An in situ single-pass perfusion model for assessing absorption across the intestinal mucosa of the brushtail possum

AIM: To develop an in situ animal model for assessing absorption of molecules across the intestinal mucosa of possums.

METHODS: A surgical preparation was used to perfuse known concentrations of reference compounds (fluorescein and luteinising hormone-releasing hormone; LHRH) through measured sections of selected regions (jejunum, caecum, proximal colon) of the intestinal tract of 19 possums, over a 2-h period. Plasma concentrations of the compounds, which were perfused either with or without co-administration of a permeation enhancer (sodium deoxycholic acid; SDA), were determined in the perfusion effluent, peripheral and in some instances in the pre-hepatic circulation by spectrofluorometry (fluorescein) or radio-immunoassay (LHRH). Pharmacokinetic parameters of both compounds in the possum were determined over a period of up to 4 h in a further 30 animals (fluorescein, n=6; LHRH n=24), from their plasma profiles following intravenous (I/V) administration of a bolus dose.

RESULTS: In animals perfused with 25 mg/ml fluorescein (Perfusion Experiment (PE) 1), the mean plasma concentration was 2.8 (SE 0.12) µg/ml in post-hepatic blood samples. When possums were perfused with 2.5 mg/ml fluorescein and 7 µg/ml LHRH (PE 2), mean plasma concentrations were 0.3 (SE 0.01) and 7.8 (SE 1.64) µg/ml fluorescein and 0.1 (SE 0.02) and 6.3 (SE 0.45) ng/ml LHRH, in the absence and presence of permeation enhancer, respectively. There was a poor correlation between pre-hepatic and post-hepatic concentrations.

CONCLUSIONS: The single-pass in situ perfusion technique provided a useful model for investigating basic information on the absorption of biocontrol agents across the intestinal tract of possums, but had limitations that must be recognised.     

Solar constant: first direct measurements

The solar constant was directly measured from an altitude of about 82 kilometers-apparently the first such determination. The total solar intensity was 136.1 milliwatts per square centimeter, or 1.952 calories per square centimeter, per minute-about 2.5 percent less than Johnson's derived value. Energy in the ultraviolet and visible regions (for lambda less than 607 nanometers) was 7.0 percent less than that obtained by integration over Johnson'Scurve; for integral flux of lambda greater than 607 nanometers there was almost perfect agreement. Seven supporting series of measurements from lower altitudes agreed extremely well with these results after correction for atmospheric extinction.     

Survival,cold tolerance and seasonality of infection of European horse chestnut (Aesculus hippocastanum) by Pseudomonas syringae pv. aesculi

Bleeding canker of European horse chestnut, caused by the pathogenic bacterium Pseudomonas syringae pv. aesculi (Pae), is now an established disease throughout several countries in northwest Europe after first emerging in 2001–2002. Pae infects the woody branches of horse chestnut directly via natural discontinuities in the bark, such as lenticels, leaf scars and leaf traces, and nodes. However, the timing of infection in relation to seasonality of host development, and the dispersal mechanisms of Pae, in particular its ability to survive and spread in soil and water, remains unknown. In this study, infection of freshly cut horse chestnut shoots by Pae was assessed at monthly intervals over a 12 month period. Pae infected the greatest numbers of lenticels and leaf scars of horse chestnut when inoculated onto actively elongating shoots in spring and early summer, whereas lesion extension from artificial wound sites was greatest after inoculation during early dormancy. Soil survival experiments showed that Pae was still detectable and viable after 50 weeks' incubation in sterile soil and 41 weeks' incubation in nonsterile soil in the absence of host debris. Pae also remained viable and pathogenic after 1 year's storage in King's B broth at ?20 and ?80°C, and was not killed by freeze/thaw treatments. Thus Pae is able to survive independently for extended periods in soil and water, and can tolerate lengthy periods of freezing at very low temperatures. Such information may facilitate a greater understanding of the epidemiology and spread of Pae in northern Europe.     

Single layer centrifugation of fresh dromedary camel semen improves sperm quality and in vitro fertilization capacity compared with simple sperm washing

Single layer centrifugation (SLC) through a colloid is a tool for selecting viable mammalian spermatozoa but has not been used previously for fresh dromedary camel sperm. Semen from six camels (2 ejaculates/male) was diluted 1:5 (v:v) or 1:10 (v:v) in a Tris–citrate–fructose buffer for mechanical liquefaction by gentle pipetting. Following liquefaction, semen was processed either by SLC or by centrifugation without a colloid (control). Total and progressive motilities, CASA kinematics, vitality and acrosome integrity (eosin–nigrosin) and plasma membrane integrity (Hypo‐osmotic swelling test; HOST), and fertilizing ability in a heterologous assay (zona‐free goat oocytes) were evaluated. Both total (p = .003) and progressive motilities (p = .003) were higher in SLC‐processed than in control semen samples, irrespective of dilution. Positive HOST values increased when using colloid in 1:5 (p = .001) and 1:10 dilution (p = .010). Colloid‐selected sperm had higher penetration rates than controls (p < .001 and p = .02 for 1:5 and 1:10 dilutions, respectively). However, only the SLC sperm at 1:5 dilution showed higher percentages of pronuclear formation (p = .02) than controls. Dilution effect was only significant for total motility before in vitro fertilization, with higher values for the 1:5 dilution (p = .033). The recovery rates of motile sperm between dilutions were similar (26.1% vs 35.4%; p = .226). In conclusion, SLC is a promising tool for selecting functional dromedary camel sperm and warrants more research.