The design and implementation of an off-the-shelf, standards-based tele-ultrasound system.

We developed an off-the-shelf system to transfer DICOM-compliant ultrasound images from a small rural hospital in northern Alberta to an urban radiology clinic in Calgary. The transfer time was less than 30 s per image. The radiologist could then review the case and release the patient. The radiologist could also switch to realtime videoconferencing mode and direct the rural ultrasound technician to obtain additional images of the patient.

Atrial natriuretic peptide-induced secretory responses in rabbit vs rat ileum.

The aim of this study was to characterize and compare the effect of atrial natriuretic peptide (ANP) on ileal transport function in two common laboratory animals, the Hooded-Lister rat and the New Zealand White rabbit. ANP 1 microM produced a maximal increase in short circuit current (Isc) that was Cl- dependent in both rat and rabbit. The maximal response in rat tissue was twice the magnitude of that seen in the rabbit. Furthermore, the rabbit Isc response was rapid and transient compared with that of the rat. In both rats and rabbits, the ANP response was dependent on extracellular Ca++. Neural blockade had no effect on the rat ANP response but significantly inhibited the ANP response in rabbits. In the rat, the effect of ANP is mediated by seratonin (5-HT) acting through 5-HT2 receptors. In contrast, no role for 5-HT could be seen in the rabbit ileal ANP response. In intact tissue in both rat and rabbit, ANP stimulated a significant rise in cGMP levels. ANP had no effect on cAMP levels in either species. The findings suggest a separate and distinct mechanism for ANP-mediated intestinal Cl- secretion in the rat ileum compared with the rabbit.

Role of ornithine decarboxylase in enterocyte mitochondrial function and integrity.

We examined the role of ornithine decarboxylase (ODC) and polyamine biosynthesis in regulating mitochondrial function and integrity along the crypt-villus axis in male Sprague-Dawley rats. Isolated villus tip enterocytes from control rats demonstrated a greater cellular capacity for glucose oxidation than crypt enterocytes. Mitochondrial enzyme activities were similar along the crypt-villus axis. The role of ODC was assessed by treating experimental rats with the irreversible ODC inhibitor alpha-difluoromethylornithine (DFMO) for 24 h. Animals receiving DFMO demonstrated a decreased CO2 production from [2-(14)C]pyruvate along the entire crypt-villus axis coupled with an increase in lactate production in the upper cell populations. CO2 production from [14C]glucose and total ATP levels were not affected by DFMO treatment. Ultrastructural examination revealed localized mitochondrial swelling and bursting only in enterocytes corresponding to the population of cells newly emerged from the crypt during DFMO treatment. In DFMO-treated animals, 2 microM spermine completely prevented the structural mitochondrial injury and restored the metabolic crypt-villus gradient. These results suggest that as enterocytes migrate from the crypt up the villus, mitochondrial function increases to handle the increased metabolic demands placed on the cell by nutrient absorption. ODC activity and polyamines are necessary for this increased mitochondrial function and have a role in the maintenance of mitochondrial integrity in maturing enterocytes migrating from the crypt onto the villus.

Intestinal secretory response to atrial natriuretic peptide during postnatal development in the rabbit.

The postnatal development of atrial natriuretic peptide (ANP) stimulus-secretion coupling was examined in rabbit ileum. A positive correlation between age and ANP-induced secretory responsiveness was observed. The short circuit current (Isc) response in 14-day animals was significantly (p < 0.05) less than that seen in 21-day, 28-day and adult animals. Animals at 21 days of age were less responsive (p < 0.05) than either 28-day or adult animals which did not differ. The Isc response of infant animals (day 14) to the Cl- secretagogue 3-isobutyl-1-methylxanthine was blunted in the infant, as was the response to electrical field stimulation. The infant animals had higher basal levels of mucosal cGMP, but were still able to respond to ANP with an elevation in cGMP. The ability of the immature ileum to generate the second messenger molecule cGMP in response to ANP, but not to produce an appropriate Isc response to ANP, indicates infant animals possess underdeveloped secretory mechanisms and lack the ability to effectively couple secretory stimuli to a secretory response.

Polyamines alter intestinal glucose transport.

Polyamines are required for the growth of all eukaryotic cells. Enterocytes respond to luminal nutrients with large increases in polyamine synthesis, even though they are mature, nonproliferating cells. The role of polyamines in these cells is unknown. The current experiments examined whether polyamines affected intestinal transport of glucose, since absorption is the primary activity of enterocytes and since polyamines are known to affect membrane function and stability. Glucose transport was examined in rabbit brush-border membrane vesicles (BBMV). BBMV from rabbits given 5% alpha-difluoromethylornithine (DFMO) in their drinking water 24 h before they were killed transported significantly less glucose than control vesicles [38% decrease in maximal transport rate (Jmax)]. Orogastric administration of spermine, spermidine, or putrescine to DFMO-treated animals 24 h before they were killed prevented the decrease. In rabbits receiving only orogastric spermine, glucose transport was significantly increased (64% increase in Jmax), whereas in vivo spermidine and putrescine decreased Jmax. This increase in Jmax caused by in vivo administration of spermine was not dependent on protein synthesis. Addition of polyamines whether in vivo or in vitro decreased Michaelis constant in vesicles from control and DFMO-treated animals. The change in glucose transport induced by DFMO or polyamines was not related to altered membrane lipid composition or fluidity.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of malnutrition on microvillus membrane glucose transport and physical properties.

We examined sodium-dependent glucose transport, membrane lipid composition, and membrane fluidity in microvillus membrane vesicles isolated from the distal intestine of infant rabbits subjected to protein-energy malnutrition and age-matched controls. In vesicles from malnourished animals, sodium-dependent glucose transport was significantly enhanced, as evidenced by a twofold increase in maximal transport capacity, Jmax. Carrier affinity for glucose, as assessed by the Km of the transport process, was unaffected. These alternations were associated with marked changes in microvillus membrane composition. Malnourished animals had an increase in the lipid-to-protein ratio of the microvillus membrane, which suggests that malnutrition might be associated with either a reduction in membrane protein or an increase in membrane lipid. This would be expected to increase the fluidity of the microvillus membrane. However, we observed no differences in either the static or dynamic component of membrane fluidity, using multiple fluorescent probes, between dietary groups. Further analysis of membrane lipids was undertaken to establish whether quantitative differences in lipid subclasses could explain this discrepancy. We found that nutrient deprivation produced numerous alterations in membrane lipids. The major findings were an increase in both the cholesterol-to-phospholipid and phosphatidylethanolamine-to-phosphatidylcholine ratios. Both alterations would be expected to decrease membrane fluidity and presumably represent a compensatory response to the loss of membrane protein. Thus chronic postnatal protein-energy malnutrition initiates several adaptive responses that include major alterations in the chemical composition of the microvillus membrane. The resulting effect preserves efficient glucose transport and maintains the physical properties of the microvillus membrane.