A chemokine expressed in lymphoid high endothelial venules promotes the adhesion and chemotaxis of naive T lymphocytes

Preferential homing of naive lymphocytes to secondary lymphoid organs is thought to involve the action of chemokines, yet no chemokine has been shown to have either the expression pattern or the activities required to mediate this process. Here we show that a chemokine represented in the EST database, secondary lymphoid-tissue chemokine (SLC), is expressed in the high endothelial venules of lymph nodes and Peyer's patches, in the T cell areas of spleen, lymph nodes, and Peyer's patches, and in the lymphatic endothelium of multiple organs. SLC is a highly efficacious chemoattractant for lymphocytes with preferential activity toward naive T cells. Moreover, SLC induces firm adhesion of naive T lymphocytes via beta2 integrin binding to the counter receptor, intercellular adhesion molecule-1, a necessary step for lymphocyte recruitment. SLC is the first chemokine demonstrated to have the characteristics required to mediate homing of lymphocytes to secondary lymphoid organs. In addition, the expression of SLC in lymphatic endothelium suggests that the migration of lymphocytes from tissues into efferent lymphatics may be an active process mediated by this molecule.

Ligation of L-selectin on T lymphocytes activates beta1 integrins and promotes adhesion to fibronectin

Lymphocyte recirculation is dependent on families of adhesion molecules expressed on lymphocytes and their sequential interaction with ligands expressed on high endothelial venules in secondary lymphoid organs such as peripheral lymph nodes. By binding its carbohydrate-based ligands, L-selectin initiates this cascade of molecular interactions, supporting the rolling of lymphocytes along high endothelial venules. Subsequent activation of lymphocyte integrins leads to cell arrest followed by lymphocyte extravasation. Here, we demonstrate stimulated adhesion of PBL and Jurkat T cells to immobilized fibronectin following treatment with (1) GlyCAM-1, a physiologic ligand for L-selectin, and (2) cross-linked anti-L-selectin mAbs. We also utilize a solution binding assay to detect early changes in integrin activity, including affinity modulation and/or integrin clustering, and distinguish these from later postreceptor binding events such as changes in cell shape and spreading. With the Jurkat cell line, GlyCAM-1 and fucoidin (an L-selectin ligand mimetic) induce the binding of soluble fibronectin. In contrast, stimulation through the Jurkat TCR fails to promote binding to soluble ligand even though TCR cross-linking markedly enhances adhesion to immobilized fibronectin. These data suggest that L-selectin and the TCR promote adhesion through distinct mechanisms. Finally, we demonstrate that beta1 integrins are preferentially activated on naive T cells through the L-selectin pathway. Together with our previous studies showing similar activation of beta2 integrins on the naive T cell subset, these data suggest that signals delivered though L-selectin participate in the preferential recruitment of these cells to peripheral lymph nodes.

Ligation of L-selectin on T lymphocytes activates beta1 integrins and promotes adhesion to fibronectin

Lymphocyte recirculation is dependent on families of adhesion molecules expressed on lymphocytes and their sequential interaction with ligands expressed on high endothelial venules in secondary lymphoid organs such as peripheral lymph nodes. By binding its carbohydrate-based ligands, L-selectin initiates this cascade of molecular interactions, supporting the rolling of lymphocytes along high endothelial venules. Subsequent activation of lymphocyte integrins leads to cell arrest followed by lymphocyte extravasation. Here, we demonstrate stimulated adhesion of PBL and Jurkat T cells to immobilized fibronectin following treatment with (1) GlyCAM-1, a physiologic ligand for L-selectin, and (2) cross-linked anti-L-selectin mAbs. We also utilize a solution binding assay to detect early changes in integrin activity, including affinity modulation and/or integrin clustering, and distinguish these from later postreceptor binding events such as changes in cell shape and spreading. With the Jurkat cell line, GlyCAM-1 and fucoidin (an L-selectin ligand mimetic) induce the binding of soluble fibronectin. In contrast, stimulation through the Jurkat TCR fails to promote binding to soluble ligand even though TCR cross-linking markedly enhances adhesion to immobilized fibronectin. These data suggest that L-selectin and the TCR promote adhesion through distinct mechanisms. Finally, we demonstrate that beta1 integrins are preferentially activated on naive T cells through the L-selectin pathway. Together with our previous studies showing similar activation of beta2 integrins on the naive T cell subset, these data suggest that signals delivered though L-selectin participate in the preferential recruitment of these cells to peripheral lymph nodes.

