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Biomedical subjects

N N Kahn

Publications and source records attributed to N N Kahn.

16 recordsLinked to original sources
PubMed1996

Loss of high-affinity prostacyclin receptors in platelets and the lack of prostaglandin-induced inhibition of platelet-stimulated thrombin generation in subjects with spinal cord injury.

Coronary artery disease is a leading cause of death in individuals with chronic spinal cord injury (SCI). However, platelets of those with SCI (n = 30) showed neither increased aggregation nor resistance to the antiaggregatory effects of prostacyclin when compared with normal controls (n = 30). Prostanoid-induced cAMP synthesis was similar in both groups. In contrast, prostacyclin, which completely inhibited the platelet-stimulated thrombin generation in normal controls, failed to do so in those with SCI. Scatchard analysis of the binding of [3H]prostaglandin E1, used as a prostacyclin receptor probe, showed the presence of one high-affinity (Kd1 = 8.11 +/- 2.80 nM; n1 = 172 +/- 32 sites per cell) and one low-affinity (Kd2 = 1.01 +/- 0.3 microM; n2 = 1772 +/- 226 sites per cell) prostacyclin receptor in normal platelets. In contrast, the same analysis in subjects with SCI showed significant loss (P < 0.001) of high-affinity receptor sites (Kd1 = 6.34 +/- 1.91 nM; n1 = 43 +/- 10 sites per cell) with no significant change in the low affinity-receptors (Kd2 = 1.22 +/- 0.23; n2 = 1820 +/- 421). Treatment of these platelets with insulin, which has been demonstrated to restore both of the high- and low-affinity prostaglandin receptor numbers to within normal ranges in coronary artery disease, increased high-affinity receptor numbers and restored the prostacyclin effect on thrombin generation. These results demonstrate that the loss of the inhibitory effect of prostacyclin on the stimulation of thrombin generation was due to the loss of platelet high-affinity prostanoid receptors, which may contribute to atherogenesis in individuals with chronic SCI.

Adult↗
PubMed1995

Insulin-induced release of plasminogen activator from human blood platelets.

Incubation of washed platelets in Tyrode buffer, pH 7.5, with insulin (200 microU/ml) and CaCl2 (1.2 mM) at 37 degrees C for 3 h resulted in a threefold increase of plasminogen activator activity in the supernatant over the basal level as determined by both the amidolytic assay and the proteolysis of alpha-casein through the formation of plasmin from plasminogen. This plasminogen activator showed no plasmin-like activity and was inhibited by anti-tissue plasminogen activator antibody as well as by type 1 plasminogen activator inhibitor. The substrate specificity and the inhibition of the enzymic activity by various inhibitors indicated that the platelet plasminogen activator (pPA) was related to tissue-type plasminogen activator of relative molecular weight 56,000. Fibrinolytic activity of pPA and its insulin-dependent release were demonstrated by the shortening of euglobulin lysis time and by the clot lysis time of platelet-rich plasma from normal and type I diabetes mellitus patients. Treatment of platelet membranes with insulin also increased the release of pPA. Increased levels of adenosine 3',5'-cyclic monophosphate (cAMP) in platelets by incubation with various agents completely inhibited the insulin-induced release of the activator. On the other hand, inhibition of platelet aggregation by aspirin had no effect on the release of pPA, indicating that the effect of cAMP was not due to the inhibition of platelet aggregation by the nucleotide.

Alprostadil↗
PubMed1994

Transient decrease of binding of insulin to platelets in acute ischemic heart disease.

The specific binding sites of 125I-insulin in platelets from nondiabetic patients with acute myocardial infarction and unstable angina pectoris was significantly decreased (192 +/- 84/cell) during the acute ischemic condition when compared with normal platelets (496 +/- 76/cell; p < 0.001, n = 9). A relatively low mean plasma insulin level (20 microU/mL) with an elevated mean glucose level (130 mg/dL) was noted. The decreased binding of insulin and the relatively low mean plasma insulin level during the acute ischemic condition improved into the normal range during 8 to 12 weeks of recuperation. The decrease of insulin binding sites in the acute phase and their subsequent increase during recovery were directly related to the hormone-induced increase in sensitivity to prostaglandin E1 through the stimulation of adenosine 3',5'-cyclic monophosphate formation in platelets by the prostanoid.

