Biomedical subjects

S J Henning

Publications and source records attributed to S J Henning.

At least 37 records · Page 2Linked to original sources

PubMed1993

Inflammatory enzyme composition of the neonatal rat intestine: implications for susceptibility to ischemia.

Recent evidence has suggested that the immaturity of the neonatal intestine may play a key role in the development of ischemic injury. However, relatively little data exist on the susceptibility of the neonatal intestine to ischemic injury at various ages especially in the fed versus fasted states. In this study, the levels of xanthine oxidase ([XO] an enzyme which is a known, major source of free radicals in postischemic tissue) and myeloperoxidase ([MPO] an index of tissue neutrophil infiltration) were measured in 1-, 5-, 10-, 15-, and 20-day-old Sprague-Dawley rats. Rats were divided into fed (n = 8/day) and fasted (n = 8/day) groups 4 hours prior to sacrifice. The entire small intestine was removed and divided into five segments: the duodenum, proximal jejunum, distal jejunum, proximal ileum, and distal ileum. The specimens were homogenized and assayed for XO and MPO levels. A significant increase in XO was observed in the fasted animals compared to the fed animals on all days. Peak levels in XO were observed in both groups from day 5 to 10. MPO levels were significantly higher in the fasted versus fed animals on day 1. MPO levels decreased as the animals aged. These data demonstrate dramatic differences in the levels of inflammatory enzymes of the newborn rat in the fed versus fasted states. Also, marked variations with age are seen in both XO and MPO. Whether the XO and MPO levels present at the time of ischemic insult affect severity of injury remains to be seen.

Animals↗

PubMed1993

Hormonal regulation of the mRNA for cysteine-rich intestinal protein in rat jejunum during maturation.

Cysteine-rich intestinal protein (CRIP) has been implicated as an important zinc-binding protein in the rat intestine. However, its specific role remains undefined. As an approach to the ultimate elucidation of the function of CRIP, we have explored the role of glucocorticoids and L-thyroxine (T4) in the increase of CRIP mRNA that occurs during postnatal development. Hydrocortisone administration on day 10 elicited a precocious increase of CRIP mRNA. The response to hydrocortisone was readily detectable 12 h after injection. Lack of endogenous glucocorticoids in rat pups adrenalectomized on day 9 impeded but did not prevent the normal rise of CRIP mRNA. Furthermore, injections of dexamethasone (DEX) on days 10, 16, and 18 led to a loss of responsiveness of CRIP mRNA as the pups matured. The administration of T4 alone resulted in a small increase of CRIP mRNA, whereas when combined, T4 and DEX synergistically raised the concentration of CRIP mRNA. All of these patterns of response to hormone manipulation indicate the possibility that CRIP is a mediator of glucocorticoid action on the developing intestine. They do not appear to support the hypothesis that CRIP plays a role in zinc transport during the postnatal period. The potent effects of glucocorticoids and T4 on CRIP mRNA levels should provide useful tools for further investigations in this area.

Adrenalectomy↗

PubMed1993

Ontogeny of sucrase-isomaltase gene expression in rat intestine: responsiveness to glucocorticoids.

The goal of our study was to determine how sucrase-isomaltase (SI) gene expression in the rat small intestine is modulated by glucocorticoids during the second and third postnatal weeks. SI mRNA was quantitated by Northern blot and was compared with sucrase activities in the same tissue samples. The role of endogenous glucocorticoids was assessed by measuring SI mRNA and enzyme activity in rat pups adrenalectomized (ADX) on postnatal day 9. ADX pups showed a retarded appearance of sucrase activity compared with sham-operated control pups, and the appearance of SI mRNA paralleled the enzyme activity. To determine the role of exogenous glucocorticoids, a saturating dose of dexamethasone (Dex) was administered daily in three series of experiments starting on days 10, 16, and 18. In the day 10 series, Dex caused precocious appearance of both SI mRNA and sucrase activity. In the day 16 series, Dex accelerated the rate of rise of the two parameters, whereas by day 18 there was no significant effect of Dex. To investigate whether the accelerated rise in the day 16 series was associated with changes in epithelial cell kinetics, the location of SI protein was assessed by immunofluorescence staining. The results indicated that the effect of Dex at this age was due to faster emergence of SI-bearing enterocytes from the intestinal crypts.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1992

A gradient in expression of the Escherichia coli heat-stable enterotoxin receptor exists along the villus-to-crypt axis of rat small intestine.

