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Biomedical subjects

G Rock

Publications and source records attributed to G Rock.

At least 19 recordsLinked to original sources
PubMed1992

Thrombotic thrombocytopenic purpura: outcome in 24 patients with renal impairment treated with plasma exchange. Canadian Apheresis Study Group.

The Canadian Apheresis Study Group recently completed a randomized clinical trial involving 102 patients with thrombotic thrombocytopenic purpura (TTP), in which treatment with plasma infusion and treatment with plasma exchange were compared. Thirty-three other patients were ineligible or refused to be randomly assigned in the trial. Of the 33 patients, 24 were assessed as ineligible because they would be unable to tolerate the fluid input that would occur if they were randomly assigned to receive plasma infusion. All 24 patients had oliguria and elevated creatinine and/or blood urea nitrogen level. These 24 patients were treated with acetylsalicyclic acid, dipyridamole, and plasma exchange according to the standardized protocol defined in the trial. Blood for tests of factors possibly involved in the pathogenesis of TTP was drawn before exchange and at intervals during and after exchange. The mean platelet count before exchange was 35.5 x 10(9) per L. In 12 of the 24 patients, the platelet count reached 150 x 10(9) per L or greater by 7 days after the initiation of plasma exchange. Three patients responded partially, in that their platelet count increased to at least twice that at presentation, but remained below 150 x 10(9) per L. One patient died during the first week. Of the eight other patients who experienced treatment failure at the 7-day assessment point, six subsequently responded, four while continuing to receive plasma exchange and two after plasma exchange had been discontinued. Of the 15 patients who either responded fully or responded partially by the end of the first cycle, all survived.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗
PubMed1992

Repeat plateletpheresis: the effects on the donor and the yield.

Requirements for HLA ot otherwise matched single-donor platelets may sometimes require repeat plateletpheresis of an individual donor. AABB standards permit the repeat collection of platelets by plateletpheresis of a single donor at 48-hour intervals, whereas recent recommendations from England state that a donor should not donate platelets more often than 12 times a year. To assess the effects of repeat plateletpheresis on the donor, we have studied the hematological indices and the product yields following every other day plateletpheresis of 13 normal donors who gave a total of 10 times during 22 days. The platelet count decreased in every case, with the lowest values reached at the third donation (day 5). The pre-donation count averaged 225 +/- 53 x 10(9)/l decreasing to 174 +/- 27 x 10(9)/l at the time of the 3rd donation then increasing by the 6th donation to 198 +/- 46 x 10(9)/l. The yield in the product decreased from 3.2 +/- 1.3 x 10(11) on day 1 to 2.6 +/- 0.8 x 10(11) for the third donation, returning thereafter to higher values. In spite of the expected and apparent stimulation of platelet production through feedback, the counts did not rebound above starting levels indicating a basic homeostatic mechanism. The donor WBC showed minimal changes during the study period, however there was a significant increase in the total number of lymphocytes by the 3rd procedure; this was corrected by the fifth procedure. The absolute number and ratio of T4 (helper) and T8 (suppressor) lymphocytes did not change.(ABSTRACT TRUNCATED AT 250 WORDS)

Blood Donors↗
PubMed1992

Target antigens of anti-platelet antibodies in patients with steroid-resistant ITP of recent onset. Canadian Apheresis Study Group.

Recent application of Western blotting procedures in the detection of anti-platelet antibodies has permitted more refined definition of reactivity. We report on the results of anti-platelet antibody assays in a series of 19 patients with recently diagnosed (less than 6 months duration) steroid-resistant, idiopathic thrombocytopenia purpura (ITP). At presentation, six of the 19 patients had a positive test for platelet-associated IgG (PAIgG) as measured by the direct radial-immunodiffusion (RID) assay, whereas three of the 19 were positive with the direct-platelet-suspension-immunofluorescence test (DPSIFT). The indirect-platelet-suspension-immunofluorescence test (IPSIFT) demonstrated antibodies in seven of the sera. Following Western blot (WB) analysis, the serum of 7/19 patients (only three of which were positive in the IPSIFT) could be shown to react with platelet antigens. Two patterns were seen: in four cases there were bands of apparent molecular weights of 60,000, 55,000 and 50,000; in the other three samples, a single band near 90,000 was demonstrated. Unlike the situation reported for chronic ITP, no reactivity was seen against higher molecular weight antigens other than the 'non-specific' binding at apparent molecular weight 200,000 which is also seen with normal sera. The data suggest that antibodies reacting against specific platelet antigens are present in the serum of some patients with recent onset ITP.

Adult↗
PubMed1991

Storage of platelets in balanced salt solutions: a simple platelet storage medium.

When a commercially available intravenous solution, plasmalyte-A, was added to platelet pellets as a platelet storage medium (PSM) after more than 85 percent of the plasma had been expressed, the platelets functioned equally well, after 5 days of storage, in platelet aggregation, release reaction, and serotonin uptake as did platelets stored in plasma. The level of fibrinopeptide A was significantly different in the PSM. Similarly, lower levels of kallikrein and complement components in the PSM-stored platelets indicated reduced activation of plasma enzyme systems. Morphology scores showed better shape maintenance in PSM, with values of 255 versus values of 185 in plasma (time zero, 280); electron microscopy also showed somewhat better structural maintenance in PSM. Glucose consumption, lactate and ammonia production, and fatty acid oxidation were also reduced in PSM. No significant differences in pH, white cell count, pO2, pCO2, or lactic dehydrogenase were observed after 5 days of storage in plasma or PSM; however, platelet counts were reduced after 5 days in plasma but remained constant in PSM. The beta-thromboglobulin release was significantly lower in the PSM-stored platelets after 5 days. The volume of platelet membrane glycoprotein lb (which is responsible for platelet adhesion) decreased 15 percent in plasma following storage, whereas a decrease of only 5 percent was noted in PSM. There was less leaching of plasticizers in PSM than in plasma. Survival and recovery using 51Cr-labeled autologous platelets showed that, after 5 days of storage, the recovery of PSM-stored platelets was 63 percent and the survival was 7.7 +/- 0.8 days (multiple hit model).(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed1990

Development of a heat-treated factor VIII/von Willebrand factor concentrate prepared from heparinized plasma.