Acute Disease↗
PubMed1993

Inhibition of platelet aggregation and the stimulation of prostacyclin synthesis by insulin in humans.

An intravenous bolus injection of insulin (35.5 microM) followed by an infusion of insulin (0.53 microM.kg-1.h-1) for 2.5 h (which maintained plasma levels between 0.71 nM to 1.4 nM) in normal fasting volunteers (n = 16), increased [3H]prostaglandin E1 (a probe for prostacyclin) binding to platelets by two- to threefold over the control. Scatchard analyses showed that the increased binding was due to the increase of both high and low affinity receptor numbers with little change in the receptor affinities. Similar results were obtained by using [3H]prostacyclin as the radioligand. The increased binding was associated with more than a twofold decrease of the minimum concentration of prostanoid needed to inhibit aggregation of platelets through the increased formation of adenosine 3',5'-cyclic monophosphate. Furthermore, the infusion increased the mean plasma prostacyclin level from 12.10 +/- 4.5 pM to 23.9 +/- 6.7 pM (n = 16; P < 0.001). These effects of insulin were at least partially direct, since the treatment of endothelial cells with insulin in tissue culture stimulated the production of the autacoid. Bolus injection of insulin (0.71 microM/kg) showed that the above effects of insulin could be demonstrated within 20 min after the injection, attained maximal ranges in approximately 60 min, and disappeared by 2-4 h.

Adult↗
PubMed1992

Normalization of impaired response of platelets to prostaglandin E1/I2 and synthesis of prostacyclin by insulin in unstable angina pectoris and in acute myocardial infarction.

The minimal inhibitory concentration of prostaglandin E1 (used as a probe for prostacyclin [PGI2]) needed to inhibit platelet aggregation (36 +/- 16 nM) in normal volunteers (n = 40) increased (64 +/- 30 nM) in patients (n = 46) with acute coronary artery disease. Bolus injection of insulin in 20 patients, 0.1 U/kg body weight 4 times a day (every 6 hours) for 7 days decreased the minimal inhibitory concentration of prostaglandin E1 from 64 +/- 30 to 26 +/- 12 nM (p less than 0.001). Twenty other patients who received only saline solution had no decrease in minimal inhibitory concentration of the prostanoid. The bolus injection of insulin also increased the plasma level of PGI2 (9 +/- 2 pM) two-fold in these patients (28 +/- 10 pM). Administration of aspirin inhibited the insulin-induced increase of plasma prostanoid level. Patients in the placebo group had no increase in plasma PGI2 level. The bolus injection of insulin administered only once to another group of patients (n = 6) demonstrated that the hormonal effects were maximally increased within an hour of insulin administration, and were directly related to the increased insulin level in plasma. These results indicated the feasibility of using physiologic quantities of insulin for controlling of platelet aggregation through resensitization of platelet response to prostaglandin and increased synthesis of PGI2 in vivo in acute coronary artery disease.

Angina, Unstable↗
PubMed1992

Down regulation of alpha 2 adrenergic receptor numbers in platelets by insulin.

Incubation of platelets from normal volunteers, who had not taken any medication at least for 2 weeks, with insulin (200 mu units/ml), resulted in the inhibition of the potentiation of ADP-induced platelet aggregation in the presence of (-)-epinephrine by 50-60% when compared with the control. The inhibitory effect of insulin was not related to the increased cyclic AMP level or decreased thromboxane A2 synthesis in these cells. It was found that the treatment of platelets with insulin decreased alpha 2 adrenergic receptors number of these cells from 413 +/- 92/platelet to 206 +/- 84/platelet as determined by Scatchard analysis of [3H]yohimbine binding. The affinity of the receptors (1.05 +/- 0.02 nM) remained essentially unchanged due to the treatment of platelets with the hormone (1.40 +/- 0.60 nM).

