Evidence, not eminence, for surgical management during COVID-19: a multifaceted systematic review and a model for rapid clinical change.

BACKGROUND: Coronavirus (COVID-19) forced surgical evolution worldwide. The extent to which national evidence-based recommendations, produced by the current authors early in 2020, remain valid, is unclear. To inform global surgical management and a model for rapid clinical change, this study aimed to characterize surgical evolution following COVID-19 through a multifaceted systematic review. METHODS: Rapid reviews were conducted targeting intraoperative safety, personal protective equipment and triage, alongside a conventional systematic review identifying evidence-based guidance for surgical management. Targeted searches of PubMed and Embase from 31 December 2019 were repeated weekly until 7 August 2020, and systematic searches repeated monthly until 30 June 2020. Literature was stratified using Evans' hierarchy of evidence. Narrative data were analysed for consistency with earlier recommendations. The systematic review rated quality using the AGREE II and AMSTAR tools, was registered with PROSPERO, CRD42020205845. Meta-analysis was not conducted. RESULTS: From 174 targeted searches and six systematic searches, 1256 studies were identified for the rapid reviews and 21 for the conventional systematic review. Of studies within the rapid reviews, 903 (71.9 per cent) had lower-quality design, with 402 (32.0 per cent) being opinion-based. Quality of studies in the systematic review ranged from low to moderate. Consistency with recommendations made previously by the present authors was observed despite 1017 relevant subsequent publications. CONCLUSION: The evidence-based recommendations produced early in 2020 remained valid despite many subsequent publications. Weaker studies predominated and few guidelines were evidence-based. Extracted clinical solutions were globally implementable. An evidence-based model for rapid clinical change is provided that may benefit surgical management during this pandemic and future times of urgency.

A method for collecting breath samples from individual chickens for analysis of 13CO(2), H(2), and CH(4).

This study describes experiments using simple helmets to collect breath samples from individual birds for measurement of (13)CO(2), H(2), and CH(4), which form the basis for various diagnostic tests for intestinal dysfunction in humans. Peak enrichment in (13)C in breath CO(2) occurred between 5 and 30 min postingestion by 18-d-old chickens administered a gelatin capsule containing approximately 3.6 mg of (13)C-octanoic acid dissolved in vegetable oil. For 25-d-old chickens given 10 mL of homogenized cooked corn by oral gavage, peak enrichment occurred 60 to 90 min postingestion. In fully fed 25-d-old chickens, H(2) and CH(4) concentrations in breath ranged from 7 to 115 ppm and from 0 to 5.5 ppm, respectively. Following an overnight fast, H(2) and CH(4) concentrations in breath ranged from 0.5 to 7.5 ppm and 0 to 3.0 ppm, respectively, in the same chickens. Ranges in H(2) (1.0 to 56.5 ppm) and CH(4) (0 to 8.0 ppm) concentrations widened considerably 3 h after oral gavage with approximately 130 mg of lactulose (an indigestible disaccharide) dissolved in 5 mL of water. The results from these investigations indicate that collection of re-breathed air samples from chickens is plausible, which opens the way for development of noninvasive methods for evaluating gastrointestinal functions in chickens.

Bacterial modulation of small intestinal goblet cells and mucin composition during early posthatch development of poultry.

Mucins possess potential binding sites for both commensal and pathogenic organisms and may perform a defensive role during establishment of the intestinal barrier. To observe the effects of bacteria on intestinal goblet cell mucin production during posthatch development, differences in the small intestine of conventionally reared (CR) and low bacterial load (LBL) broiler chicks were examined. Jejunal and ileal goblet cells were stained with either periodic acid-Schiff stain or high iron diaminealcian blue pH 2.5 to discriminate among neutral, sulfated, and sialylated acidic mucins. Total goblet cell numbers and morphology of goblet cells containing neutral and acidic mucins did not differ significantly between CR and LBL birds. However, significant differences in acidic mucin composition from primarily sulfated to an increase in sialylated sugars at d 4 posthatch were observed in CR chicks, with greater numbers of jejunal and ileal goblet cells displaying this mucin type (CR, 0.5 +/- 0.1 x 10(3) cells/mm(2); LBL, 0.04 +/- 0.02 x10(3) cells/mm(2)). This change in mucin profile in response to bacterial colonization suggests a potential role as a protective mechanism against pathogenic invasion of the intestinal mucosa during early development.