An ELISA for selectins based on binding to a physiological ligand

Members of the selectin family of adhesion receptors, consisting of L-, P- and E-selectin, mediate the initial interaction between leukocytes and endothelium during leukocyte trafficking from the blood into tissue sites. These receptors have attracted great attention in recent years due to their participation in a number of acute and chronic inflammatory diseases. We describe here a new ELISA that measures the binding between selectin-IgG chimeras and a physiological ligand for L-selectin and can be used to screen selectin inhibitors. The ligand used is a mucin-like glycoprotein known as GlyCAM-1, which is derived from high endothelial venules in secondary lymphoid organs. We demonstrate binding of all three selectins to GlyCAM-1 and demonstrate that the binding interactions satisfy a number of important criteria. The advantage of this ELISA over previous assays is that a macromolecular physiological ligand is employed, rather than a fortuitous or simplified carbohydrate ligand. Thus, the protein-carbohydrate interactions, as well as other interactions contributing to ligand recognition, can be investigated. The assay is suitable for high-throughout screening of compounds and may find use in the identification of selectin antagonists with anti-inflammatory potential.

Retinopathy of prematurity in multiple-gestation, very low birth weight infants

Ninety-nine infants from multiple gestation births and weighing < or = 1500 g at birth were matched with infants from single births to clarify the relationship of multiple gestation to retinopathy of prematurity (ROP). There was no significant difference in the incidence of ROP between the twins and the singletons (relative risk [RR] = 0.84, 95% confidence intervals [CI] = 0.61, 1.16). Logistic regression analysis confirmed that very low birth weight (VLBW), not single or multiple gestation, was the most significant predictor of ROP occurrence in either group. In 27 pairs of twin siblings from the original twin group, where both weighed < or = 1500 g at birth, we found that the second-born twin seemed at higher risk for developing ROP, but logistic regression showed that the lower birth weight of the second twin, not birth order, was the more significant predictor of ROP. These results indicate that ROP screening in VLBW twins may be conducted according to the same standard protocols as for singletons.

Coronary vasodilator reserve in primary and secondary left ventricular hypertrophy. A study with positron emission tomography

OBJECTIVES

Coronary vasodilator reserve is reduced in hypertrophic cardiomyopathy and secondary left ventricular hypertrophy despite angiographically normal coronaries. The aim of the present study was to assess whether quantitative differences exist between these conditions.

METHODS

Using positron emission tomography with H2(15)O, myocardial blood flow was measured at baseline and following intravenous dipyridamole (0.56 mg.kg-1) in 12 hypertrophic cardiomyopathy patients (age 34 (11) years, mean (SD), all male), 16 secondary left ventricular hypertrophy patients (age 58 (20) years, P < 0.01 vs hypertrophic cardiomyopathy; 10 female) and 40 normal controls (age 54 (20), 13 female). In view of the known decline of post-dipyridamole myocardial blood flow with age, myocardial blood flow was compared between the patient groups and appropriately matched subsets of the total control group.