Blood Platelets↗
PubMed1991

Interaction of receptors for prostaglandin E1/prostacyclin and insulin in human erythrocytes and platelets.

Prostaglandin E1/I2 and insulin receptors of human erythrocyte and platelet are capable of modulating each other's activity. This modulation of the receptor activity and number in one system by a second receptor system in human platelet and erythrocyte seems to be beneficial. Insulin increases the PGE1 binding to platelets and thereby enhances the platelet antiaggregatory action of prostaglandin by increasing cyclic AMP levels. Similarly, PGE1 increases insulin binding to human erythrocyte, and thereby reduces the optimum concentration of insulin for a maximal reduction in membrane microviscosity. During ischemia the reduced response of platelets to the inhibitory effect of PGE1 or PGI2 relates to the impaired PGE1/I2 receptor activity. Treatment of these platelets with insulin at physiological concentrations can normalise the PGE1/I2 receptor activity. This review focuses on the relationship between the two receptor systems in human blood cells.

Alprostadil↗
PubMed1991

Restoration by insulin of impaired prostaglandin E1/I2 receptor activity of platelets in acute ischemic heart disease.

Treatment of normal platelet-rich plasma with a physiological amount of insulin (100 microunits/ml, optimum concentration) for 3 hours at 23 degrees C stimulated the binding of prostaglandin E1 by more than twofold (3,940 +/- 250 sites/10(8) platelets) compared with the nontreated, control platelet-rich plasma (1,590 +/- 265 sites/10(8) platelets). After platelet-rich plasma from patients with acute ischemic heart disease (n = 43), whose platelets showed impaired prostaglandin E1/I2 receptor activity (850 +/- 100 sites/10(8) platelets), was incubated with insulin (optimum amounts varied from 100 to 200 microunits/ml), the binding of the prostanoid was restored to normal levels (1,790 +/- 140 sites/10(8) platelets) in 75% of the cases. Twenty-five percent of the patients did not respond to the stimulatory effect of insulin. The increased binding of the prostanoid to the insulin-treated platelets also resulted in increased cyclic AMP levels both in normal subjects (44.14 +/- 3.1 pmol/10(8) [insulin-treated] platelets versus 16.35 +/- 2.91 pmol/10(8) [control] platelets) and in patients with acute ischemic heart disease (23.87 +/- 4.1 pmol/10(8) [insulin-treated] platelets versus 7.70 +/- 2.0 pmol/10(8) [control] platelets) by the prostanoid (1.0 microM). The treatment of platelet-rich plasma with the hormone decreased the minimum inhibitory concentration of the prostanoid from 34 +/- 14 to 15 +/- 9 nM (p less than 0.001) in the case of normal volunteers and from 49 +/- 15 to 32 +/- 11 nM (p = 0.002) in the case of "responder" patients. Insulin did not produce any effect on the inhibition of platelet aggregation by the prostaglandin in "nonresponder" patients. In the follow-up study, although the stimulatory effects of insulin on platelets from responder patients were improved to normal levels, the platelets from the nonresponder patients remained persistently unresponsive to the effect of the hormone.

Acute Disease↗
PubMed1990

Stimulation of prostaglandin E1 binding to human blood platelet membrane by insulin and the activation of adenylate cyclase.

