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Plasma Antithrombin III (ATIII) activity was quantitated in 24 clinically normal Standardbred/Thoroughbred horses using a clotting time technique. ATIII activity ranged from 80 to 106% of the pooled reference standard plasma, with a mean of 94%. Horses presenting with impaction or spasmotic colic (n=17) had normal plasma ATIII activity, while 15 horses presenting with acute diarrhea/colitis had significantly lower plasma ATIII activity with a mean of only 74% of the reference plasma. Seven horses presenting with liver disease had significantly higher plasma ATIII activity with a range of 127 to 177% of the pooled reference plasma. Fifty-seven equine plasmas were retested using a rapid chromogenic substrate technique for quantitating plasma ATIII activity. A good correlation (r =+0.83) existed between clotting time and chromogenic determinations of ATIII. Pooled normal canine, human and bovine plasmas had only 65, 62 and 79%, respectively, of the ATIII activity of the equine reference plasma.

Steroid hormone receptors were studied in 42 patients with primary, recurrent or metastatic breast cancer in cryostat frozen section and imprint preparations. The ligands, 17 B-estradiol-6-carboxymethyloxine-bovine serum album fluorescein isothiocyanate (FITC-BSA estradiol) and hydroxyprogesterone-hemisuccinate bovine serum album tetramethylrhodamine isothiocyanate (TMRITC-BSA progesterone) were used in the fluorescent cytochemical method. Results were compared with standard dextran-coated charcoal (DCC) biochemical assay. Overall, significant correlation between biochemical values and cytochemical fluorescence results was found. However, the imprint results were more sensitive and more specific than the frozen section results. A statistically significant difference (P less than 0.05) was observed between touch preparation material and frozen section specimens by the fluorescent method.

The aims of this paper are to demonstrate the stainability of estrogen, CEA, and ferritin in breast carcinomas, fibroadenomas, and fibrocystic diseases; to examine whether the findings of endogenous estrogen using the immunohistochemical detection method are related to estrogen receptor (ER) assays; and to determine whether the stainability of estrogen, CEA, and ferritin were related to the prognosis of breast carcinomas. In breast cancer, the stainability of estrogen using the peroxidase-antiperoxidase (PAP) method was positively correlated with the dextran-coated charcoal (DCC) assay for ER. In breast cancers, the percentage of positive staining was 46% for estrogen, 48% for CEA, and 47% for ferritin. With all three stains, significant differences were observed between cancer and benign diseases. Cases that were both positive for estrogen staining and negative for CEA showed a good prognosis after the recurrence of disease. Our data suggest that the immunohistochemical staining of estrogen, CEA, and ferritin might predict the biological behavior of breast carcinomas and be a prognostically useful indicator of breast cancer patients.

1. Natural proteinase inhibitors are divided into polysaccharides, plasma proteinase inhibitors and natural non-plasma inhibitors. 2. Polysaccharides are antithrombin-III and heparin co-factor-II dependent or independent regarding their biological activity. Knowledge of the inhibitory mechanism at a molecular level was gained by the study of heparin. 3. Antithrombin-III, heparin-co-factor-II and alpha 2-macroglobulin are the most important plasma proteinase inhibitors involved in coagulation. alpha 2-macroglobulin has a particular inhibitory mechanism. 4. Non-plasma proteinase inhibitors were isolated from many species. They inhibit mainly the contact activation and fibrinolysis. 5. The evolutionary relationships are poorly understood.

The presently recognized correlations between various clinical parameters and the concentrations of estrogen and progesterone receptors in breast cancer biopsies are largely based on receptor values obtained using the dextran-coated charcoal (DCC) method. This assay method is highly sensitive to slight changes in assay protocol, and differences in assay methodology may account for the wide variation in proportions of receptor positive patients reported by different centers. A survey of various aspects of the assay method that may lead to reproducible, systematic differences in concentrations of receptor levels is presented; and methods of compensating for or correcting these potential differences are discussed. The following aspects are considered: a) constitution of biopsy tissue, b) method of tissue homogenization, c) absorption of ligands to surfaces, d) inclusion of molybdate in the assay buffer, e) composition of the DCC slurry, and f) handling of samples for liquid scintillation counting. Differences in methods used to homogenize tissue in Europe and the U.S.A. may account for differences observed in the correlation of DCC assay results obtained using the recently-introduced monoclonal ER-EIA technique.

