidases but not by the neutral beta-galactosidase. The total intestinal lactase activity in animals aged up to 125 days was due mainly to acid beta-galactosidase-1, whereas in older animals it was due mostly to the neutral beta-galactosidase; this suggests that late in lactation the young T. vulpecula change from a macropodid mode of digestion of galactosyl oligosaccharides to a eutherian mechanism for the digestion of lactose. These findings may have implications for the hand-rearing of orphaned T. vulpecula.

Low Intestinal Lactase Activity in Offspring from Ethanol-Treated Mothers

Some aspects of small intestine maturation have been studied in the newborns from chronic ethanol-treated pregnant rats (25% ethanol in drinking fluid) immediately after birth (before suckling) and after 30 days of life. Litters delivered by mothers fed ad libitum with a standard diet diluted 50% with cellulose were used as a nutritional control. At birth, pups from ethanol-treated mothers showed significant decreases in total intestinal length and thickness, low total lactase activity and low somatostatin intestinal content. The intestinal alterations of these neonatal parameters are not present in newborns from mothers on fiber-diluted diet. From delivery, pups from different experimental groups were nursed by normal lactating dams. At 30 days of age neither of those parameters differed among the groups. We propose that the low levels of total lactase activity in newborns from alcoholic mothers, that are a consequence of a lower intestinal mucosa content, are a direct effect of ethanol in utero on the fetal gastrointestinal system.

The effect of maturation and source of dietary protein on the capacity of the small intestine to hydrolize lactose in rats

The effect of maturation and quantity and different source of dietary protein on the evolution of intestinal lactase activity (LA) was studied in rats. The diets used were casein (12 and 20% protein) and rice and beans (12% protein) completed with vitamins, minerals, oil and starch (up to 100%) with or without lactose. In the first experiment, the offspring of rats fed these diets were studied at birth, at weaning and at 51 days of age. In the second experiment, the offspring were fed the same diets with or without lactose in different sequences. The parameters studied were small intestine LA and total LA in the intestinal homogenate. The data indicate that when lactose was present in the diet, the older rats exhibited low lactase specific activity but higher total LA than at birth.

Intestinal lactase and other disaccharidase activities of a suckling crabeater seal ( Lobodon carcinophagus)

1. 1. The intestinal disaccharidase activities of a suckling crabeater seal were investigated. 2. 2. Lactase, maltase, isomaltase and cellobiase activities were readily detected but trehalase and sucrase activities were absent. 3. 3. The intestinal homogenates were separated into a soluble (S2) fraction and a particulate brush border (P2) fraction. The lactase activities of the two fractions had different properties corresponding to those of an acid and a neutral β-galactosidase respectively. Approximately two-thirds of the total lactase activity measured at pH 6.0 was due to the acid β-galactosidase. 4. 4. The isomaltase and cellobiase activities were found almost exclusively in the particulate fractions but about one third of the maltase activity was in the S2 fraction. This soluble maltase activity appeared to be due to an acid maltase.

Cellular origin of lactase decline in postweaned rats

Intestinal lactase activity falls at weaning reaching low levels in the adult rat. Present work measures cellular migration rates and lactase activity along villi of intestines taken from rats of different ages to determine the cellular basis for this developmentally regulated fall in enzyme expression. An early fall in lactase activity taking place 15 to 23 days after birth was found to be associated with a shortening of the time available for lactase expression in brush-border membranes. A later fall in lactase activity occurring 23 to 46 days after birth was caused by an additional reduction in the rate at which lactase activity appeared in the brush-border membrane. These results are discussed in relation to previous work describing lactase biosynthesis in post-weaned rats.

Dependency of lactose absorption on lactase activity in starved rats.

The effects of starvation on intestinal disaccharidase activities and disaccharide absorption were studied in rats. Adult male rats were starved for either 16 or 72 h and the specific activity of lactase and sucrase was determined together with the absorption of lactose, sucrose, and glucose in vitro by the everted sac technique. The specific activity of lactase was significantly higher and the specific activity of sucrase was lower in the 72-h starved animals when compared with the 16-h starved group. The higher specific lactase activity in the 72-h starved animals was reflected in enhanced absorption of lactose as determined by the transfer of the constituent monosaccharides into the serosal fluid. The transfer of glucose into the serosal fluid by the glucose sac was also higher in the 72-h starved rats but not to the same extent as that of lactose. The absorption of sucrose was not significantly different between the two groups of animals. This study shows that the increase of intestinal lactase activity induced by starvation of adult rats correlates with in vitro increased lactose absorption.

Postnatal development of disaccharidase activities in jejunal fluid of preterm neonates.

Because human fetuses of 26-30 weeks gestation are known to have low levels of intestinal mucosal lactase activity, it has been assumed that live born preterm neonates of comparable gestational age are also lactase deficient. We have previously shown that disaccharidase activities in jejunal fluid in infants are highly significantly correlated with enzyme activities in the adjacent mucosa. We have now measured disaccharidase activities cross-sectionally and longitudinally in the jejunal fluid of a group of very preterm neonates of 26-29 weeks gestation who were fed with pasteurised human milk. Lactase activity was within the normal range for older infants and children within the first week of life. Sucrase: lactase ratios fell significantly in the second and third weeks of life, strongly suggesting a further increase in lactase activity. This increase was independent of postconceptional age. Preterm neonates are not as lactase deficient as previously believed, and this has implications in the search for optimal feeding regimes.