Binding of Escherichia coli heat-stable enterotoxin to its receptor is critical to the initiation of toxin-induced secretion and diarrheal disease; it is also likely, however, that this receptor binds an endogenous ligand. In order to characterize the expression of the heat-stable enterotoxin receptor in the small intestine, we isolated epithelial cells from villus tip to crypt in rat jejunum and ileum. Binding of radiolabeled toxin was maximal in the villus preparations and gradually decreased along the villus-to-crypt axis, paralleling the decline of sucrase activity. Northern blots of total RNA identified a single heat stable enterotoxin receptor transcript (3.8 kb), predominantly in the villus cell fractions. In situ hybridization demonstrated clear signal in the villus cells with no apparent signal in the crypt cells, lamina propria or muscularis. Expression of this receptor was greatest after enterocytes leave the proliferative cycle and enter villi. This pattern of gene and protein expression may reflect a role of this receptor in binding endogenous ligands which in turn may regulate intestinal ion flux along the villus-to-crypt axis.

Animals↗

PubMed1992

Effect of oral insulin on lactase activity, mRNA, and posttranscriptional processing in the newborn pig.

Insulin, found in human and pig colostrum and mature milk, appears to influence small intestinal growth and development. Ileal lactase activity is increased when porcine insulin is added to feedings administered to newborn piglets. We studied 2-day-old miniature piglets to determine whether the increase in lactase activity is accompanied by changes in enterocyte expression of lactase activity, steady-state levels of lactase mRNA, and/or posttranscriptional changes in lactase processing. We randomized the piglets to receive bottle feedings of a swine-weaning milk formula with (group F + I) or without (group F) the addition of 85 mU/ml of regular porcine insulin. The piglets were fed for 6 days (to 8 days of age), after which they were killed and the small intestine removed for analysis. Despite large differences between groups in enterocyte expression of lactase activity in the ileum, no differences were noted in the level of ileal lactase mRNA. The relative proportions of the 207, 210, and 230 kDa precursors of the 160 kDa mature lactase protein were similar between groups. These data indicate that the insulin-induced increased expression of ileal lactase activity is not regulated at the level of its mRNA or at the level of processing of the polypeptide.

Administration, Oral↗

PubMed1992

Synergistic effects of thyroxine and dexamethasone on enzyme ontogeny in rat small intestine.

The synergistic effects of dexamethasone (DEX) and thyroxine (T4) on the postnatal maturation of the 13-d-old rodent small intestine has been studied. Previous studies have shown that hydrocortisone and T4 produced a synergistic response in enzyme maturation. However, T4 elevates corticosteroid-binding globulin, which reduces the clearance of hydrocortisone. Thus, the apparent synergy between T4 and hydrocortisone may have been due to increased glucocorticoid availability. DEX, which does not bind to corticosteroid-binding globulin, was given (d8-12) at 25 pmol (i.e. 0.01 micrograms)/g body wt/d as established by a dose-response study in which this dose of DEX induced one third the maximum response in sucrase activity. In this way, synergy with T4 (130 pmol/g body wt/d, i.e. 0.1 micrograms/g body wt/d, d 5-12) could still be observed. Glucoamylase, lactase, acid beta-galactosidase, alkaline phosphatase, and sucrase activities were determined in two regions of the small intestine. Overall, the results for the two hormones administered alone showed intestinal maturation to be not significantly affected in the T4 group and partially stimulated in the DEX group. When combined, DEX + T4 synergistically increased jejunal sucrase, ileal glucoamylase, and duodenal alkaline phosphatase, and lowered ileal acid beta-galactosidase. The striking exceptions to the general pattern were two brush border enzymes that normally decline during intestinal maturation, namely ileal alkaline phosphatase and jejunal and ileal lactase. For these enzymes, DEX alone did not elicit precocious maturation, and there was no evidence for a synergistic interaction of these two hormones. Serum corticosterone concentrations also were measured. When corticosterone concentrations were compared with enzyme activity, no correlation was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Alkaline Phosphatase↗

PubMed1992

Apolipoprotein B messenger RNA editing in rat liver: developmental and hormonal modulation is divergent from apolipoprotein A-IV gene expression despite increased hepatic lipogenesis.