A continuous line of human breast carcinoma cells, VHB-1, was established in culture following collagenase treatment of an infiltrating duct cell carcinoma. The cells displayed an epithelial pattern and multiplied rapidly. Maintained in monolayer culture, the VHB-1 cells exhibited a 30-h doubling time and a plating efficiency of 20%. The cells possessed an abnormal karyotype with a mode of 70-74 chromosomes per cell. The karyotype was heavily rearranged and numerous marker chromosomes were found. Transplantation of the cells into nude mice produced tumors bearing histological resemblance to the original material. The VHB-1 cells contained significant levels of prolactin receptors, were steroid hormone (estrogen, progesterone, androgen, glucocorticoid) receptor positive, and were capable of functional differentiation in vitro. These characteristics make the VHB-1 cell line a suitable model for studying the biological properties of human breast tumors.

The need to fully heparinize patients undergoing extracorporeal therapy often leads to hemorrhagic complications. Two approaches have been used to solve this problem. The first involves full heparinization of blood entering the extracorporeal device followed by the elimination of heparin from the blood returned to the patient using an immobilized heparinase reactor system. Animal studies have demonstrated the successful elimination of heparin's anticoagulant activity using this reactor. The second approach uses very low molecular weight (VLMW) heparins with improved properties. Although low molecular weight heparins and heparinoids have been successfully used in hemodialysis, these preparations are polydisperse mixtures. New VLMW heparins are described which are pure, monodisperse, structurally defined drugs and show improved pharmacokinetics and greater specificity than heparin. The separation of ATIII and HCII mediated activity against factors IIa and Xa may permit extracorporeal therapy with only partial anticoagulation resulting in increased antithrombotic activity with decreased hemorrhagic side-effects. Finally, these VLMW heparins suggest certain desirable structural characteristics in the design blood compatible non-thrombotic synthetic polymers for use in extracorporeal devices.

Rats fed a carbonyl iron-supplemented diet for 4-15 months were studied for iron content and morphologic changes in the liver, spleen, intestinal mucosa, pancreas and heart. All organs had an increased iron content measured by atomic absorption, with the highest concentrations in the liver and spleen. The periportal distribution of stored iron in the liver was similar to that in human hemochromatosis. In animals treated beyond 6 months Kupffer cells and sinusoidal lining cells also showed cytosiderosis. Electron microscopy provided information on ferritin and hemosiderin content and distribution within parenchymal and sinusoidal cells of the liver but no excessive fibrosis was found. Except for the spleen, the other organs showed less iron deposition. Iron-filled lysosomes (siderosomes) were found in macrophages in the intestinal lamina propria and pancreas, as well as in enterocytes, pancreatic acinar cells and heart muscle cells. Heavily iron-laden siderosomes had increased membrane instability which was demonstrated both morphologically and by measurements of latent lysosomal enzyme activities. Even though cirrhosis was not found, the distribution pattern of accumulated storage iron and lysosomal lability indicated that the carbonyl iron-fed rat is a suitable experimental model for human hemochromatosis.

Thrombin generation, as evidenced by plasma fibrinopeptide A (FPA) concentrations, was studied during blood collection from donors taking oral contraceptives (OC). 450 ml blood were drawn into Fenwal PVC bags from 26 OC users and 28 nonusers. Blood samples for determination of FPA, beta-thromboglobulin (BTG), thrombotest (TT), prekallikrein (PKK), antithrombin-III (AT-III) and factor VIII procoagulant activity (FVIII:C) were drawn from the bags immediately after ending blood donation and following storage for 24 h at 4 degrees C. The FPA concentrations following donation were significantly higher in the OC than in the control group (p less than 0.05). The levels of PKK were also higher in blood obtained from OC users (p less than 0.001), as was the FVIII:C level, the latter difference, however, was not significant (p = 0.06). No cold-promoted activation of factor VII, as evidenced from TT, was detected following storage at 4 degrees C, neither was any change observed in the FPA, PKK and AT-III levels. The BTG concentrations increased significantly during storage, most pronounced in the control group (p less than 0.05). The decay of FVIII:C was similar in the two groups, averaging 24.7%. No correlation was observed between the FPA levels and the other parameters determined. We conclude that thrombin generation is more pronounced during routine blood collection from donors taking OC.