RESULTS

Baseline myocardial blood flow in the hypertrophic cardiomyopathy patients was 0.82 (0.23) ml.min-1.g-1 vs 0.94 (0.14) ml.min-1.g-1 in its matched control group, P = ns. For the secondary left ventricular hypertrophy patient group, baseline myocardial blood flow was 1.17 (0.40) ml.min-1.g-1 vs 1.06 (0.28) ml.min-1.g-1 for the secondary left ventricular hypertrophy matched control group, P = ns. Following dipyridamole, myocardial blood flow was 1.64 (0.44) ml.min-1.g.-1 in hypertrophic cardiomyopathy patients vs 3.50 (0.95) ml.min-1.g-1 for the hypertrophic cardiomyopathy matched control group, P = 0.0001. For the left ventricular hypertrophy patients, post-dipyridamole myocardial blood flow was 2.27 (0.60) ml.min-1.g-1 vs 2.94 (1.29) ml.min-1.g-1 for the left ventricular hypertrophy controls, P = 0.06. Coronary vasodilator reserve (dipyridamole-myocardial blood flow/baseline-myocardial blood flow) was 2.05 (0.61) for hypertrophic cardiomyopathy patients vs 3.81 (0.98) for the hypertrophic cardiomyopathy controls (P = 0.0001, patients vs controls) and 2.06 (0.62) for left ventricular hypertrophy patients vs 2.90 (1.38) for the left ventricular hypertrophy controls, P < 0.03 patients vs controls. After correction of baseline myocardial blood flow for baseline heart rate x systolic pressure product, coronary vasodilator reserve for the hypertrophic cardiomyopathy patients was 2.06 (1.06) vs 4.34 (1.54) for the hypertrophic cardiomyopathy controls. P = 0.0002 and in the secondary left ventricular hypertrophy patients, the values were 2.13 (0.64) vs 2.89 (1.42) in the secondary left ventricular hypertrophy controls, P < 0.05.

CONCLUSION

In both hypertrophic cardiomyopathy and secondary left ventricular hypertrophy, the computed coronary vasodilator reserve is impaired, even after correction for baseline cardiac work. However, the extent of the reduction is greater in the hypertrophic cardiomyopathy patients. In the blunting of vasodilator reserve of secondary left ventricular hypertrophy, the patients' greater hyperaemic response is partly offset by the higher baseline myocardial blood flow.

L-selectin-carbohydrate interactions: relevant modifications of the Lewis x trisaccharide

Protein-carbohydrate interactions are known to mediate cell-cell recognition and adhesion events. Specifically, three carbohydrate binding proteins termed selectins (E-, P-, and L-selectin) have been shown to be essential for leukocyte rolling along the vascular endothelium, the first step in the recruitment of leukocytes from the blood into inflammatory sites or into secondary lymphoid organs. Although this phenomenon is well-established, little is known about the molecular-level interactions on which it depends. All three selectins recognize sulfated and sialylated derivatives of the Lewis x [Le(x):Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc] and Lewis a [Le(a): Gal beta 1-->3(Fuc alpha 1-->4)GlcNAc] trisaccharide cores with affinities in the millimolar range, and it is believed that variants of these structures are the carbohydrate determinants of selectin recognition. Recently it was shown that the mucin GlyCAM-1, a secreted physiological ligand for L-selectin, is capped with sulfated derivatives of sialyl Lewis x [sLe(x): Sia alpha 2-->3Gal beta 1-->4(Fuc alpha 1-->3)GlcNAc] and that sulfation is required for the high-affinity interaction between GlyCAM-1 and L-selectin. To elucidate the important sites of sulfation on Le(x) with respect to L-selectin recognition, we have synthesized six sulfated Le(x) analogs and determined their abilities to block binding of a recombinant L-selectin-Ig chimera to immobilized GlyCAM-1. Our results suggest that 6-sulfo sLe(x) binds to L-selectin with higher affinity than does sLe(x) or 6'-sulfo sLe(x) and that sulfation of sLe(x) capping groups on GlyCAM-1 at the 6-position is important for L-selectin recognition.

Myocardial beta adrenoceptor density in primary and secondary left ventricular hypertrophy

OBJECTIVES

Myocardial beta-adrenoceptor density has been found to be reduced in hypertrophic cardiomyopathy, even when systolic function is preserved. Our purpose in the current study was to investigate whether beta-adrenoceptor down-regulation was unique to hypertrophic cardiomyopathy, or is also present in secondary myocardial hypertrophy.

METHODS

Myocardial beta-adrenoceptor density was measured in 11 patients with hypertrophic cardiomyopathy, eight patients with left ventricular hypertrophy secondary to arterial hypertension or aortic valve disease and 18 normal control subjects, using positron emission tomography with 11C-CGP-12177 as the myocardial beta-adrenoceptor ligand.