Characterization of transport systems for cysteine, lysine, alanine, and leucine in wool follicles of sheep.

Aspects of the uptake of the AA Cys, Leu, Ala, and Lys into wool follicles were investigated using short-term culture of thin strips of sheep skin. Following verification of the reliability of the model system, the sites of uptake of the radiolabeled AA were shown to differ and to be consistent with their different roles in fiber production. Cysteine appeared in the zone of keratinization immediately distal to the follicle bulb. Lysine was incorporated into the germinative cells of the follicle bulb and the cells of the inner root sheath. Leucine and Ala were incorporated into the follicle bulb, inner root sheath, and keratinizing fiber. The incorporation of all AA into the dermal papilla was low. The relative rates of uptake of the AA into the wool follicle were as follows: L-Cys (100), L-Leu (5.5), L-Ala (2.5), and L-Lys (0.8). Uptake of Cys was saturable and followed Michaelis-Menten kinetics, suggesting a carrier-mediated system, with little or no diffusion. The majority (70%) of Cys uptake into follicles was via a Na-independent system that was not inhibited by alpha-(methyl-amino)isobutyric acid or 2-amino-2-norbonanecarboxylic acid and therefore is not via the normal Cys transport systems A, ASC, or L. Uptake of Cys appeared to be via a low-affinity, high-capacity transport system, which may be unique to the fiber-producing follicle. The majority of Ala transport had characteristics consistent with the functioning of system A (Na-dependent, inhibited by alpha-(methylamino)isobutyric acid, and low substrate affinity). Leucine uptake was inhibited by 2-amino-2-norbonanecarboxylic acid but was Na-dependent, suggesting that a variant of system L operates in the follicle to transport Leu. Lysine uptake was consistent with the operation of the usual Lys transporter system y+. Diets designed to maximize wool growth should provide AA profiles reflecting the relative rates of uptake demonstrated in this study. Investigations of possible polymorphisms in genes encoding AA transport proteins in follicles may reveal a source of genetic differences in wool growth potential among genotypes.

Intestinal function and reproductive capacity of Tegel pullets in response to exogenous oestrogen.

The effects of varying levels of exogenous oestrogen (E2) (0, 10 or 100 micrograms E2/kg BW) on the development of 18-week old pullets were tested over a 28-day period. The hormone had no significant effects on feed intake, body growth, feed conversion ratio or weight of the oviduct. Similarly, there were no significant effects of the hormone on egg production and egg weight but eggshell thickness and weight of shell per unit area were increased (P < 0.05) at a lower level of administration (10 micrograms E2/kg BW), compared to the control and the highest level of hormone. The morphometry of the jejunal mucosa and some enzymes associated with Ca transport were similar between the three groups. Oestrogen treatment, however, intensely enhanced the expression of calbindin D22K, although this was not quantified.

Body and intestinal growth of broiler chicks on a commercial starter diet. 1. Intestinal weight and mucosal development.