The sensitivity to medroxyprogesterone acetate (MPA) and tamoxifen (T) and their combination was assayed in 13 patients with untreated endometrial cancer by an in vitro ATP-bioluminescence method. The method measures the levels of adenosinetriphosphate (ATP), the basic energy source of living cells. A tumor was considered to respond to the drug, if the proportion of living cells after manipulation was 50% or less from unmanipulated control culture. Estrogen (ER) and progesterone (PR) receptors were assayed by the DCC-method and the results calculated by Scatchard-analysis. ER (greater than or equal to 3 fmol/kg cytosol protein) was present in all tumors and PR (greater than or equal to 10 fmol/kg cytosol protein) in 85% of the tumors. The response rate in vitro to MPA was 67% (8 out of 12 tumors), to T 18% (2 out of 11) and to their combination 69% (9 out of 13). The G1 tumors responded statistically significantly better to MPA (p less than 0.01) and MPA + T (p less than 0.02) as compared to T. MPA produced higher cell kill of G1 than G2 tumors (p less than 0.05). The ER content correlated with the effect of MPA in vitro in 67%, with the effect of T in 18% and with that of their combination in 69% of the tumors. The PR content correlated with the effects of MPA in vitro in 83%, with the effect of T in 36% and with that of their combination in 54% of the tumors. It was concluded that the in vitro ATP-bioluminescence method provides valuable information besides steroid receptor determinations for sensitivity testing of endometrial cancer to hormones.

Insulin and two closely related peptides, insulinlike growth factors I and II (IGF-I and IGF-II), as well as their respective receptors, overlap in structure, specificity, and function. Very little is known about the role of these peptides and their receptors in embryogenesis. We have found that chick embryo tissues express both insulin and IGF receptors at very early stages of organogenesis. Each type of receptor is regulated throughout embryogenesis in a manner that is tissue-specific. Substances with insulin immunoactivity and bioactivity are detected in chick embryos at prepancreatic stages (days 2 and 3). Embryos that grow in the presence of antiinsulin antibodies (which are known to neutralize the bioactivity of insulin but not that of the IGFs found in adult vertebrates) demonstrate retarded growth and impaired differentiation. These data support the hypothesis that insulin or insulin-related peptides are essential elements for normal development in the chick embryo.

Human plasma contains two distinct heparin dependent thrombin inhibitors; antithrombin III (ATIII) and Heparin cofactor II (HCII). The latter is also known as antithrombin BM, because of its moderate binding affinity to heparin. The protein is distinct from ATIII by immunological and functional criteria as well as by its amino acid sequence. HCII selectively inhibits thrombin by forming a 1:1 molar complex with the protease and has no activity towards other coagulation serine proteases. Dermatan sulphate, a glycosaminoglycan, specifically activates HCII and increases its thrombin neutralizing activity by over a thousand fold. Dermatan sulphate does not catalyze the activity of ATIII. Human fibroblasts have been shown to accelerate the neutralization of thrombin by HCII. These cells can synthesize proteoglycans containing dermatan sulphate. Current evidence would thus suggest that extravascular tissues are the major sites of action of HCII. The specificity of dermatan sulphate for HCII has allowed the development of functional assays for this protein. Reduced levels have been observed in patients with significant hepatocellular dysfunction and in association with disseminated intravascular coagulation. Two families have been reported with hereditary HCII deficiency and recurrent thrombosis (both venous and arterial). Although these observations suggest a role for HCII in the modulation of hemostatic system, further studies are required to define the importance of HCII deficiency as a marker of thrombosis.

Oestrogen receptor (ER) analysis of breast cancers by the standard dextran coated charcoal (DCC) method and the oestrogen receptor immunocytochemical assay (ERICA), shows that ERICA is more sensitive. We find that the immunogold-silver staining technique (IGSS), which is used on paraffin sections, is applicable to the ERICA antibody and that the DCC and IGSS methods have comparable sensitivity. Reasons for wishing to develop an improved method for oestrogen receptor localisation in paraffin sections and its advantages are given.

Determinations of coagulation/fibrinolysis parameters thrombin-antithrombin III complex (TAT) and D-dimers (cross-linked fibrin degradation product) were carried out in order to prove that preeclampsia is a chronic disseminated intravascular coagulation (DIC) state. Besides the parameters TAT and D-dimers, antithrombin III (ATIII), fibrin degradation products and platelets were measured as well. Even in normal pregnancy there is an activation of coagulation, reflected in a hypercoagulative state that is proceeding down to the formation of thrombin. This thrombin is, however, nearly completely inactivated by ATIII, so that no fibrin is formed. This inactivation is solely reflected by the increase of TAT in the blood. In preeclampsia, however, where no such rapid changes as in acute DIC occur, the increase of TAT is accompanied by a decrease of ATIII and platelet counts and an increase of D-dimers; this demonstrates much more clearly the chronic DIC nature of preeclampsia than the results from studies carried out so far.