RESULTS

Reflecting the natural incidence of the conditions, the age of the hypertrophic cardiomyopathy patients was 37 (10) [mean (SD), range 20-51] years and that of the secondary hypertrophy patients 64 (18), [range 26-80] years; P < 0.01. The controls' ages were 50 (13), [range 21-65] years; however, since beta-adrenoceptor density is known to be influenced by age, the controls' data was split into groups matched to the hypertrophic cardiomyopathy and secondary hypertrophy patient sets. For the hypertrophic cardiomyopathy patients, mean left ventricular beta-adrenoceptor was 7.70 (1.86) pmol.g-1 compared to 10.17 (2.44) pmol.g-1 for a matched set of 15 controls; P < 0.01. In secondary left ventricular hypertrophy, beta-adrenoceptor was 6.35 (1.70) pmol.g-1 compared to 9.16 (2.00) pmol.g-1 for a matched set of 10 controls; P < 0.01. Plasma noradrenaline was 5.5 (2.2) nmol.l-1 in hypertrophic cardiomyopathy and 2.5 (1.0) nmol.l-1 for the matched controls; P < 0.01. The results for adrenaline were 2.2 (1.1) vs 0.4 (0.3) nmol.l-1 respectively; P < 0.001. For the secondary hypertrophy patients, the corresponding figures were 2.5 (1.2) vs 2.5 (1.0) nmol.l-1 for noradrenaline for patients and controls respectively (P = ns); and for adrenaline 0.2 (0.1) and 0.3 (0.2) nmol.l-1 respectively, P = ns. On multiple regression analysis, no relationships could be demonstrated amongst plasma catecholamines, beta-adrenoceptor, myocardial blood flow and echocardiographic E/A ratio and fractional shortening.

CONCLUSION

Myocardial beta-adrenoceptor density appears to be comparably decreased in both primary and secondary left ventricular hypertrophy in the presence of preserved left ventricular systolic function.

GlyCAM-1, a physiologic ligand for L-selectin, activates beta 2 integrins on naive peripheral lymphocytes

Naive T cells are selectively recruited from the blood into peripheral lymph nodes during lymphocyte recirculation. L-selectin, a lectin-like receptor, mediates the initial attachment of lymphocytes to high endothelial venules (HEV) in lymph nodes. A subsequent step involving the activation of beta 2 integrins has been proposed to facilitate firm adhesion, but the activating signals are poorly understood. We report here that either antibody-mediated cross-linking of L-selectin on human lymphocytes or treatment of the cells with GlyCAM-1, an HEV-derived, secreted ligand for L-selectin, stimulates their binding to ICAM-1 through the beta 2 integrin pathway. Furthermore, GlyCAM-1 causes the rapid expression of a neoepitope on beta 2 integrins associated with a high-avidity state. Naive (CD45RA+), but not memory (CD45R0+) lymphocytes, respond to L-selectin cross-linking or GlyCAM-1 treatment. Thus, the complexing of L-selectin by specific ligands may provide key signals to naive lymphocytes, contributing to their selective recruitment into peripheral lymphoid organs.

Effect of alpha 1-adrenoceptor blockade on resting and hyperemic myocardial blood flow in normal humans

In the present study we aimed to assess the effect of alpha 1-adrenoceptor blockade on resting and hyperemic myocardial blood flow in normal humans. Myocardial blood flow, at baseline and after dipyridamole, was measured with positron emission tomography and 15O-labeled water in 11 normal volunteers at control and during alpha 1-blockade with doxazosin. Baseline myocardial blood flow during alpha 1-blockade was not different from control, whereas coronary resistance was significantly lower (73.48 +/- 18.31 vs. 89.84 +/- 27.96 mmHg.min.ml-1.g-1; P < 0.05). After dipyridamole, myocardial blood flow during alpha 1-blockade was significantly higher (3.50 +/- 0.75 vs. 2.58 +/- 0.54 ml.min-1.g-1; P < 0.01) and coronary resistance lower (25.30 +/- 7.37 vs. 33.89 +/- 7.04 mmHg.min.ml-1.g-1; P < 0.01) compared with control. In conclusion, in normal humans, dipyridamole-induced increase in myocardial blood flow is limited by alpha 1-mediated coronary vasoconstriction.

