Influence of the vascular endothelium on angiotensin II-induced contractions in rabbit renal artery

Summary— The influence of vascular endothelium on angiotensin II-induced contraction and the underlying mechanisms in the rabbit renal artery were investigated. In endothelium-intact preparations, angiotensin II (3–100 nM) caused a concentration-dependent increase in tension by maximally (E_max) 0.74 ± 0.05 g. Removal of the endothelium significantly enhanced the angiotensin II-induced contractions (E_max: 3.91 ± 0.19 g). Indomethacin (10 μM) did not influence the angiotensin II-induced contractions. Methylene blue (10 μM) and N^G-methyl-1-arginine (L-NMMA, 5 μM) significantly enhanced angiotensin II-induced contractions by 418 ± 29% and 200 ± 14%, respectively, in endothelium intact preparations, but not in those devoid of endothelium. L-arginine (1 mM), but not D-arginine, reversed the L-NMMA-induced enhancement of the angiotensin II-induced contraction. The present results suggest that angiotensin II-induced contractions in rabbit renal artery are largely subject to the influence of the endothelium. The endothelium-derived relaxant factor (EDRF), rather than cyclo-oxygenase products, appears to be involved in mediating the inhibitory effects of the endothelium. Nitric oxide (NO) derived from endothelium may play a major role in inhibiting angiotensin II-induced contractions in this preparation.     

Human factors – recognising and minimising errors in our day to day practice

A significant cause of mistakes in healthcare and which are potentially harmful or fatal to patients can result from both individual clinicians and their employing organisations. The understanding and recognition of the role of human error within the healthcare setting is improving, but we still have much to learn when compared with other high‐risk organisations such as aviation where such errors can be devastating at a much larger scale. The importance of both organisational issues and human factor issues at a more personal level including tiredness, the effect of emotions and the role of situational awareness, needs to be understood by all those involved in healthcare. Potential mistakes can be reduced with simple measures which need to be recognised by, emphasised and embedded in both teams and individuals. In this review, we address the need for greater awareness of human factors, assessing the path to error and how this can be reduced to minimum levels in clinical practice.     

The platelet function defect of cardiopulmonary bypass [see comments]

The use of cardiopulmonary bypass (CPB) during cardiac surgery is associated with a hemostatic defect, the hallmark of which is a markedly prolonged bleeding time. However, the nature of the putative platelet function defect is controversial. In this study, blood was analyzed at 10 time points before, during, and after CPB. We used a whole-blood flow cytometric assay to study platelet surface glycoproteins in (1) peripheral blood, (2) peripheral blood activated in vitro by either phorbol myristate acetate, the thromboxane (TX)A2 analog U46619, or a combination of adenosine diphosphate and epinephrine, and (3) the blood emerging from a bleeding-time wound (shed blood). Activation-dependent changes were detected by monoclonal antibodies directed against the glycoprotein (GP)Ib-IX and GPIIb-IIIa complexes and P-selectin. In addition, we measured plasma glycocalicin (a proteolytic fragment of GPIb) and shed-blood TXB2 (a stable breakdown product of TXA2). In shed blood emerging from a bleeding-time wound, the usual time-dependent increase in platelet surface P-selectin was absent during CPB, but returned to normal within 2 hours. This abnormality paralleled both the CPB-induced prolongation of the bleeding time and a CPB-induced marked reduction in shed-blood TXB2 generation. In contrast, there was no loss of platelet reactivity to in vitro agonists during or after CPB. In peripheral blood, platelet surface P-selectin was negligible at every time point, demonstrating that CPB resulted in a minimal number of circulating degranulated platelets. CPB did not change the platelet surface expression of GPIb in peripheral blood, as determined by the platelet binding of a panel of monoclonal antibodies, ristocetin-induced binding of von Willebrand factor, and a lack of increase in plasma glycocalicin. CPB did not change the platelet surface expression of the GPIIb-IIIa complex in peripheral blood, as determined by the platelet binding of fibrinogen and a panel of monoclonal antibodies. In summary, CPB resulted in (1) markedly deficient platelet reactivity in response to an in vivo wound, (2) normal platelet reactivity in vitro, (3) no loss of the platelet surface GPIb-IX and GPIIb-IIIa complexes, and (4) a minimal number of circulating degranulated platelets. These data suggest that the "platelet function defect" of CPB is not a defect intrinsic to the platelet, but is an extrinsic defect such as an in vivo lack of availability of platelet agonists. The near universal use of heparin during CPB is likely to contribute substantially to this defect via its inhibition of thrombin, the preeminent platelet activator.     