The Monoclonal Antibody technology has been used in 29 cases of ovarian cancer. The immuno-enzyme-assay detected positive levels of estrogen cytoplasmatic receptor in 51.8% of the cases as well as in the nuclear (51.8%). Moreover, the ER/EIA technique screened positive levels of Total ER (ER/t) in 72.4% versus 65.5% obtained by DCC-method. 24.1% of the cases had negative ER/t levels observed by EIA. The monoclonal antibody anti-ER is a very interesting method for studying hormone-dependent tissue, because it uses an immunological binding to antigenic protein (receptor).

The relationship between increased risk in relatives over population prevalence (lambda R = KR/K) and probability of sharing zero marker alleles identical by descent (ibd) at a linked locus (such as HLA) by an affected relative pair is examined. For a model assuming a single disease-susceptibility locus or group of loci tightly linked to a marker locus, the relationship is remarkably simple and general. Namely, if phi R is the prior probability for the relative pair to share zero marker alleles identical by descent, then P (sharing 0 markers/both relatives are affected) is just phi R/lambda R. Alternatively, lambda AR, the increased risk over population prevalence to a relative R due to a disease locus tightly linked to marker locus A, equals the prior probability that the relative pair share zero A alleles ibd divided by the posterior probability that they share zero alleles ibd, given that they are both affected. For example, for affected sib pairs, P (sharing 0 markers/both sibs are affected) = .25/lambda S. This formula holds true for any number of alleles at the disease locus and for their frequencies, penetrances, and population prevalence. Similar formulas are derived for sharing one and two markers. Application of these formulas to several well-studied HLA-associated diseases yields the following results: For multiple sclerosis, insulin-dependent diabetes mellitus, and coeliac disease, a single-locus model of disease susceptibility is rejected, implying the existence of additional unlinked familial determinants. For all three diseases, the effect of the HLA-linked locus on familiality is minor: for multiple sclerosis, it accounts for only a 2.5-fold increased risk to sibs over the population prevalence, compared to an observed value of 20; for coeliac disease, it accounts for approximately a 5.25-fold increased risk to sibs, while the observed value is on the order of 60; for insulin-dependent diabetes mellitus, it accounts for a 3.42-fold increased risk in sibs, while the observed value is 15. In all cases, the secondary determinants must be outside the HLA region. For tuberculoid leprosy, an unlinked familial determinant is also implicated (increased risk to sibs due to HLA = 1.49; observed value = 2.38). For hemochromatosis and Hodgkin's disease, there is little evidence for HLA-unlinked familial determinants. With this formula, it is also possible to examine the hypothesis of pleiotropy versus linkage dis-equilibrium by comparing lambda AS with the increased risk to sibs due to the associated allele(s).(ABSTRACT TRUNCATED AT 400 WORDS)

Propylthiouracil and methimazole are frequently used in the management of hyperthyroidism. Two patients in whom adverse immunologic effects other than isolated agranulocytosis developed during treatment with propylthiouracil are described. A review of the literature revealed 53 similar cases over a 35-year period. Rash, fever, arthralgias and granulocytopenia were the most common manifestations. Vasculitis, particularly with cutaneous manifestations, occurs and may be fatal. The clinical evidence suggests that an immunologic mechanism is involved. A number of different autoantibodies were reported, but antinuclear antibodies were infrequent, and none of the cases met the criteria for a diagnosis of systemic lupus erythematosus. Thus, the reactions do not represent a true drug-induced lupus syndrome. Current hypotheses and experimental data regarding the cause of the reactions are reviewed. No specific clinical subgroup at high risk can be identified, and manifestations may occur at any dosage and at any time during therapy. Cross-reactivity between the two antithyroid drugs can be expected. Except for minor symptoms (e.g., mild arthralgias or transient rash), such reactions are an indication for withdrawal of the drug and the use of alternative methods to control the hyperthyroidism. In rare cases of severe vasculitis a short course of high-dose glucocorticoid therapy may be helpful.