A high yield, intermediate purity factor VIII concentrate derived from heparinized plasma has been developed which can be heat-treated at 60 degrees C, 68 degrees C or 80 degrees C/72 h to permit inactivation of viral contaminants which may be present. After cold reprecipitation of the heparinized cryoprecipitate (CRC), the resolubilized CRC precipitate was adjusted to 25-30 mg/ml protein and pH 6.35 +/- 0.1 and incubated for 1 h at 8 degrees C. After centrifugation to remove the precipitated fibrinogen and fibronectin, a factor VIII-rich supernatant can be recovered which contains greater than 500 units of VIII:C per liter of starting plasma (Method I product) at a purity of 1.5 U/mg protein. Adjusted to 50 mM glycine and pH 6.8, the product can be lyophilized and heat-treated at 60 degrees C/72 h without a significant loss of VIII:C activity. However, at 68 degrees C or 80 degrees C/72 h, temperatures now reported to be more effective in viral inactivation, the recoveries were reduced to 68 and 33% respectively. Significantly improved recoveries after heat-treatment (HT) at 68 degrees C or 80 degrees C/72 h were achieved if the 8 degrees C supernatant product was prepared by a modified procedure (Method II). This further reduces the fibrinogen content of the product while maintaining VIII:C yields greater than 500 U/l at a purity of 1.9 U/mg. When adjusted to 50 mM glycine and 1-2% (w/v) sucrose (pH 6.8), lyophilized and heat treated at 60 degrees C, 68 degrees C or 80 degrees C/72 h, the VIII:C recoveries of Method II product were 88-100%, 79-84% and 80-83% of pre-HT levels respectively. The yield of VIII:C was greater than 400 U/l at a purity of 1.6-1.4 U/mg at 1-2% (w/v) sucrose even after the severe heat-treatment at 80 degrees C. In addition, the von Willebrand factor multimers are similar in size and triplet pattern to those observed in routine cryoprecipitate preparations.

Chemical Precipitation↗
PubMed1990

DDAVP-induced release of von Willebrand factor from endothelial cells in vitro: the effect of plasma and blood cells.

The vasopressin analogue 1-deamino-8-D-arginine vasopressin (DDAVP) causes an immediate, transient rise in plasma levels of von Willebrand factor (vWF) after its administration. Although it is recognized that vascular endothelial cells play an essential role in this process, the molecular basis of the response is not understood. We have investigated the phenomenon using human umbilical vein endothelial cells as an in vitro model. When normal individuals were stimulated with DDAVP, plasma from blood samples collected subsequently caused the release of vWF from cultured endothelial cells over a 24 h period (22-46% increase over baseline), compared to control plasma (5-17%). DDAVP added directly to the endothelial cells produced no increase in vWF release. When whole blood was treated in vitro with DDAVP, and the plasma subsequently added to endothelial cells, a significant increase in vWF secretion was found. Peripheral blood mononuclear cells were then tested. In the presence of DDAVP, an increased response occurred. Further fractionation of these cells showed that monocytes were largely responsible, causing an increased vWF release of 162% at 2 h. These observations were reinforced by finding that the supernatants of monocytes incubated with DDAVP were also effective in causing increased vWF release (118% compared to 58% for the control sample). Our studies suggest that DDAVP plays an indirect role in causing the release of vWF from endothelial cells, and that peripheral blood monocytes may act as intermediary target cells, which then produce factor(s) acting directly on endothelial cells.

Cells, Cultured↗
PubMed1990

A comparison of results obtained by two different chromium-51 methods of determining platelet survival and recovery.

A number of different methods exist that use chromium-51 to determine platelet survival and recovery. A 1986 article in TRANSFUSION described the recommended methods for conducting such studies in the hope of standardizing methodology and permitting interlaboratory comparison of results. The results obtained with the recommended method have been compared with those of our previous method. With the new method, recovery of fresh random-donor platelets prepared in polyolefin bags was 76 +/- 6 percent with a survival of 9.3 +/- 2.8 days (n = 4). After 5 days of storage, these values were 67 +/- 8 percent and 7.8 +/- 1.9 days. Similar values were obtained for fresh and stored platelets collected on automated cell separators. However, when our previous (pre-1986) method of evaluation was used, recovery of fresh platelets in the polyolefin bags was 56 +/- 11 percent, and survival was 8.6 +/- 1.3 days. The 5-day values were 36 +/- 5 percent and 6.9 +/- 2.7 days. These values are significantly lower (p less than 0.05) than those obtained with the newer method, but they are in agreement with those previously reported for other techniques. Thus, the new method consistently gives higher values, possibly as a result of a less harmful labeling procedure.

Blood Platelets↗