Neonatal intestinal lactase activity.

The sequential changes in intestinal lactase activity of 40 neonates were measured indirectly from the differential uptake and excretion of lactose and the non-metabolisable disaccharide lactulose contained in formula feeds. A daily decline in urinary lactose:lactulose excretion ratios, reflecting a rise in intestinal lactase activity, followed formula feeding. Percentage decline was related directly to gestation: full term infants displayed a fivefold greater decline in lactosuria than infants with a gestation of 28 weeks during the first 10 days of milk feeding. The difference between lactose:lactulose ingestion and excretion ratios suggests that within five days of starting feeds intestinal hydrolysis of lactose exceeds 98% efficiency, even in very preterm infants.

Effect of 1,25-dihydroxyvitamin D3 on intestinal disaccharidases in uremic rats.

The effect of 1,25-dihydroxyvitamin D3 (1,25-D) on the activity of intestinal disaccharidases, maltase, sucrase, trehalase and lactase, was studied in five-sixths nephrectomized uremic rats. In uremic rats, maltase, sucrase and trehalase activities were lower than in sham-operated rats. Administration of 1,25-D produced significant improvement of maltase, sucrase, trehalase and lactase activities in uremic rats. These results suggest that activities of intestinal disaccharidases are reduced in uremic rats and these activities are normalized after 1,25-D administration.

Lactase Insufficiency Revisited

The definition of "insufficient" small bowel lactase activity varies greatly among authors. The present study is aimed at redefining lactase insufficiency by comparing intestinal lactase activity and results of the lactose breath hydrogen test. Primary "insufficient" lactase activity was considered to be present when a child with a normal small bowel histology showed lactose malabsorption as measured by the lactose breath hydrogen test. The lactase activity of 22 "normal" children ranged from 0.77 to 4.57 U/g wet weight, while five children showed primary lactase insufficiency as defined above. Small bowel lactase activity in the latter patients was less than 0.74 U/g wet weight. Sucrase and maltase activities were similar in both groups of patients. We conclude that children with a normal small bowel histology should be considered to have primary lactase insufficiency when small bowel lactase activity is below 0.75 U/g wet weight.

Intestinal Lactase Synthesis during Postnatal Development in the Rat

To elucidate the mechanism of the developmental decline in intestinal lactase activity at weaning, we examined lactase synthesis in suckling and adult rats. Lactase was purified to homogeneity from pooled intestines of newborn rats and used to raise a monospecific antibody. Using this antibody, we developed a quantitative immunoprecipitation assay for lactase. Intestinal microvillus membrane proteins were labeled in 15-day and adult rats by intraluminal pulse-chase with 3H-leucine, and newly synthesized lactase quantified by immunoprecipitation. When lactase synthesis was expressed as the quantity of microvillus membrane lactase synthesized relative to total microvillus membrane protein synthesized, a significantly greater proportion of 3H-leucine incorporation into lactase was demonstrated in the suckling animals. No structural differences between newly synthesized suckling and adult lactase were observed when they were compared by SDS-polyacrylamide gel electrophoresis and fluorography. These data suggest that a change in the rate of lactase synthesis plays a role in the postweaning decline in enzyme activity.

The nature of maturational decline of intestinal lactase activity

We have examined the nature of the decline of lactase (EC 3.2.1.23) activity in the maturing rat intestine. It was established in an initial study that the activity decline reflected a proportional reduction in the concentration of the enzyme protein. Accumulation patterns into lactase, total intestinal proteins and sucrase (Ec 3.2.1.48)-isomaltase (EC 3.2.1.10) were compared, 4 h following administration of a tracer dose of [ 3H]leucine to weanling rats exhibiting a wide range of lactase decline. Accumulation of increasing amounts of label in total intestinal proteins and sucrase-isomaltase pools was found to accompany the lactase decline, in contrast to accumulation of a constant amount of label in the declining lactase pools. The pattern of increased label accumulation in total intestinal proteins was shown in a corollary study to reflect a corresponding acceleration of total protein synthesis. On this basis, the finding of a constant amount of label in the declining lactase pools suggested a constant synthesis of lactase. We proposed earlier that associated reductions in enterocyte life-span (leading to correspondingly less lactase accumulation) rather than suppressed synthesis may provide the primary causal basis of lactase decline in the postweaned mammal.

