Shear-induced platelet aggregation requires von Willebrand factor and platelet membrane glycoproteins Ib and IIb-IIIa

Different types of platelets in various types of plasma were subjected to levels of shear stress that produce irreversible platelet aggregation in normal platelet-rich plasma (PRP). At shear stresses of 90 or 180 dyne/cm2 applied for 30 seconds or five minutes, aggregation was either absent or only transient and reversible using severe von Willebrand's disease (vWD) PRP (less than 1% von Willebrand factor, vWF); Bernard-Soulier syndrome (BSS) PRP (platelets deficient in the membrane glycoprotein Ib, GPIb); normal PRP plus monoclonal antibody (MoAb) to GPIb; thrombasthenic PRP (platelets deficient in membrane glycoprotein IIb-IIIa complex, GPIIb-IIIa); and normal PRP plus MoAb to GPIIb-IIIa. Shear-induced aggregation was inhibited under the above conditions, even though the platelets were activated to release their granular contents. Sheared normal platelets in vWD plasma aggregated in response to added vWF. These studies demonstrate that the formation of stable platelet aggregates under conditions of high shear requires vWF and the availability of both GPIb and GPIIb-IIIa on platelet membranes. The experiments demonstrate that vWF-platelet interactions can occur in the absence of artificial agonists or chemical modification of vWF. They suggest a possible mechanism for platelet aggregation in stenosed or partially obstructed arterial vessels in which the platelets are subjected to relatively high levels of shear stress.     

Membrane conductance and cell volume changes evoked by vasoactive intestinal polypeptide and carbachol in small intestinal crypts

We have used the perforated-patch whole-cell recording mode of the patch-clamp technique to monitor membrane potential and measured cell volume changes by image analysis, to determine the nature of the response to secretagogues of isolated whole guinea-pig small-intestinal crypts. Vasoactive intestinal polypeptide (VIP) produced a dose-dependent depolarisation (EC₅₀=30 nM) and an increase in membrane conductance that could be potentiated by carbachol. Similar depolarisations were observed with forskolin. The depolarisation induced by 100 nM VIP was smaller when pipette [Cl^–] was 60 mM than when it was 145 mM, suggesting an effect through Cl^– conductance activation. Carbachol alone produced a hyperpolarisation (EC₅₀=2 M). The Cl^– channel blocker 5-nitro-2-(3-phenylpropylamino)-benzoic acid (NPPB) produced a small hyperpolarization. When VIP was added in the presence of NPPB, the depolarising effect of the peptide was abolished and a hyperpolarisation was observed instead, consistent with the parallel activation of a K⁺ conductance. Both carbachol (100 M) and VIP (100 nM) induced a 25%–30% shrinkage of crypts, which was maximal 8 min after addition of the secretagogue. The induced shrinkage was sustained in the continued presence of agonist and was reversed upon washout. Shrinkage induced by the agonists was abolished by increasing extracellular K⁺ from 6 mM to 20 mM and was inhibited partially in the presence of 100 M anthracene-9-carboxylic acid in the bath. The decrease in volume induced by 100 nM VIP was totally abolished in the presence of 100 M NPPB. The results are consistent with the view that both VIP and carbachol induce secretion in small-intestinal crypts. This would lead to a net loss of K⁺ and Cl^– ions from the cytoplasm with a concomitant decrease in cell volume.     

Immunohistochemical testing of conventional adenomas for loss of expression of mismatch repair proteins in Lynch syndrome mutation carriers: a case series from the Australasian site of the colon cancer family registry