Purification and quantification of L-selectin-reactive GlyCAM-1 from mouse serum

GlyCAM-1 is an endothelial-derived mucin found in the conditioned medium of organ-cultured lymph nodes and in serum. It is a ligand for L-selectin, but also interacts with P and E-selectin. It may play a role in the modulation of leukocyte trafficking into secondary lymphoid tissues as well as chronic inflammatory sites. Here we report the development of an ELISA that quantifies GlyCAM-1 in complex biological fluids such as serum. The ELISA response is linear over a concentration range of 13-800 ng/ml. The level of GlyCAM-1 in mouse serum was found to be 1.3-1.6 micrograms/ml. Using mouse serum as starting material, we report a rapid and efficient purification scheme for the isolation of biologically active GlyCAM-1. This material may now be used to address the biological functions of GlyCAM-1 and to further define its structural features.

Myocardial beta-adrenoceptor density and plasma catecholamines in syndrome X

Recent research has cast doubt on the ischemic hypothesis of etiology of syndrome X (anginal pain, ischemic-like changes in the stress electrocardiogram, but normal coronary arteriogram). Abnormalities of pain perception have been shown and abnormal sympathetic nervous system activation has also been implicated. The aim of this study was to test the hypothesis that downregulation of myocardial beta adrenoceptors is demonstrable in patients with syndrome X. Such downregulation would be consistent with raised myocardial catecholamine concentrations. We performed positron emission tomography with (11)C-CGP-12177 to measure beta-adrenoceptor density. Plasma catecholamines were sampled simultaneously and assayed using high-performance liquid chromatography. Twenty syndrome X patients (11 female, age 57 +/- 9 SD years, range 33 to 69) and 18 matched controls (9 women, age 50 +/- 13 years, range 25 to 65; p = NS vs patients) were studied. Myocardial beta-adrenoceptor density did not differ between syndrome X patients and controls: 8.0 (1.9) pmol/g for patients versus 8.3 (2.1) pmol/g for controls; p = 0.62. No differences were found between patients and controls for plasma norepinephrine (2.82 [1.07] and 2.76 [1.18] nM, respectively; p = 0.89) or for epinephrine (0.29 [0.14] and 0.30 [0.20] nM, respectively; p = 0.84). In patients with syndrome X, beta-adrenoceptor density is normal and, by inference, myocardial catecholamines would also be normal. This weakens the case for a generalized enhancement of sympathetic activation in this disorder, although increased sympathetic reactivity during actual episodes of chest pain remains a possibility.

Silent ischemia as a central problem: regional brain activation compared in silent and painful myocardial ischemia

OBJECTIVE

To test whether the silence of painless myocardial ischemia is caused by abnormal handling by the central nervous system of afferent messages from the heart.

DESIGN

Nonrandomized study.

SETTING

A tertiary referral center (postgraduate medical school).

PATIENTS

2 matched groups of nondiabetic patients with coronary artery disease. Group A consisted of nine patients with reproducible stress-induced angina; group B consisted of nine patients with reproducible stress-induced myocardial ischemia but no angina.

INTERVENTIONS

Intravenous placebo infusion and low-dose (5 and 10 micrograms/ kg per minute) and high-dose (20 to 35 micrograms/kg per minute) dobutamine infusions.

MEASUREMENTS

Positron emission tomography was used to measure regional cerebral blood flow changes as an index of neuronal activation during painful and silent myocardial ischemia induced by intravenous dobutamine.

RESULTS

Regional cerebral blood flow changes during myocardial ischemia were compared with those during baseline conditions and during placebo infusion. During myocardial ischemia, regional cerebral blood flow increased bilaterally in the thalami and prefrontal, basal frontal, and ventral cingulate corticles in patients in group A. Both thalami were activated in group B, but cortical activation was limited to the right frontal region. A formal comparison of groups A and B showed significant differences (P < 0.01) in activation of the basal frontal cortex, ventral cingulate cortex, and left temporal pole. In both groups, thalamic regional cerebral blood flow remained increased after the symptoms and signs of ischemia had ceased.