1. A study was conducted on the pattern of development of the intestinal mucosa of the Steggles x Ross (F1) strain of broiler chickens reared on a commercial starter diet. The mechanisms underlying the structural changes were also assessed. 2. In relation to body weight, small intestinal weight peaked at 7 d of age and declined subsequently. There was also a reduction in the relative weights of the gizzard and yolk sac with age. The length of the small intestine and its regions increased with age. 3. Crypt depth increased with age in the duodenum and jejunum while villus height increased significantly with age in all three regions of the small intestine. There were also significant changes in apparent villus surface area in the three regions, while interactions between age and intestinal region were significant in the case of crypt depth and villus height. 4. There were significant differences between the age groups in the mucosal protein content of jejunal and ileal homogenates, both tending to peak at 7 d of age. The DNA content of the intestinal mucosa declined with age in the three regions of the small intestine. While there was an increase in RNA content in the duodenum and ileum, there was a reduction in the jejunum. 5. Protein: DNA ratio increased between hatch and 21 d of age in all intestinal regions. Protein: RNA ratio decreased with age in the duodenum and ileum but increased in the jejunum. There were significant increases in RNA: DNA ratio in the duodenum and ileum but no changes were observed in the jejunum. The interactions between age and intestinal region were significant for all biochemical indices assessed. 6. At all ages, enterocyte proliferation at the jejunum was completed and quantifiable within 1 h of administration of 5-bromo-2'-deoxyuridine (BrDU). Subsequent assessment revealed an increase in crypt column count and number of BrDU-labelled cells. The rate of cell migration increased with age while there was a decline in the distance migrated in proportion to mucosal depth. The estimated life-span of enterocytes and time spent by enterocytes in the crypt varied with age. In d-old and 7-d-old chicks, migration was complete or nearly complete within 96 h of cell birth. 7. Although the intestinal mucosa of the strain was structurally developed at hatch, there was much change in structure with age, especially over the first 7 d post hatch. The rate of development was most rapid in the jejunum but the other regions are also important, on account of villus height or relative length of the region.

Body and intestinal growth of broiler chicks on a commercial starter diet. 2. Development and characteristics of intestinal enzymes.

1. Investigations were conducted into the development of intestinal enzyme function in broiler chickens on a commercial starter diet. The differences between intestinal regions and localisation of enzymes on the villus were assessed. 2. The specific activity of maltase, sucrase, aminopeptidase N (APN) and alkaline phosphatase (AP) at all intestinal sites decreased with age. There were also variations between intestinal sites although this variation depended on age. The specific activity of maltase was higher than that of the other enzymes examined, regardless of age and intestinal site. The total activities of the enzymes also increased with age at all intestinal sites. 3. Results of the localisation of enzymes on the crypt: villus axis showed that activity was expressed over a large proportion of the villus. There was an increase in the total villus activity of alpha-glucosidase (AG), APN and AP with age. Activity per unit villus surface area was similar between ages, except for jejunal AP. At hatch enzyme activity was expressed over 44.1, 55.8 and 63.3% of villus height in the duodenum, jejunum and ileum, respectively. At 21 d of age, corresponding values were 68.7, 65.6 and 77.2%. The point of peak activity from the crypt: villus junction increased with age. In the jejunum, most enterocytes were capable of secreting active enzymes within 1 h of formation. Cells maintained their secretory capabilities until they were more than 60 h old in the case of AG. 4. Although the specific activities of the enzymes were maximal at hatch, the digestive capacity of older birds may be sustained by an increase in total enzyme activity brought about by increased surface area. The pattern of enzyme activity along the gastrointestional tract (GIT) and crypt: villus axis is similar to that reported for some mammalian species.

Body and intestinal growth of broiler chicks on a commercial starter diet. 3. Development and characteristics of tryptophan transport.