Rat hepatic apolipoprotein B (apoB) mRNA editing is regulated developmentally as well as by hormonal and nutritional modulation of hepatic lipogenesis, changes previously associated with coordinate modulation of hepatic apoA-IV gene expression. We have examined the effects of dexamethasone administration on apoB mRNA editing and the expression of other apolipoprotein genes in both neonatal and adult rats. Administration of dexamethasone increased hepatic triglyceride content in neonatal rats and increased hepatic but not intestinal apoA-IV mRNA abundance. However, neither the developmental profile nor the extent of hepatic apoB mRNA editing was changed after hormone administration. Dexamethasone produced a dose-dependent increase in adult hepatic triglyceride content and a coordinate fourfold increase in hepatic but not intestinal apoA-IV mRNA abundance, and hepatic and serum apoA-IV protein concentrations. Immunocytochemical localization revealed apoA-IV to be expressed in hepatocytes around the central vein while dexamethasone treatment produced a dose-dependent appearance of fat-filled hepatocytes throughout the lobule that were immunoreactive for apoA-IV. Despite these changes in hepatic triglyceride accumulation there was no change in the extent of hepatic apoB mRNA editing at any dose of dexamethasone. The data suggest that hormonal and metabolic modulation of hepatic apoB mRNA editing may be independent of factors that modulate apoA-IV gene expression despite alterations in hepatic triglyceride content.

Animals↗

PubMed1992

Expression of sucrase-isomaltase mRNA along the villus-crypt axis in the rat small intestine.

Sucrase-isomaltase has been used as a marker enzyme to study cell differentiation along the intestinal villus-crypt axis. Previous studies are in agreement that sucrase activity is confined to villus epithelial cells. However, immunoreactivity data are at conflict, with some studies reporting sucrase antigen in crypts as well as villi. To resolve this discrepancy, our goal was to determine the distribution of sucrase-isomaltase mRNA. A cDNA clone representing 3.0 kb of rat sucrase-isomaltase, including the sucrase active site, was characterized. Northern analysis of 12 tissues demonstrated a 6 kb transcript only in the small intestine. Jejunal cell fractions prepared by a washing technique showed declining levels of both sucrase activity and sucrase-isomaltase mRNA as well as increasing levels of thymidine kinase activity from early to later fractions. Since later fractions did not yield pure crypt cells, in situ hybridization using an 35S-labeled sucrase-isomaltase riboprobe was performed. The transition from zero to intense signal at the crypt-villus junction leads us to conclude that in the adult rat, sucrase-isomaltase gene expression is initiated only after cells leave the proliferative cycle and migrate onto the villi.

Amino Acid Sequence↗

PubMed1990

Development and tissue distribution of sucrase-isomaltase mRNA in rats.

Previous studies of sucrase-isomaltase (SI) activities have shown this complex to be absent in the suckling rat and to appear during the weaning period. We describe here the cloning of a heterologous SI cDNA and its use for the quantitation of SI mRNA as a first step toward understanding the molecular basis of SI development. A survey of RNA from 12 tissues of mature rats by Northern blot analysis showed a 6-kb band of SI mRNA only in the small intestine. Within the latter, both sucrase activity and SI mRNA peaked in the jejunum. Assay of jejunal tissue from developing rats showed sucrase activity and SI mRNA to be first detectable at 18 days, to rise in parallel through 24 days, and then to diverge a little (enzyme activity being lower) by 36 days. When glucocorticoid was administered to 10-day-old rats, neither sucrase activity nor SI mRNA was detectable 12 h later. Both parameters were readily detected 24 h postinjection, although the mRNA had risen relatively more than the enzyme activity. The two parameters increased in concert through 5 days postinjection and then plateaued. We conclude that, with respect to distribution along the intestine and to normal and precocious development, activities of SI in the rat are determined primarily by the abundance of its mRNA.

