Fibrinolytic and haemostatic responses to desamino-D-arginine vasopressin (DDAVP) administered by intravenous and subcutaneous routes in healthy subjects.

DDAVP was administered at 0.4 microgram kg-1 intravenous (i.v.) and subcutaneous (s.c.) routes to 6 healthy subjects in a double blind crossover study. Both study treatments were well tolerated. Flushing occurred after both treatments but was more prominent after i.v. than after s.c. DDAVP. Mild transient local discomfort at the s.c. injection site occurred in 5 of 6 subjects. The mean peak factor VIII (FVIII) response was 369% and 247% of baseline after i.v. and s.c. DDAVP respectively and the maximum increase in FVIII occurred earlier with the i.v. route. Changes in FVIII antigen (FVIII:Ag) and von Willebrand factor antigen (vWF:Ag) were also monitored. Tissue-type plasminogen activator (t-PA) activity measured by a chromogenic assay employing soluble fibrin had a median peak value of 2.9 IU ml-1 at 20 min after i.v. and of 1.9 IU ml-1 at 60 min after s.c. DDAVP. t-PA antigen was also measured so that the specific activity of circulating t-PA could be determined. Preinjection median values of 14,650 and 13,700 IU mg-1 increased to peak median values of 236,200 IU mg-1 at 20 min after i.v. and 202,400 IU mg-1 at 60 min after s.c. DDAVP. Plasminogen activator inhibitor (PAI) activity fell following DDAVP and became undetectable in some subjects during the sampling period. The ratio of maximum fibrinolytic response was similar to the ratio of maximum haemostatic responses obtained by two routes of injection. Our results indicate that s.c. DDAVP might successfully replace i.v. DDAVP in several applications such as confirmation of haemostatic or fibrinolytic responsiveness in patient groups; for obtaining FVIII enriched plasma; as well as its obvious potential usefulness in home treatment of haemophilia A and von Willebrand's disease.

Incidence and clinical significance of protein-bound vitamin B12 malabsorption.

Patient records from January 1975 to December 1984 were analysed to assess the possible incidence of protein-bound vitamin B12 malabsorption. This condition is characterised by a low serum vitamin B12 level and a normal Schilling test but impaired absorption of vitamin B12 bound to protein. We found that 48 (25%) patients with a low serum cobalamin level unexplained by other causes had a normal Schilling test. Megaloblastic haemopoiesis was found in 25 of these. From this group, all 10 patients who had a test of protein-bound vitamin B12 absorption showed impaired absorption. Protein-bound vitamin B12 malabsorption may represent an early phase of pernicious anaemia when hypochlorhydria precedes intrinsic factor deficiency and should be tested for when the serum vitamin B12 level is decreased and the Schilling test is normal.

Monoclonal antibody analysis of canine hemopoietic cells. Role of Ia-like and Thy-1 antigens in bone marrow engraftment.

The expression of Ia-like (class II MHC) antigens on canine hemopoietic cells was investigated using a cytotoxic murine monoclonal antibody, WM-2, reactive with dog Ia-like antigens. Another monoclonal antibody, WMD-1, reactive with canine Thy-1 antigen, was used as a positive control. Depletion of Ia+ cells from dog bone marrow by complement-mediated lysis with WM-2 antibody failed to inhibit growth of granulocyte-macrophage progenitors (CFUGM) in vitro, while WMD-1 produced complete inhibition of CFUGM. Lethally irradiated dogs receiving bone marrow autografts depleted of Ia-positive cells ex vivo showed initial engraftment, followed by prolonged pancytopenia, and eventual complete recovery of marrow function in the majority of animals. In contrast, dogs receiving autografts treated with WMD-1 and complement all died of marrow failure. We interpret these results as indicating: (1) that Thy-1 antigen is present on hemopoietic stem cells essential for marrow engraftment; and (2) that the expression of Ia antigens on hemopoietic cells is heterogeneous and related to the level of stem cell maturation. While Ia appears to be present on a stem cell population at an earlier stage than CFUGM, as evidenced by the transient phase of graft failure seen in dogs receiving Ia-depleted marrow, the most primitive stem cell, responsible for long-term engraftment, is effectively Ia-negative.

Acute leukemia characterized by trisomy 8 in Down's syndrome.

Of the myeloproliferative disorders which develop in Down's syndrome, acute leukemia associated with trisomy 8 has distinct characteristics. It is non-lymphoblastic in type and has a preleukemia phase in which thrombocytopenia is a prominent feature. One case occurring in a 20 mth-old girl is reported and 3 other similar cases reviewed. Acquired trisomy 8 in Down's syndrome is linked to leukemogenesis and confers non-lymphoblastic differentiation.