Debate continues as to the usefulness of assessing adenomas for loss of mismatch repair protein expression to identify individuals with suspected Lynch syndrome. We tested 109 polyps from 69 proven mutation carriers (35 females and 34 males) belonging to 49 Lynch syndrome families. All polyps were tested by immunohistochemistry for four mismatch repair proteins MLH1, MSH2, MSH6 and PMS2. Detailed pathology review was performed by specialist gastrointestinal pathologists. The majority of polyps (86%) were conventional adenomas (n=94), with 65 tubular and 28 tubulovillous adenomas and a single villous adenoma. The remaining 15 lesions (14%) were serrated polyps. Overall, loss of mismatch repair expression was noted for 78/109 (72%) of polyps. Loss of mismatch repair expression was seen in 74 of 94 (79%) conventional adenomas, and 4 of 15 (27%) serrated polyps from mismatch repair gene mutation carriers. In all instances, loss of expression was consistent with the underlying germline mutation. Mismatch repair protein expression was lost in 27 of 29 adenomas with a villous component compared with 47 of 65 adenomas without this feature (93 vs 73%; P=0.028). A strong trend was observed for high-grade dysplasia. Mismatch repair deficiency was observed in 12 of 12 conventional adenomas with high-grade dysplasia compared with 60 of 79 with low-grade dysplasia (100 vs 76%; P=0.065). We were unable to demonstrate a significant association between conventional adenoma size or site and mismatch repair deficiency. All (4/4 or 100%) of the serrated polyps demonstrating mismatch repair deficiency were traditional serrated adenomas from a single family. Diagnostic testing of adenomas in suspected Lynch syndrome families is a useful alternative in cases where cancers are unavailable. The overwhelming majority of conventional adenomas from mutation carriers show loss of mismatch repair protein expression concordant with the underlying germline mutation.     

Alcohol‐induced respiratory symptoms improve after aspirin desensitization in patients with aspirin‐exacerbated respiratory disease

Background

Aspirin‐exacerbated respiratory disease (AERD) is characterized by chronic eosinophilic rhinosinusitis, nasal polyps, asthma, and respiratory sensitivity to aspirin and nonsteroidal anti‐inflammatory drugs (NSAIDs). In addition to sensitivity to aspirin and NSAIDs, the majority of patients with AERD have been reported to have respiratory intolerance associated with the consumption of alcohol.

Methods

A multicenter prospective cohort study was performed. Patients with AERD confirmed by aspirin challenge were eligible to participate. Those who described themselves as able to tolerate alcohol consumption were excluded. Patients underwent aspirin desensitization following endoscopic sinus surgery. A questionnaire was distributed to patients before and after desensitization to determine pre‐desensitization and post‐desensitization symptoms associated with alcohol ingestion.

Results

Forty‐five patients were enrolled and 37 patients completed the study. The most common pre‐desensitization symptoms were nasal congestion (95.6%), rhinorrhea (46.7%), and wheezing (40%). Improvement in the ability to tolerate alcohol was noted in 86.5% of participants (95% confidence interval [CI], 75.5% to 97.5%) and 70.3% of participants (95% CI, 55.5% to 85.0%) described desensitization to be “very helpful” or “extremely helpful” for their ability to tolerate alcohol.

Conclusion

The majority of patients with AERD who experience respiratory symptoms with alcohol consumption describe improvement in this domain following aspirin desensitization.

     

The Effects of in Vivo Pulmonary Oxygenation on Lung Liquid Production in Near-Term Fetal Sheep

Lung liquid (LL) is secreted into the fetal lung lumen, but it must be rapidly absorbed at birth to allow air breathing. In vitro studies have implicated oxygen as a possible factor causing the switch from secretion to absorption of lung liquid at birth. We developed a technique of oxygenating the fetal lung using liquid ventilation with haemoglobin (Hb) solutions in chronically catheterized fetal lambs (129-140 days gestation; term, 147 days). In some experiments 2,3-diphosphoglycerate (DPG) was added to increase oxygen delivery. LL secretion rate (Jv) was measured using an indicator dilution method. Eighteen fetuses were divided into four groups and ventilated with liquid under the following conditions: (i) Hb with oxygen, (ii) Hb without oxygen, (iii) Hb with DPG and oxygen and (iv) Hb and DPG without oxygen. There was a significant rise (2.6 mmHg, P < 0.02) in fetal arterial Po2 in group iii, but in none of the other groups. In the first 3 h of liquid ventilation there was no difference in Jv between the groups. In group i, during hours 4-6 of liquid ventilation, there was a significant rise in secretion rate from 2.25 +/- 0.88 to 3.74 +/- 0.85 ml h-1 kg-1 (P < 0.001). In group iii, when comparing Jv in the first 3 h of liquid ventilation with that in the following 3 h period of liquid ventilation, a strong trend towards reduction in secretion was observed, falling from 3.03 +/- 0.65 to 0.74 +/- 0.92 ml h-1 kg-1 (three of the four experiments showed a significant decrease in Jv in hours 4-6). These experiments indicate that oxygen delivered to the fetus using liquid ventilation with haemoglobin solutions leads to increased LL secretion when oxygen delivery is small, and suggest there is a decrease in secretion with greater oxygen delivery to the lung.