1. A study was conducted to characterise the development of amino acid transport in broiler chicks, using L-tryptophan as a model. The chicks were maintained on a broiler starter diet between hatch and 21 d of age. 2. There was a significant reduction in the rate of uptake of 0.04 mM L-tryptophan with age in both the jejunum and ileum. Uptake was enhanced in the presence of 50 mM sodium chloride to different degrees depending on age and intestinal site. At both intestinal sites, uptake capacity increased with age while there was a reduction in uptake efficiency with age. 3. At a concentration of 25 mM, both sodium chloride and potasium chloride increased uptake by ileal brush-border membrane vesicles (BBMV) of 7-d-old chicks but uptake was reduced when potassium chloride was included at a concentration of 50 mM. In the presence of valinomycin, uptake by jejunal BBMV was stimulated by 25 mM sodium chloride. In the presence of both sodium chloride and potassium chloride and in the absence of valinomycin, uptake was increased by 42.6% but this was reduced to 23.4% when the ionophore was included in the buffer. 4. The Na+-independent uptake of L-tryptophan into jejunal vesicles of 21-d-old chicks was lower in the presence of D-tryptophan than in the presence of 2-aminobicyclo-[2,2,1]-heptane-2-carboxylic acid (BCH). The inclusion of BCH in the incubation medium at low concentrations significantly enhanced the uptake of 0.04 mM L-tryptophan by jejunal BBMV. 5. At similar concentration (0.04 mM) to L-tryptophan, lysine, methionine and alanine in the presence of Na+ also stimulated L-tryptophan uptake. The uptake of L-tryptophan was reduced at a higher concentration, 25 mM, of these amino acids. 6. The study revealed a decline in rate of amino acid uptake and an increase in total uptake capacity with age. Tryptophan uptake was both Na+-independent and dependent, and occurred more in the ileum than in the jejunum. The uptake of L-tryptophan depended on the concentration of other amino acids and other factors in the diet and digesta.

Activation of the gut-associated lymphoid tissue with expression of interleukin-2 receptors that peaks during weaning in the rat.

BACKGROUND: Weaning exposes the intestinal mucosa to food and bacterial antigens at an age when the immune system is believed to be immature and functionally defective. The purpose of this study was to investigate changes in activation and phenotype of immune cells of the gut-associated lymphoid tissue during weaning. METHODS: Litters of infant rats were studied from pre- to postweaned life. The activation status, assessed by interleukin-2 receptor (IL-2R) expression, and phenotype of cells in the gut-associated lymphoid tissue were examined by immunostaining. RESULTS: Interleukin-2 receptor expression peaked two to four-fold at midweaning (day 21) in mesenteric lymph nodes, jejunal lamina propria, Peyer's patches, and intraepithelial lymphocytes, compared with adult animals (day 70). CD45+ cells expanded in the lamina propria, epithelium, and lymphocyte-filled villi. With CD45 as the denominator, 10% to 50% of lymphocytes in the lamina propria and epithelium were alphabetaT-cell receptor (TCR)+, but the remaining cells had a null phenotype, because there were low numbers of gammadeltaTCR+ T cells, B cells, and macrophages. Natural killer cells peaked at midweaning in the lamina propria (9%) and epithelium (20%) but were less than 5% of CD45+ cells after weaning. CONCLUSIONS: Rather than being immature or functionally inactive, the gut-associated lymphoid tissue reacts appropriately during weaning with expression of IL-2R and expansion of alphabetaTCR+ T-cells.

Systemically but not orogastrically delivered insulin-like growth factor (IGF)-I and long [Arg3]IGF-I stimulates intestinal disaccharidase activity in two age groups of suckling rats.

The growth mitogenic properties of IGF-I on tissues of the gastrointestinal tract are well established; however, IGF effects on enzyme maturation are less clear. To test whether IGF-I peptide administration stimulates disaccharidase activity, we administered IGF-I or the more potent analog, long [Arg3]IGF-I, at doses ranging between 2 and 12.5 micrograms g-1 d-1 to suckling Wistar rat pups by either continuous s.c. infusion or by three times daily orogastric gavage. Peptides were administered for approximately 6 d starting on d 6 or 12 postpartum with six to nine rats per group. The results of the study demonstrated that systemically but not orally administered IGF-I stimulated duodenal wet tissue weight (up to 85%) and length (up to 36%). Enzyme maturation was assessed by measuring disaccharidase biochemically in tissue homogenates. Enzyme activity was also localized histocytochemically in cryostat-sectioned duodenum. After systemic infusion of IGF-I, intestinal lactase activity increased proportional to mucosal mass in both age groups. Systemic infusion of the more potent analog, long [Arg3]IGF-I, precociously induced the decline in lactase activity and accelerated the appearance of sucrase activity in the rat pups infused during the later suckling period. These findings indicate that enzyme maturation can be accelerated by systemically derived IGF-I peptides. Orogastrically IGF-I peptides, delivered at pharmacologic doses, did not affect intestinal growth or digestive enzyme maturation in suckling rat pups treated between 6 and 18 d postpartum, indicating the efficacy of IGF-I peptides may depend on the route of delivery and postnatal age of the recipient.