Gram-negative septic shock remains a major clinical problem. One frequently encountered complication of sepsis is disseminated intravascular coagulation (DIC). The present study was to determine in an Escherichia coli endotoxemia awake rat model the efficacy of antithrombin-III (AT-III) prophylaxis and to explore the role of DIC in the pathogenesis of endotoxemia. We demonstrated that DIC occurs very early, before the appearance of detectable serious abnormalities in cardiovascular, metabolic, and biochemical variables indicative of organ damage or dysfunction; AT-III prophylaxis significantly ameliorates DIC, as evidenced by completely preventing the fall in plasma fibrinogen concentration and significantly limiting the increases in prothrombin time and activated partial thromboplastin time after 4 hours of endotoxemia; and AT-III prophylaxis dramatically increases permanent survival. Results of this study suggest that AT-III prophylaxis is very protective above a threshold dosage in an endotoxemic rat model and that protection is in part due to ameliorating DIC. Our data also suggest that DIC occurs very early during endotoxemia and may in part be responsible for the pathogenesis of endotoxemia in the rat. We conclude that AT-III prophylaxis may be efficacious in conditions of impending DIC, such as gram-negative septicemia/endotoxemia.

The evolution of serum ferritin levels in 111 chronic-hemodialysis patients is prospectively studied. Patients were classified in two groups according to the presence or absence of 'hemochromatosis antigens' (HLA A3, B7 or B14) in their HLA typing. Levels of serum ferritin were similar in both groups before they started dialysis and during the first year. On the contrary, in the second and third hemodialysis years serum ferritin was higher in the group carrying 'hemochromatosis antigens'. These differences were observed in patients treated with parenteral iron either in the form of transfusions or as intravenous dextran-iron but not in patients receiving oral iron. We conclude that the risk of developing iron overload is greater in hemodialysis patients with HLA A3, B7 or B14. Nevertheless, this potential risk can be minimized with a restrictive policy on the use of parenteral iron (transfusions, intravenous dextran-iron).

In the present study, we have evaluated the relationship between serum ferritin (SF) levels, 'hemochromatosis allele(s)', blood transfusions and iron parenteral administration in 69 hemodialysis patients. We demonstrated significantly higher SF levels in patients with hemochromatosis allele(s) (HA+) than in patients without hemochromatosis alleles (HA-). In addition, HA+ patients who had received blood transfusions up to 15 months prior to the study had SF levels even higher than those without blood transfusions. On the other hand, HA- patients had normal levels of SF, independent of blood transfusions. After intravenous administration of 1 g iron saccharate, SF levels were significantly higher only in HA+ transfused patients. In conclusion, our study demonstrated that HA+ patients are at a higher risk of iron overload and therefore the use of transfusional and/or parenteral iron should be strictly limited.

An EcoRI chromatin fragment containing the adult beta-globin gene and flanking sequences, isolated from chicken erythrocyte nuclei, sediments at a reduced rate relative to bulk chromatin fragments of the same size. We show that the specific retardation cannot be reversed by adding extra linker histones to native chromatin. When the chromatin fragments are unfolded either by removing linker histones or lowering the ionic strength, the difference between globin and bulk chromatin fragments is no longer seen. The refolded chromatin obtained by restoring the linker histones to the depleted chromatin, however, exhibits the original sedimentation difference. This difference is therefore due to a special property of the histone octamers on the active gene that determines the extent of its folding into higher-order structure. That it is not due to the differential binding of linker histones in vitro is shown by measurements of the protein to DNA ratios using CsCl density-gradients. Both before and after selective removal of the linker histones, the globin gene fragment and bulk chromatin fragments exhibit only a marginal difference in buoyant density. In addition, we show that cleavage of the EcoRI fragment by digestion at the 5' and 3' nuclease hypersensitive sites flanking the globin gene liberates a fragment from between these sites that sediments normally. We conclude that the hypersensitive sites per se are responsible for the reduction in sedimentation rate. The non-nucleosomal DNA segments appear to be too long to be incorporated into the chromatin solenoid and thus create spacers between separate solenoidal elements in the chromatin, which can account for its hydrodynamic behaviour.