The influence of moderate lactose intake on intestinal lactase activity, protein utilization and energy digestibility in rats

ZusammenfassungDer Einfluß niedriger Laktosegaben auf die intestinale Laktaseaktivität, Proteinverwertung und Energieverdaulichkeit bei RattenDer Einfluß niedriger Laktosegaben auf die intestinale Laktaseaktivität, die Durchgangszeit, die Proteinausnutzung und die Verdaulichkeit der Energie wurde in Bilanzversuchen mit Ratten gemessen. Magermilchpulver und Kasein wurden als Proteinquellen benutzt. In dem auf Kasein basierenden Futter machte Laktose 0, 5, 10 bzw. 15% der Trockensubstanz aus. Alle Rationen wurden, teils ohne teils mit Zugabe von 0,7% Nebacitin, gegeben, um den Einfluß der intestinalen mikrobiellen Aktivität auf die erzielten Ergebnisse festzustellen. Die Laktaseaktivität wurde in dem Mukosagewebe des Dünndarms gemessen.Weder die wahre Verdaulichkeit noch die biologische Wertigkeit des Proteins wurden durch die Laktose im Futter beeinflußt. Dies deutet darauf hin, daß die Laktose schon im vorderen Teil des Magen‐Darmkanals völlig hydrolysiert und absorbiert wird. Die Laktaseaktivität im Dünndarm reichte dazu aus, die Laktosemengen, die in diesem Versuch mit dem Futter verabreicht wurden, zu hydrolysieren. Die Ergebnisse der Versuche der mit Nebacitinbehandelten Ratten unterstützen diese Hypothese insofern, als die Ausscheidung des Stickstoffs nicht von den Laktosegaben beeinflußt wurde, und unabhängig von der bakteriellen Aktivität im Darminhalt war. Die Eliminierung der ATP‐Aktivität im Blinddarminhalt durch Beigabe von Nebacitin war nahezu vollständig. Weder bei den Nebacitin‐behandelten noch bei den unbehandelten Ratten wurde die Verdaulichkeit der Energie durch Laktose beeinflußt. Ebenso wurde die Durchgangszeit nicht durch Laktose beeinflußt, obwohl Ratten mit reduzierter mikrobieller Aktivität eine signifikant verlängerte Durchgangszeit im Vergleich zu unbehandelten Ratten zeigten. Eine Auftrennung der totalen Stickstoffmenge im Kot zeigte, daß die verschiedenen Fraktionen nicht durch die Laktosegaben im Futter beeinflußt wurden. Ferner konnte gezeigt werden, daß die Stickstoffmengen, die von Bakterien und endogenem Zellabbau herrühren, im Kot von Ratten, die mit Nebacitin behandelt worden waren, drastisch reduziert wurden.

Intestinal lactase activity and calcium absorption in the aging female with osteoporosis.

In 11 postmenopausal women with histologically proven osteoporosis and normal lactose tolerance, a direct correlation between calcium absorption and intestinal lactase activity was observed. The results suggest that varying degrees of relative deficiencies in intestinal lactase might contribute to the graded decrease in calcium absorption which characterizes the aging female population.

Relation between dietary-induced increase of intestinal lactase activity and lactose digestion and absorption in adult rats.

To study the relation between dietary-induced increase of intestinal lactase activity and lactose absorption, 11-wk-old rats were fed either a high-starch (70 cal%), low-fat (7 cal%) diet or a low-starch (5 cal%), high-fat (73 cal%) diet for 7 days. Food intake and body weight changes were similar in the two dietary groups. In the first experiment, lactose absorption was studied in vivo after oral administration of 600 mg lactose (10% solution in water with added [3H]PEG) to rats fasted for 16 h. Groups of rats were killed at time 0 and at 1-h intervals for the next 3 h. Lactase activity and lactose absorption were significantly higher (P less than 0.01) in the high-starch group than in the low-starch group. In the subsequent experiment, 9-wk-old rats were fed the two isocaloric diets for 3 days. By use of the everted sac technique, we have demonstrated a significantly higher absorption of monosaccharides from lactose in the high-starch diet group; also, glucose transport was higher in the high-starch diet-fed animals. When Tris, an inhibitor of lactase, was added into the mucosal fluid, absorption of lactose was abolished and no effect was seen on glucose absorption (in vivo and in vitro). In both experiments, significant linear regression was established between lactase activity and lactose absorption. Our results thus show that the increase in lactase activity, induced by feeding a high-starch diet to adult rats, is accompanied by an increased capacity to hydrolyze lactose and absorb the constituent monosaccharides.

Persistence of high intestinal lactase activity in Pakistan.

In order to determine the incidence of persistence of high intestinal lactase activity (PLA) in a Pakistani human population, 53 probands belonging to the Punjabi ethnic group were examined using a lactose tolerance test. The incidence of PLA in the sample was found to be 55%, which has been compared with the incidence in other ethnic groups racially or geographically related to the Pakistani population. Various possible explanations for the fairly high incidence of PLA in the Punjabi ethnic group have been discussed.

Lactase activity is under hormonal control in the intestine of adult rat.

In the adult rat, starvation during 48 hours led to a three fold increase of lactase specific activity in the intestinal brush border membranes. Thyroxine injection during the three days before death (0.5 micrograms/g daily) inhibited the stimulation of lactase activity induced by starvation without modifying sucrase activity whereas hydrocortisone injections (25 micrograms/g daily) or thyroidectomy did not modify the stimulatory effect of starvation on lactase activity. These results suggests a specific hormonal control of intestinal lactase activity in the rat.