Systemic infusion of IGF-I or LR(3)IGF-I stimulates visceral organ growth and proliferation of gut tissues in suckling rats.

This study describes developmental changes in gastrointestinal response to insulin-like growth factor I (IGF-I) peptide administration. Neonatal rats were infused with IGF-I or long [Arg3]IGF-I (LR(3)IGF-I) for 6.5 days starting on day 6 or 12 postpartum. Peptides were delivered by mini osmotic pumps at 0, 2, 5, or 12.5 microg x g(-1) x day(-1). IGF-I infusion increased plasma IGF-I levels in both age groups but stimulated body weight gain only in the older rats. Infusion of LR(3)IGF-I did not change plasma IGF-I levels. Both peptides enhanced expression of IGF-binding proteins (IGFBP) 1 and 2 and induced IGFBP-3 in the older rats. For both age groups, weights of the kidney and spleen increased by up to 85 and 76%, respectively. IGF-I treatment also stimulated gut weight and length by up to 60 and 32%, respectively, but dose dependency was observed only in the older rats. LR(3)IGF-I was more potent for all growth parameters in both age groups. Histological observations included thickening of the mucosa and muscularis externa after infusion of IGF-I peptides. Thymidine labeling in the younger rats indicated that proliferative activity increased proportionately with crypt cell growth. These results show that IGF-I peptides selectively stimulate growth of gastrointestinal tissues in suckling rats and that the proximal gut was the most peptide-responsive region.

Determinants of lactose digestion in the miniature pig.

Although lactose is an important nutrient in the diet of the infant and child, the factors contributing to its digestion have not been clarified adequately. We sought to determine the degree to which lactase activity and small intestinal transit explain lactose digestion, the average error (SEE) in estimating lactose digestion using these parameters, and the effect of age. We compared lactose digestion from both a 7% lactose-containing formula and a solution by determining lactose in ileostomy output in pig littermates at 10 days, 4 weeks, and 10 weeks of age. The entire small intestinal mucosa was assayed for lactase specific activity (micromol x min-1 x g protein-1), total activity (micromol x min-1), and whole-villus lactase activity. Transit time (min), and transit rate (cm/min) were measured. Meal type did not affect lactose digestion. Lactose digestion was explained best by lactase specific activity (formula, R2 = 0.73, SEE = 1.1; solution, R2 = 0.69, SEE = 1.0; P < 0.001). The next best parameter was total transit rate (formula, R2 = 0.69, SEE = 2.0; solution, R2 = 0.46, SEE = 1.3). The relationship with lactase specific activity was age related and there appeared to be a critical value of lactase specific activity above which essentially all the lactose was digested.

Role of thyroid hormones in early postnatal development of skeletal muscle and its implications for undernutrition.