Aging↗

PubMed1989

A noninvasive method for determining patterns of milk intake in the breast-fed infant.

A noninvasive adaptation of the test-weighing method has been devised for continuously monitoring milk intake in breast-fed infants. This procedure consists of counting the number of swallows from videotaped sessions of individual feeds and correlating them to the corresponding pre- and postnursing weights of the infants. The method has been tested on four nursing sessions in twins aged 1 1/2 to 2 1/2 months. A high correlation was found between swallow counts and weight gain of the babies. The patterns of milk intake as monitored by these two parameters were similar. This method has the advantage of not disrupting the natural nursing process because test-weighing during the feeding session is not necessary. In addition, it allows for longitudinal studies and uses relatively simple equipment, i.e., a balance and a video camera. It is further suggested that monitoring swallowing in the manner described herein may be a valuable addition to studies on sucking behavior in human infants. Finally, it is noted from the data presented that the pattern of milk transfer in a mother breast-feeding twins is different from that observed in mothers breast-feeding singletons who were monitored by means of a cross-sectional test-weighing procedure.

Breast Feeding↗

PubMed1989

Fate of milk calcium in the gastrointestinal tract of suckling rats.

In the rat, as in many other mammals, the majority of milk Ca is associated with casein micelles. Because luminal proteolysis is immature in the suckling rat, we investigated the hypothesis that milk Ca remains in the macromolecular form as it traverses the stomach and upper small intestine. When intestinal contents of rat pups were examined 1 h after gavage with 45Ca-milk, 98% of the 45Ca was found to be in a soluble form. Surprisingly, chromatography on Sephadex G-10 showed it to have a molecular weight in the range of that of Ca2+. Analysis of gastric contents showed the stomach to be the initial site of release of Ca from the casein micelles. Although only 45% of the 45Ca was in a soluble form in stomach contents, 100% of this soluble 45Ca behaved as Ca2+. Comparison with the fate of 32P from milk confirmed the suggestion that most of the Ca is released as Ca2+. In vitro studies suggested that this release is the result of simple dilution or the combined action of intrinsic milk enzymes and dilution. Because milk Ca appears to enter the small intestine as Ca2+, we presume its mechanism of absorption in suckling animals is the same as that already established using simple salts of Ca. Nevertheless, the slow release from the bound form may be important in establishing the physiological pattern of Ca absorption in the infant. Implications of this for the supplementation of milks for low-birth-weight human infants is discussed.

Animals↗

PubMed1989

Roles of plasma clearance and corticosteroid-binding globulin in the developmental increase in circulating corticosterone in infant rats.

The aim of this study was to determine the role of plasma clearance in the developmental increase in plasma corticosterone concentration in the infant rat. Previous studies indicated that the corticosterone rise may be mediated entirely by a decrease in the MCR. The rationale of the current study was that if this is true, then corticosterone from an exogenous source (at a constant dose) should also produce a developmental increase in circulating levels of the hormone. Therefore, infant rats, aged 12, 16, and 21 days (i.e. near the beginning, middle, and end of the endogenous corticosterone developmental rise), were adrenalectomized and provided with a constant dose of corticosterone via sc pellets. There was a significant age-related increase in plasma corticosterone in pellet-treated pups which closely paralleled that seen in sham-operated littermates. This indicates that the decrease in plasma clearance is sufficient to account entirely for the normal developmental rise in plasma corticosterone. The declining MCR for corticosterone with increasing age is due primarily to a decrease in the apparent volume of distribution (Vd), which, in turn, may result from the concurrent increase in plasma corticosteroid-binding globulin (CBG). To investigate this possibility, the Vd of dexamethasone, a synthetic glucocorticoid that does not bind to CBG, was determined and compared with that of corticosterone. While the Vd of corticosterone declined significantly with age, there was no consistent change in the Vd of dexamethasone. Taken together, these data indicate that the decrease in clearance of corticosterone from plasma with increasing age is sufficient to account for the normal developmental rise of corticosterone. Moreover, increased binding of corticosterone to CBG appears to be responsible for decreases in Vd and clearance.

