Concentration dependence of protein permeability across the canine visceral pleura

Water and protein movement across the pulmonary endothelial-visceral pleural membrane of spontaneously breathing anesthetized dogs was analyzed to determine if the protein concentration at the microvascular membrane (Cpro) influences microvascular permeability. The left lung was enclosed in a water-impermeable membrane, creating a visceral pleural space (VPS); fluid and solute fluxes were determined as the filtration or reabsorption of water and protein in the VPS. The plasma protein concentration was experimentally varied by plasmapheresis with saline replacement while the pleural fluid protein concentration was varied by introducing different concentrations of plasma mixed with saline into the VPS. Hydrostatic pressures were maintained within a physiologic range (pulmonary capillary pressure 12.1-16.1 mm Hg). The plasma protein concentration fell as low as 1.98 g/dl, and Cpro, calculated as the mean of the plasma and pleural fluid protein concentrations, ranged from 1.73 to 6.23 g/dl. The relationship between Cpro and the apparent homoporous diffusional permeability for protein (Phs), Phs(cm/sec X 10(-6] = 0.95 Cpro (g/dl) + 2.28, was highly significant (r = 0.87, P less than 0.01). In contrast, the hydraulic conductivity was not affected by a reduction in Cpro to this level (r = 0.21, P greater than 0.4). Although the solute concentration at the endothelial membrane should be considered when evaluating changes in protein permeability, under most experimental conditions the magnitude of this effect will be small.     

Involvement of CD31 in lymphocyte-mediated immune responses: importance of the membrane-proximal immunoglobulin domain and identification of an inhibiting CD31 peptide

CD31 (PECAM-1) is an immunoglobulin gene superfamily cell adhesion molecule found on vascular endothelium, platelets, and leukocytes. Lymphocyte expression of CD31 is most closely associated with the CD45RA+CD8+ naive T phenotype. CD31 has recently been shown to play a role in leukocyte egress to inflammatory sites. The mechanism of CD31 adhesion remains under investigation. Several investigators have reported evidence for a heterotypic ligand. We have previously shown that CD31 is phosphorylated with cell activation, which suggests a possible role for CD31 in cell activation events. We therefore studied the effects of CD31 antibodies on in vitro assays of lymphocyte activation. One CD31 antibody, LYP21, inhibited the mixed lymphocyte reaction (MLR) in a specific and dose-dependent fashion. An LYP21 epitope was localized to the sixth Ig domain of CD31. This peptide and a scrambled control peptide were synthesized and used to study effects of this epitope on lymphocyte activation. The CD31 peptide strongly inhibited the MLR. Because CD31 is expressed on both stimulator and responder populations, stimulator peripheral blood leukocytes and responder lymphocyte populations were separately incubated with CD31 peptide or control peptide and then washed before mixing. The CD31 peptide inhibited the MLR equally when either stimulator or responder cells were preincubated with the CD31 peptide. We further sorted responder cells into CD31-high and CD31-low populations and separately incubated these subsets with peptides. The CD31 peptide strongly inhibited MLRs, regardless of level of responder-cell CD31 expression. Examination of MLR reactions involving the CD31 peptide showed dispersed small aggregates of cells, rather than the single large aggregate observed in control MLRs. The CD31 peptide did not affect activation of lymphocytes by phorbol myristate acetate (PMA) and ionomycin. These results suggest that a surface CD31-ligand interaction may have a functional role in alloimmune lymphocyte activation and identify a functionally important domain of CD31.     

Randomized study of percutaneous endoscopic gastrostomy versus nasogastric tubes for enteral feeding in head and neck cancer patients treated with (chemo)radiation

Percutaneous endoscopic gastrostomy (PEG) tubes have largely replaced nasogastric tubes (NGT) for nutritional support of patients with head and neck cancer undergoing curative (chemo)radiotherapy without any good scientific basis. A randomized trial was conducted to compare PEG tubes and NGT in terms of nutritional outcomes, complications, patient satisfaction and cost. The study was closed early because of poor accrual, predominantly due to patients’ reluctance to be randomized. There were 33 patients eligible for analysis. Nutritional support with both tubes was good. There were no significant differences in overall complication rates, chest infection rates or in patients’ assessment of their overall quality of life. The cost of a PEG tube was 10 times that of an NGT. The duration of use of PEG tubes was significantly longer, a median 139 days compared with a median 66 days for NGT. We found no evidence to support the routine use of PEG tubes over NGT in this patient group.     