Energy intake profoundly influences many endocrine axes which in turn play a central role in development. The specific influence of a short period of mild hypothyroidism, similar to that induced by undernutrition, in regulating muscle development has been assessed in a large mammal during early postnatal life. Hypothyroidism was induced by providing methimazole and iopanoic acid in the feed of piglets between 4 and 14 d of age, and controls were pair-fed to the energy intake of their hypothyroid littermates. Thyroid status was evaluated, and myofibre differentiation and cation pump concentrations were then assessed in the following functionally distinct muscles: longissimus dorsi (l. dorsi), soleus and rhomboideus. Reductions in plasma concentrations of thyroxine (T4; 32%, P < 0.01), triiodothyronine (T3; 48%, P < 0.001), free T3 (58%, P < 0.001) and hepatic 5'-monodeiodinase (EC 1.11.1.8) activity (74%, P < 0.001) occurred with treatment. Small, although significant, increases in the proportion of type I slow-twitch oxidative fibres occurred with mild hypothyroidism, in l. dorsi (2%, P < 0.01) and soleus (7%, P < 0.01). Nuclear T3-receptor concentration in l. dorsi of hypothyroid animals compared with controls increased by 46% (P < 0.001), a response that may represent a homeostatic mechanism making muscle more sensitive to low levels of circulating thyroid hormones. Nevertheless, Na+, K(+)-ATPase (EC 3.6.1.37) concentration was reduced by 15-16% in all muscles (l. dorsi P < 0.05, soleus P < 0.001, rhomboideus P < 0.05), and Ca(2+)-ATPase (EC 3.6.1.38) concentration was significantly reduced in the two slow-twitch muscles: by 22% in rhomboideus (P < 0.001) and 23% in soleus (P < 0.05). It is concluded that during early postnatal development of large mammals a period of mild hypothyroidism, comparable with that found during undernutrition, induces changes in myofibre differentiation and a down-regulation of cation pumps in skeletal muscle. Such changes would result in slowness of movement and muscle weakness, and also reduce ATP hydrolysis with a concomitant improvement in energetic efficiency.

Nutritional modulation of insulin-like growth factor-I expression in early postnatal piglets.

The roles of intrauterine growth retardation, energy intake, and food composition in determining circulating and hepatic concentrations of IGF-I in early postnatal life have been determined. Intrauterine growth-retarded, small-for-gestational-age piglets were kept at thermal neutrality and fed sow's milk replacement formula to repletion at 6-h intervals between 2 and 14 d of age. When their appropriate-for-gestational-age littermates were pair-fed this intake, there were no significant differences in plasma or hepatic concentrations of IGF-I. Thus, under conditions of controlled food intake, prenatal undernutrition does not affect the postnatal expression of IGF-I. However, when appropriate-for-gestational-age piglets were fed to repletion at 6-h intervals over the 12 d, they had a significantly greater hepatic IGF-I concentration (p < 0.002) and food intake (p < 0.001) than the small-for-gestational-age piglets, indicating a critical role for food intake regulation in catch-up growth. Striking differences in growth rate and IGF-I expression were also found between formula-fed, appropriate-for-gestational-age piglets compared with animals left with the sow. The latter grew much more rapidly (p < 0.0001) and had considerably higher levels of plasma IGF-I (p < 0.0001) despite similar hepatic IGF-I concentrations. Differences in plasma IGF-I may have been caused by the high level of IGF-I in maternal milk, by differences in hepatic synthesis and release, or by altered profiles of IGF binding proteins and hence in altered IGF-I clearance from plasma.(ABSTRACT TRUNCATED AT 250 WORDS)

Differential effects of lipid and carbohydrate on enterocyte lactase activity in newborn piglets.

The influence of enteral feeding in the neonate on lactase-phlorizin hydrolase activity in the small intestine has been determined in newborn piglets fed a series of modified colostra, with a controlled metabolizable energy intake, during the first 31.5 h of life. Striking differences were observed between lactase specific activity in mucosal homogenates and enterocyte lactase activity along the villus axis; compared with newborns, the former decreased after feeding colostrum, whereas the latter increased significantly. When lipid was present in adequate amount, the increase in enterocyte lactase activity occurred when carbohydrate was present as either lactose or galactose. However, when the lipid content of the diet was low, there was a specific effect of carbohydrate composition which was dependent on position along the villus axis: in the lower villus, colostra high in lactose or glucose stimulated an increase in lactase, but there was no such effect with a high galactose intake. It is concluded that colostrum increases enterocyte lactase activity during the first day of life, and that this is dependent on both the nutrient composition of the diet and the position of the enterocytes along the villus.

Administration of 3,5,3'-triiodothyronine induces a rapid increase in enterocyte lactase-phlorizin hydrolase activity of young pigs on a low energy intake.