CONCLUSIONS

Bilateral activation of the thalamus can be shown in both angina and silent ischemia; thus, peripheral nerve dysfunction cannot completely explain silent ischemia. Frontal cortical activation appears to be necessary for the sensation of pain. Abnormal central processing of afferent pain messages from the heart may play a determining role in silent myocardial ischemia.

Uptake of [N-methyl-11C]propionyl-L-carnitine (PLC) in human myocardium

We studied the uptake of propionyl-L-carnitine from plasma by the myocardium in 10 human subjects using positron emission tomography. Propionyl-L-carnitine was labeled in the N-methyl position with carbon-11 (T1/2 = 20.4 min) and administered i.v. in trace amounts. The uptake of the radiolabel by the myocardium was then scanned over a period of 1 1/2 h. The activity-time course of the tracer in blood and plasma and the exchange of the label in plasma between propionyl carnitine, acetyl carnitine and free carnitine was followed during the scans. Myocardial blood flow was also measured in the same subjects. The results show an exchange of the tracer between the myocardium and plasma, and they show an apparently irreversible component of uptake, a result consistent with the incorporation of the label into relatively large intracellular carnitine pools.

Two selectins converge on sulphate. Leukocyte adhesion

Selectins mediate the attachment of leukocytes to endothelial cells and to platelets under conditions of blood flow. Sulphation of the ligands for two of the selectins is required for optimal cell-cell interactions.

Fundus pigmentation in retinopathy of prematurity

OBJECTIVE

A prospective study design was used to investigate the association between different degrees of fundus pigmentation and the indicence of retinopathy of prematurity (ROP) among very low birth weight infants in a large neonatal intensive care unit.

METHODS

The study group consisted of 161 infants weighing 1500 g or less at birth and included all infants born from 1988 to 1990 who survived at least 10 weeks. Presence or lack of any acute stage ROP was determined by weekly ophthalmological examination from the age of 4 weeks. The degree of fundus pigmentation was recorded for each infant during the first examination.

RESULTS

Infants with dark fundus pigmentation were found to be at half the risk of developing ROP as compared with infants having light/medium fundus pigmentation (relative risk = 0.5; 95% confidence interval = 0.2-1.1). When controlled for birth weight, gestational age, length of oxygen therapy, and ethnic group in multivariate analysis, dark pigmentation was an independent and statistically significant protective factor (odds ration = 0.09, 95% confidence interval = 0.02-0.06). None of the infants with Stage III ROP or higher had dark pigmentation.

CONCLUSION

We speculate that large amounts of melanin in the retinal pigment epithelium or choroid may protect the dark-pigmented very low birth weight infant from developing ROP.

Calcium-dependent lectin activity with novel distribution on thymocyte subsets

In this study we use carbohydrate probes to search for novel cell surface lectins in the immune system. Many carbohydrate binding proteins are members of the C-type lectin superfamily, whose ligand binding is dependent on calcium. To identify potential new members of this superfamily, fluorescein-conjugated carbohydrate polymers were used to probe for calcium-dependent cell surface binding. This approach offers advantages over the use of monoclonal antibody probes since only carbohydrate binding proteins would be identified. We have identified a cell surface lectin, referred to as thy-lec, detected by the probe fucoidan-fuorescein isothiocyanate. This calcium-dependent lectin has a novel distribution on thymocyte subsets. It is present on the surface of immature CD4+8+ and on large, cycling CD4-8- cells and CD8+4- cells, but not on small, mature phenotype CD8+4- or CD4+8- thymocytes. This lectin is not found on mature T cells or other leukocytes in lymph nodes, spleen or bone marrow. It is proposed that this novel cell surface has a function in the maturation of T cells in the thymus.