Red blood cell size is important for adherence of blood platelets to artery subendothelium

The hematocrit is one of the main factors influencing platelet adherence to the vessel wall. Raising the hematocrit causes an increase of platelet accumulation of about an order of magnitude. Our studies concern the role of red cell size. We have studied this effect using an annular perfusion chamber, according to Baumgartner, with human umbilical arteries and a steady-flow system. Normal human red blood cells (MCV 95 cu mu) increased platelet adherence sevenfold, as the hematocrit increases from 0 to 0.6. Small erythrocytes from goats (MCV 25 cu mu) caused no increment in adherence in the same hematocrit range. Rabbit erythrocytes (MCV 70 cu mu) caused an intermediate increase in adherence. Red blood cells from newborns (MCV 110-130 cu mu) caused a larger increase in platelet adherence than normal red cells at hematocrit 0.4. These results were further confirmed with large red blood cells from two patients. Experiments with small red cells (MCV 70 cu mu) of patients with iron deficiency showed that platelet adherence was similar to normal red cells, provided the red cell diameter was normal. Small red blood cells of a patient with sideroblastic anemia caused decreased adherence. These data indicate that red cell size is of major importance for platelet adherence. Red cell diameter is more important than average volume. However, for size differences in the human range, the hematocrit remains the dominant parameter.     

Extended-cycle elutriation to adjust T-cell content in HLA-disparate bone marrow transplantation

We report the development of a double-cycle elutriation (DCE) technique separating 3 or greater logs of T cells from a stem-cell-enriched marrow fraction and the results of phase I T-cell depletion studies with HLA-disparate related bone marrow transplantation (BMT) donors in two patient groups. In group 1, 10 patients with refractory hematopoietic malignancies received combination chemotherapy, total body irradiation (TBI), and immunosuppression (pre- and post-BMT), and hematopoietic rescue with a marrow transplant, depleted of T cells by elutriation. Potentially to promote engraftment and a graft-versus- leukemia (GVL) effect, 0.5 to 0.75 x 10(5) T cells/kg were added back. All 10 patients engrafted. Five patients developed acute graft-versus- host disease (GVHD; four grade II, one grade III) and two subsequently developed chronic GVHD. Two patients have relapsed (median follow-up, 206 days; range, 46 to 1,035). Four patients died of BMT-related complications (three of infection, one of veno-occlusive disease [VOD]). Four patient are disease-free survivors (median follow-up, 960 days; range, 670 to 1,035). Group 2 included five infants, four with congenital lymphohematopoietic deficiencies and one with refractory acute lymphocytic leukemia (ALL). In these infants, busulfan and increased cyclophosphamide were substituted for TBI. Only the ALL patient received added T cells. Three patients engrafted: one has stable mixed chimerism, one relapsed with ALL, and one rejected the marrow. One patient had primary autologous recovery, while another failed to engraft. None developed GVHD. We conclude that, in this setting of HLA-disparate BMT with post-BMT antithymocyte globulin (ATG) and corticosteroids, DCE significantly depletes T cells from the marrow and that a defined number of T cells can be added without the occurrence of severe GVHD.     

Inhibition of bone marrow myeloid precursor cell proliferation by chemotactic oligopeptides

Three N-formylated oligopeptides with different known activities as chemotactic factors for leukocytes were studied to determined if these mediators affect the in vitro proliferation of myelomonocytic colony- forming cells (CFU-C) recovered from murine bone marrow. All three oligopeptides inhibited CFU-C growth in a dose-dependent fashion that correlated with their relative potencies as chemotactic factors. This inhibition was not altered by growth of CFU-C in the presence of indomethacin, by varying the concentrations of colony-stimulating factor (CSF), or by depleting marrow cell preparations of mature granulocytic elements. These studies indicate that chemotactic factors may mediate myelosuppression through effects on committed myeloid precursor cells in the marrow.     

Type I Glanzmann thrombasthenia patients from the Iraqi-Jewish and Arab populations in Israel can be differentiated by platelet glycoprotein IIIa immunoblot analysis

A sensitive immunoblot technique for platelet glycoprotein IIIa (GPIIIa) was used to analyze the platelets of patients living in Israel who meet the diagnostic criteria for type I Glanzmann thrombasthenia. When reacted with solubilized normal platelets, a rabbit antiserum to GPIIIa identified a major band at molecular weight (mol wt) 90,000 and three additional minor bands at Mr 110,000, 81,000, and 64,000. The major band could not be detected, and the minor bands were either markedly reduced or absent in the platelet samples from 14 of the 15 patients from the Iraqi-Jewish population. In contrast, in all four Arab patients tested, the major band was detectable, although at markedly reduced levels, and the minor bands were either markedly reduced or absent; an additional minor band at mol wt 47,000 was also present in the platelets from these patients. One Iraqi-Jewish patient had a unique pattern in which two of the bands were present but reduced and two were undetectable. We conclude that the protein defect, and thus presumably the genetic defect, causing Glanzmann thrombasthenia in the majority of patients in the Iraqi-Jewish population differs from that in the Arab population, and we confirm that there is considerable biochemical heterogeneity among the patients who meet the criteria for type I Glanzmann thrombasthenia.