The rapid increase in plasma concentration of 3,5,3'-triiodothyronine (T3) which occurs after feeding may invoke changes in lactase-phlorizin hydrolase (LPH) activity of the small intestine. This hypothesis has been tested in 6-week-old pigs living at thermal neutrality (26 degrees C) on a low level of energy intake. Littermate pairs were infused with either saline or T3 at 30 min intervals over a 6 h period, 18-24 h after the last meal. The activity of LPH in mucosal homogenates increased significantly in test compared with control animals (P < 0.05; T3 37% > saline). This was a specific effect on LPH since there was no effect of T3 on the activity of sucrase-isomaltase. Further, it could not be attributed to changes in intestinal morphology since there were no differences in crypt depth, villus height or villus area between the two groups. Enzyme-cytochemical analysis indicated that administration of T3 increases LPH activity at all points along the villus axis, whereas there is no effect on alpha-glucosidase (combined sucrase-isomaltase and maltase) activities. These results indicate that there is unlikely to be a simple causal relation between the immediate increase in plasma T3 after feeding and the initial decline in LPH activity observed previously in young pigs living in a cold environment. By contrast, the subsequent increase in LPH activity could be under the direct control of the food-induced increase in plasma T3 concentration, and the present results suggest a potential role for T3 as an important short-term homeostatic regulator of LPH in the small intestine.

Genetic regulation of enterocyte function: a quantitative in situ hybridisation study of lactase-phlorizin hydrolase and Na(+)-glucose cotransporter mRNAs in rabbit small intestine.

The enterocyte undergoes sequential changes in its structure and function as it migrates rapidly from the small intestinal crypts to the villus tip. The mechanisms by which these changes are regulated "in tune" with ontogenic and dietary changes in the luminal environment are currently under investigation. This study has employed oligonucleotide probes to follow the expression of the lactase-phlorizin hydrolase (LPH) and Na(+)-glucose cotransporter (SGLT1) genes in rabbit small intestine using quantitative in situ hybridisation histochemistry. The profiles of LPH mRNA and SGLT1 mRNA accumulation along the crypt-villus axis were found to be very similar. Although mRNA was undetectable in the crypt. LPH and SGLT1 mRNA levels rose rapidly at the crypt-villus junction, reaching a maximum between 210 microns and 330 microns above this point. Further up the villus the level of mRNAs declined. SGLT1 mRNA was present in all small intestinal segments (duodenum, jejunum and ileum), whereas LPH mRNA was absent from the ileum. LPH activity rose and fell in conjunction with mRNA, but SGLT1 activity was greatest at the villus tip where mRNA levels were considerably reduced. These data have been used to discuss the genetic regulation of enterocyte differentiation and function.

The effect of hyperosmotic challenge upon ion transport in cultured renal epithelial layers (MDCK).

Exposure of the basal-lateral surfaces of MDCK epithelia, mounted in Ussing chambers, to medium made hyperosmotic by the non-electrolyte mannitol, resulted in a marked inhibition of the adrenaline-stimulated inward short-circuit current (Cl- secretion). This inhibition was unaccompanied by a reversal of the adrenaline-stimulated increment in tissue conductance, indicating that the inhibition was due to modulation of ion transport at the basal-lateral membranes. Loop-diuretic-sensitive 86Rb(K+) efflux mediated by the Na+ - K+ -2 Cl- cotransporter at the basal-lateral membranes was markedly stimulated by hypertonic exposure. A diuretic-sensitive K+ (Cl-) loss was observed in shrunken cells upon prolonged exposure (20 min), showing that the net direction of "cotransport" flux was outward. 86Rb(K+) efflux stimulated by adrenaline (100 microM), exogenous ATP (100 microM) and A23187 (10 microM) was attenuated in shrunken cells, suggesting that basal-lateral K+ conductance is reduced in hyperosmotic media. "Cotransport" stimulation by hyperosmotic medium was asymmetric, apical bathing hypertonicity being ineffective. These data are consistent with a low hydraulic permeability of the apical membranes.