Inherited antithrombin III (ATIII) deficiency causes a life-long tendency to venous thromboembolism, which is often recurrent and may be life-threatening. In contrast, the clinical importance of acquired ATIII deficiency, whether spontaneous or associated with estrogen-containing oral contraceptive treatment, remains uncertain. Moderately reduced ATIII activity before or immediately after surgery is neither sensitive nor specific for a high risk of postoperative venous thromboembolism (VTE), while moderately reduced ATIII activity during heparin treatment for VTE fails to indicate an unusually large heparin requirement or to predict recurrence. In the absence of good clinical trials, the value of ATIII replacement therapy also remains obscure; its use in congenital deficiency is largely based on anecdote, and while it may cause more rapid correction of the hemostatic defect in patients with disseminated intravascular coagulation (DIC), any improvement in morbidity or mortality resulting from ATIII replacement remains to be demonstrated.

To test the hypothesis that binding to an endogenous heparin-like substance controls breakdown of antithrombin III (ATIII) in vivo, the metabolic behavior of a commercial ATIII concentrate was investigated in three normal volunteers and five subjects with hereditary ATIII deficiency. The concentrate, purified to homogeneity as evidenced by sodium dodecyl sulfate--gel electrophoresis, was a 2:1 mixture of functional ATIII with heparin cofactor activity and dysfunctional ATIII incapable of binding enzymes or heparin. Each subject received intravenously a dose of 75 U/kg of ATIII activity together with iodine 125-labeled tracer. Daily fractional catabolic rates calculated from the three-exponential disappearance curves of plasma radioactivity were similar in all investigated subjects and were within the range obtained in studies using functionally homogeneous tracer. Although all subjects had markedly increased ATIII levels after injection of the concentrate, the relative sizes of their ATIII distribution pools resembled those reported previously for people with normal ATIII concentration. There was, however, a noticeably faster disappearance from plasma of excess functional ATIII compared with that of ATIII antigen, with mean half-lives of 47.5 +/- 9 hours and 62.3 +/- 8 hours, respectively. Assuming that antigenic ATIII represented both functional inhibitor and dysfunctional ATIII incapable of binding heparin, these data are consistent with the supposition that interaction with endogenous heparin or a similar substance may regulate a catabolic pathway marking ATIII for destruction.

Antithrombin-III Denver is a mutant protein which differs from the normal in being defective in serine protease binding (Sambrano, J. E., Jacobson, L. J., Reeve, E. B., Manco-Johnson, M. J., and Hathaway, W. E. (1986) J. Clin. Invest. 77, 887-893). It was isolated from the blood of an individual heterozygous for the abnormal gene by: affinity separation on heparin-Sepharose to obtain an antithrombin fraction, and gel filtration of the species present following complexing of the antithrombin fraction with a small excess of thrombin. The reduced, S-carboxymethylated protein formed a mixture of soluble tryptic peptides which was fractionated on Vydac C18. A single, unique peptide not present in a parallel experiment with normal antithrombin-III was isolated. This peptide was identified by sequence analysis and synthesis to correspond to residues 394-399 in the known sequence of the inhibitor, with leucine replacing reactive site P'1 residue Ser394. Although chromatograms of the tryptic peptides from the normal and mutant proteins were otherwise indistinguishable, the existence of additional residue replacements is not excluded. Measurements of the rate of thrombin binding by the mutant protein with p-aminobenzamidine as a fluorescent indicator showed that the second-order rate constant is reduced drastically. Meaningful measurements with the mutant protein could only be made in the presence of heparin and revealed a reduction of about 4000-fold in the rate constant.

Amide derivatives of a carboxylic acid congener of 1,3-dialkylxanthine, having a 4-[(carboxymethyl)oxy]phenyl substituent at the 8-position, have been synthesized in order to identify potent antagonists at A2-adenosine receptors stimulatory to adenylate cyclase in platelets. Distal structural features of amide-linked chains and the size of the 1,3-dialkyl groups have been varied. 1,3-Diethyl groups, more than 1,3-dimethyl or 1,3-dipropyl groups, favor A2 potency, even in the presence of extended chains attached at the 8-(p-substituted-phenyl) position. Polar groups, such as amines, on the chain simultaneously enhance water solubility and A2 potency. Among the most potent A2 ligands are an amine congener, 8-[4-[[[[(2-aminoethyl)amino]carbonyl]methyl]oxy]phenyl]- 1,3-diethylxanthine, and its D-lysyl conjugate, which have KB values of 21 and 23 nM, respectively, for the antagonism of N-ethyl-adenosine-5'-uronamide-stimulated adenylate cyclase activity in human platelet membranes. Strategies for the selection and tritiation of new radioligands for use in competitive binding assays at A2-adenosine receptors have been considered.