Regulation of activin A, inhibin A, and follistatin production in human amnion and choriodecidual explants by inflammatory mediators

OBJECTIVE: To determine the effects of inflammatory mediators on the production of activin A, inhibin A, and the binding protein follistatin in term amnion and choriodecidual tissues. METHODS: The effects of interleukin-1 beta (IL-1 beta; 1 ng/mL), tumor necrosis factor-alpha (TNF-alpha; 10 ng/mL), and bacterial lipopolysaccharide (LPS; 5 microg/mL) on production rates of activin A, inhibin A, and follistatin by term choriodecidual and amnion membranes in explant culture were determined using specific enzyme-linked immunoabsorbent assays. RESULTS: All explants (n = 6 placentas) produced detectable amounts of activin A, inhibin A, and follistatin under basal conditions; choriodecidual production rates were more than tenfold higher than amnion rates. In amnion explants, activin A production was stimulated by IL-1 beta and TNF-alpha to 450 +/- 155.4% and 531 +/- 170.8% of control, respectively (mean +/- standard error of the mean; P <.05 by analysis of variance), whereas production of inhibin and follistatin was stimulated to a much more modest extent. Similar responses were observed in the choriodecidual explants. Lipopolysaccharide had no significant effect on amnion activin A production, but stimulated choriodecidual production to 290 +/- 34% of control. Lipopolysaccharide exerted only limited effects on inhibin A and follistatin production. CONCLUSIONS: Treatment with proinflammatory mediators resulted in a preferential increase in activin A production compared with that of inhibin A or follistatin. These findings suggest that inflammation of the gestational membranes could result in increased local activin A production and bioactivity.     

Maternal serum total activin A and follistatin in pregnancy and parturition

Objective To examine changes in maternal serum levels of activin A and follistatin during pregnancy and labour
Design In three cross sectional and three longitudinal studies venous blood was collected from women during pregnancy, spontaneous labour, labour induction and prior to elective caesarean section for the measurement of activin A and follistatin.
Setting Monash Medical Centre, Clayton, Victoria, Australia.
Population One hundred and twenty-three women participated in a cross sectional study in pregnancy, 18 women in two longitudinal pregnancy studies, 36 women in a cross sectional labour study, nine women in a longitudinal study of labour induction. Ten women undergoing elective caesarean section were also studied.
Methods Activin A and follistatin were measured using two sensitive and specific enzyme-linked immunosorbent assays.
Results In the cross sectional study of pregnancy, mean (SEM) maternal serum activin A and follistatin levels increased towards term (2.4 ng/mL (0.3) and 1.8 ng/mL (0.3) in first trimester to 18.9 ng/mL (3.8) and 5.3 ng/mL (0.9) at term, respectively), but the longitudinal study revealed that levels plateau in the last three weeks of pregnancy (16.0 ng/mL (2.6) and 6.2 ng/mL (1.4) at 37 weeks and 16.6 ng/mL (3.5) and 6.2 ng/mL (0.5) before labour for activin A and follistatin, respectively). There was no difference in levels of activin A and follistatin between women delivered by caesarean section and labouring women at term (14.9 ng/mL (2.8) vs 11.0 ng/mL (0.93) and 5.95 ng/mL (0.67) vs 5.71 ng/mL (0.63), respectively) and levels of both proteins did not alter throughout spontaneous or induced labour.
Conclusions We believe that these data argue against activin A playing an acute role in the initiation or regulation of human parturition.     

Release of activin and follistatin during cardiovascular procedures is largely due to heparin administration

Recent evidence has suggested that activin A complexed to its binding protein, follistatin, may be present on the surface of cells through their interaction with heparan sulfate proteoglycans. As heparin is used routinely in many cardiovascular procedures for its anticoagulation properties, it may also cause the release of heparin-binding growth factors, including activin and follistatin, from the vascular endothelium. We examined the effect of two cardiovascular procedures and the use of heparin directly on the circulating concentrations of activin A and follistatin. A rapid and robust release of activin A and follistatin occurred in the circulation of patients undergoing abdominal aortic aneurysm repair or carotid endarterectomy at the time of vessel clamping and administration of heparin (5000 IU). This release pattern was dissimilar to that of the inflammatory marker, interleukin-1beta. However, administering heparin (2500 IU) to coronary angiography patients produced a similar activin and follistatin response, whereas placebo-treated angiography patients had no response. These findings illustrate that the routine use of heparin in surgical procedures elicits a rapid and robust release of activin and follistatin. This has direct clinical relevance by potentially activating heparin-binding growth factors that are important in injury, hyperplasia, and restenosis of vessels.