Adrenalectomy↗

PubMed1989

Hormone-dependent beta-casein mRNA stabilization requires ongoing protein synthesis.

The role of ongoing protein synthesis in mediating the posttranscriptional effects of hormones on casein gene expression in the COMMA D mouse mammary epithelial cell line was investigated using the protein synthesis inhibitors, cycloheximide and anisomycin. When COMMA D cells were pretreated with insulin and PRL for 24 h, the addition of glucocorticoids induced a greater than 20-fold increase in beta-casein mRNA accumulation with an apparent lag of greater than 8 h. Addition of cycloheximide and anisomycin not only prevented this increase, but unexpectedly, resulted in the rapid disappearance of preexisting beta-casein mRNA with a half-life of approximately 2 h. Under the same conditions, the levels of beta-actin and histone H4 mRNAs were increased markedly. In contrast, when cells were pretreated with all three lactogenic hormones for 48 h before the addition of either protein synthesis inhibitors or actinomycin D, the effects of these inhibitors on the levels of beta-casein mRNA were greatly diminished. This differential sensitivity of beta-casein mRNA to protein synthesis inhibitors was observed only in cells pretreated for greater than 24 h with all three hormones. Experiments performed in the absence of inhibitors indicated that beta-casein mRNA has a long half-life even after hormone withdrawal. These results suggest that hormone-dependent stabilization of cytoplasmic beta-casein mRNA requires ongoing protein synthesis. Cells cultured in the presence of all three lactogenic hormones slowly accumulate a labile protein(s), which exerts a selective effect on casein mRNA stability.

Actins↗

PubMed1989

Relative contribution of promoter and intragenic sequences in the hormonal regulation of rat beta-casein transgenes.

In order to identify DNA sequences responsible for the regulation beta-casein gene expression, lines of transgenic mice bearing the entire rat beta-casein gene and two rat beta-casein promoter chloramphenicol acetyltransferase (CAT) fusion genes have been established. All three transgenes have been shown previously to be regulated in a tissue- and stage specific manner. To investigate the relative contribution of promoter and intragenic sequences in the hormonal regulation of the beta-casein gene, mammary explant cultures derived from these lines of mice have now been performed, and the effects of PRL and glucocorticoids on transgene as compared with endogenous beta-casein gene expression have been quantified. After the addition of PRL to cultures performed in the presence of insulin and glucocorticoids, a 25- to 40-fold induction of endogenous mouse beta-casein mRNA was observed after 48 hr. A comparable greater than 25-fold induction of transgene expression after PRL addition was observed in explant cultures derived from a line of mice expressing the entire rat beta-casein gene. In contrast, PRL addition elicited only a 1- to 4.5-fold increase in CAT activity in cultures derived from two lines of mice bearing casein-CAT fusion genes with either 524 or 2300 base pairs of 5'-flanking DNA. In the presence of insulin, glucocorticoid or PRL addition alone increased endogenous beta-casein gene expression 2- to 2.5-fold and 5- to 10-fold, respectively, but only a 1.2- to 2.5-fold induction of CAT activity was observed for each hormone.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

A new method for the artificial raising of infant rats: the palate cannula.

Chronic removal of infant rats from their mother prior to the onset of weaning is complicated by the fact that young rats do not easily suckle from an artificial nipple. Thus, a method of artificial raising is advantageous for developmental investigations of nutrition or ingestive behaviors during the suckling period. The intragastric cannula has become a popular method for this purpose. However, for many studies, it would be advantageous if the diet could be administered to the mouth and actually swallowed by the young rat. We developed a new cannulation procedure which accomplishes these goals. Infant rats were removed from their mother on postnatal day 13 and fitted with a cannula that opened into the oral cavity through the hard palate. Liquid diet was administered by an infusion pump through the cannula for the subsequent 5 days. Growth was assessed by daily measures of body and organ weight. The results indicate that from postnatal day 13 on, the palate cannula can allow the continuation of normal growth patterns and eliminates certain complicating factors associated with other forms of artificial raising.

Animals↗

PubMed1988

Absorption and transport of milk calcium by infant rats.