Modulation of L-selectin ligand expression during an immune response accompanying tumorigenesis in transgenic mice

Immune surveillance depends on lymphocyte access to tissue. Lymphocytes emigrate from blood when adhesion receptors such as L-selectin and the alpha 4 beta 7 integrin on these cells bind to ligands expressed on venular endothelium. Among transgenic mouse lines expressing an oncoprotein (Tag) in islet beta cells, some recognize Tag as nonself. In these mice, Tag expression elicits both beta cell hyperplasia with subsequent progression to tumors and lymphocytic infiltration. Endothelial ligands for L-selectin and alpha 4 beta 7 were upregulated in infiltrated islets in these transgenic mice. These ligands were not expressed in tumors, which were devoid of lymphocytic infiltration. In contrast, the adhesion molecules PECAM-1, ICAM-1, and VCAM-1 were expressed on endothelium in both noninfiltrated tumors and infiltrated islets. Thus, upregulation of expression of endothelial ligands for L-selectin and alpha 4 beta 7 may contribute to autoimmune infiltration. Repression of expression of these same ligands may be involved in the failure of tumor immunity.

Sulfated disaccharide inhibitors of L-selectin: deriving structural leads from a physiological selectin ligand

The selectins are a family of three adhesion molecules (L-, P-, and E-) that direct the interaction of circulating leukocytes with endothelial cells during the first step in recruitment to tissue sites. Their involvement in inflammatory disease makes the selectins attractive targets for anti-inflammatory therapy. The sialyl Lewis x tetrasaccharide binds weakly to all three selectins and has demonstrated anti-inflammatory activity in vivo. However, the synthetic difficulties inherent to sialylated and fucosylated oligosaccharides motivate the search for alternative antagonists. Here we demonstrate that information gained from the biochemical analysis of a physiological selectin ligand can provide new leads for small molecule design. Previous structural analysis of the oligosaccharide chains on GlyCAM-1, an endothelial-derived ligand for L-selectin, revealed two novel structures: 6'-sulfo sialyl Lewis x and 6-sulfo sialyl Lewis x. The sulfate esters on these structures are thought to be essential for high-affinity binding to L-selectin. By incorporating sulfate esters on the analogous positions of the disaccharide lactose, we generated a simple small molecule (lactose 6',6-disulfate) with greater inhibitory potency for L-selectin than sialyl Lewis x.

Effect of aging on myocardial perfusion reserve

Myocardial perfusion reserve (hyperemic divided by basal myocardial blood flow) describes vasodilator responsiveness of coronary-resistive vessels. The effect of aging and gender on myocardial perfusion reserve remains controversial.

METHODS

We studied 56 normal volunteers (21 women, 35 men; aged 50 +/- 20 yr, range 21-86 yr) with 15O-water PET to measure myocardial blood flow during basal and hyperemic states with intravenous dipyridamole (0.56 mg/kg, n = 46) or adenosine (140 micrograms/kg/min, n = 10). For comparative analysis, patients were grouped according to age: < 30 yr (n = 11), 30-49 yr (n = 18), 50-69 yr (n = 15) and > or = 70 yr (n = 12).

RESULTS

Overall, basal flow was 1.00 +/- 0.26 ml/min/g and hyperemic flow was 3.31 +/- 1.38 ml/min/g, resulting in a myocardial perfusion reserve of 3.38 +/- 1.35. There was an increase in basal flow with age (r = 0.45, p < 0.025), although hyperemic flow was only lower in patients > or = 70 yr, causing a significant reduction in myocardial perfusion reserve: 3.54 +/- 0.96 in < 30 yr, 4.23 +/- 1.35 in 30-49 yr, 3.51 +/- 1.21 in 50-69 yr and 1.94 +/- 0.46 in > or = 70 yr (p < 0.05 versus all groups < 70 yr).

CONCLUSION

Myocardial blood flow during basal and hyperemia conditions are roughly comparable up to 60 yr of age. Above this age, there is significant increase in basal flow associated with an increase in systolic blood pressure. Above 70 yr, there is a significant reduction in hyperemic flow, and thus myocardial perfusion reserve independent of hemodynamic response to vasodilator stress.