All previous studies of Ca absorption in the developing animal have used simple salts of Ca. The aims of the current study are 1) to determine the predominant form of Ca in rat milk and 2) to compare the absorption of milk Ca and CaCl2. In vivo-labeled rat milk was obtained by injecting lactating dams with 45CaCl2. Distribution of 45Ca in the cream, whey, and casein fractions was determined by differential centrifugation, the values being 0.3, 5, and 95%, respectively. To study Ca absorption, rats aged 14 and 28 days received either 45Ca-milk or 45CaCl2 by intragastric intubation. At 14 days, transport of milk Ca into the carcass was significantly slower than that of CaCl2, although by 6 h postintubation both had plateaued at approximately 92% of dose. At 28 days, the time course of transport was the same for the two forms of Ca, and the plateau was not significantly different from that at 14 days. In the younger animals, more Ca from milk than from CaCl2 was retained in gastrointestinal tissue. Quantitation of 45Ca in various segments of the gastrointestinal tract showed that the greater retention of milk Ca occurred in the stomach, the duodenum, and the distal jejunum. We conclude that milk Ca is efficiently absorbed by the suckling rat, possibly in a protein-bound form. The mechanism of the absorptive process awaits further investigation.

Absorption↗

PubMed1988

The distribution of lead in milk and the fate of milk lead in the gastrointestinal tract of suckling rats.

Milk can be a significant source of lead (Pb) for young mammals, including humans. Certain essential trace elements have previously been shown to be specifically associated with particular milk components and such associations often increase bioavailability. Thus, the first goal of this study was to determine the distribution of Pb in cream, casein, and whey fractions of various milks under various conditions using 203Pb as a tracer. In rat milk almost 90% of the Pb was found to be associated with the casein micelles, regardless of: 1) whether the milk was labeled in vivo or in vitro; b) whether the milk was fresh or frozen; and c) the added concentration of Pb (over the range 0.01-75 micrograms/ml). The remainder of the Pb was approximately equally distributed between cream and whey. A virtually identical pattern of Pb distribution was observed with bovine milk. Pb added to infant formula also associated predominantly with casein micelles, although the Pb content of this fraction was significantly less than with rat and bovine milks. The second goal of the study was to determine if Pb remained associated with casein as it traversed the gastrointestinal tract of infant rats. For this purpose, rat pups aged 15-16 days were gavaged with 203Pb-labeled rat milk, and lumenal contents from the stomach and small intestine were collected 2 h later. Differential centrifugation of the homogenized lumenal contents showed that in the stomach the Pb was associated primarily with the casein curd. By the time chyme reached the distal small intestine, Pb was found predominantly in a fraction that was not precipitable by high-speed centrifugation (thus, not intact casein micelles), but was nondialyzable. We conclude that Pb in milk is protein bound and remains this way as it traverses the stomach and proximal small intestine of the infant rat.

Animals↗

PubMed1988

The miniature pig as an animal model for the study of intestinal enzyme development.

Studies of intestinal enzyme development and regulation relevant to the human infant require an animal model with a rate of maturation similar to that of the human infant. Hanford miniature pigs were weaned at 3 days of age to a standard swine weaning formula. At 1, 2, 3, 4, 5, and 6 wk of age, duodenal jejunal, and ileal segments were analyzed for protein content and lactase, sucrase, maltase, glucoamylase, and acid beta-galactosidase activities. Protein content of the small intestine changed significantly with age only in the ileum (p less than 0.05). Lactase activity fell significantly with age in all segments of the small intestine (p less than 0.001); activity was highest in the jejunum. Sucrase and maltase activities were present in all segments of the small intestine at 1 wk of age. Sucrase increased significantly (2-fold, p less than 0.02) with age only in the ileum and maltase increased significantly with age in the jejunum (by 50%, p less than 0.05) and the ileum (3-fold, p less than 0.001). Activities were highest in the jejunum. Glucoamylase activity was present at 1 wk of age and showed a small but significant increase with age only in the duodenum (p less than 0.005). Acid beta-galactosidase activity demonstrated small but significant decreases with age in all small intestinal segments. Glucoamylase and acid beta-galactosidase activities were similar in all segments. In the 6-wk-old pigs, activities of all the enzymes tested were similar to those found in young human infants.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