Incubation of human platelet-rich plasma with physiological amounts of insulin resulted in the increase of the binding of prostaglandin E1 by more than 2-fold when compared to the control platelets. Scatchard analysis of the binding of the prostaglandin to the hormone-treated platelets showed that the increased binding was due to the increase of receptor numbers rather than the increase of affinity of the binding sites. The membranes prepared from the insulin-treated platelets also showed similar enhanced binding of the prostaglandin. However, addition of insulin directly to the membranes isolated from the platelets which had not been previously incubated with the hormone failed to show any effect. This increased binding of the prostanoid to the membranes prepared from the insulin-treated platelets resulted in the stimulation of adenylate cyclase by more than 2-fold when compared with the control of membrane preparation by the prostaglandin alone. In contrast, treatment of platelets with the hormone which increased the prostanoid binding to these cells did not influence the cyclic AMP phosphodiesterase activity of either the membrane or cytosolic fraction. The increase in the cellular level of cyclic AMP by prostaglandin E1 was 2-fold greater in the hormone-treated cells than in the case of untreated platelets stimulated by the agonist alone. The incubation of platelet-rich plasma with insulin, as expected, decreased the amount of prostaglandin E1 needed to inhibit platelet aggregation by more than 50% when compared to the control platelets.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1990

Impaired prostaglandin E1/I2 receptor activity of human blood platelets in acute ischemic heart disease.

The platelets from 74 patients with acute myocardial infarction or with unstable angina showed decreased prostaglandin E1/I2 receptor activity when compared with that of 56 normal volunteers by using [3H]prostaglandin E1 as a probe. In normals, Scatchard analyses showed the presence of one high-affinity-low-capacity (Kd1 = 9.0 +/- 1.2 nM [mean +/- SD]; n1 = 120 +/- 30 sites/cell) and one low-affinity-high-capacity (Kd2 = 1.1 +/- 0.5 microM; n2 = 1,460 +/- 250 sites/cell) prostaglandin E1/I2 receptor population in platelets. In contrast (p less than 0.01), platelets from patients showed decreased ligand binding (n1 = 40 +/- 20 sites/cell; n2 = 800 +/- 210 sites/cell) with little change in the affinity of the receptors (Kd1 = 7.50 +/- 1.6 nM; Kd2 = 0.68 +/- 0.24 microM). On the other hand, the platelets from the patients with dilated cardiomyopathy (n = 7) who were hospitalized for acute chest pain but had normal coronary arteries did not show any impairment of the receptor activity. The plasma prostacyclin level of the patients with acute ischemic heart disease was similar to that of normal volunteers; this finding indicated that the defective receptor function was not related to the prostaglandin receptors occupancy in vivo. The impaired receptor activity was temporary in nature. The follow-up studies showed that the prostaglandin receptor activity of the patients' platelets improved to "normal" levels within 2-8 weeks.(ABSTRACT TRUNCATED AT 250 WORDS)

Acute Disease↗
PubMed1990

Enhanced platelet adherence and aggregation in Chagas' disease: a potential pathogenic mechanism for cardiomyopathy.

Spasm and thrombosis of the coronary microcirculation has been implicated in the pathogenesis of the cardiomyopathy of Chagas' disease. We demonstrate that increases in platelet adherence and aggregation accompany Trypanosoma cruzi infection and may contribute to the observed microvascular pathology. Scanning electron microscopy and radiolabeled platelets studies revealed that platelet adherence to T. cruzi-infected human endothelial cells was significantly increased when compared to controls (P = 0.024). In in vitro experiments, we determined the influence of infection on prostacyclin production, a marker of endothelial cell perturbation. The basal levels of 6-keto-prostaglandin F1 alpha was significantly greater in the supernatant of infected endothelial cells than in those of uninfected endothelial cells (P less than 0.05). The influence of infection was assessed on platelet aggregation at days 5 and 12 post-infection in A/J mice. Platelets from T. cruzi-infected mice were 2-6-fold more sensitive to aggregation induced by adenosine diphosphate and sodium arachidonate than controls. Thromboxane B2 levels in the plasma of infected mice were greater than controls. These data support the hypothesis that heightened platelet reactivity and endothelial cell dysfunction are associated with acute Chagas' disease and may cause coronary microvascular spasm and/or occlusion.

Animals↗
PubMed1989

Inhibition of cyclic AMP phosphodiesterase activity of human blood platelet membrane by ADP.

Purified human blood platelet membrane showed the presence of one low Km (1.1 microM) and one high Km (5.0 microM) cyclic AMP phosphodiesterase(s). Incubation of platelet-rich plasma or gel-filtered platelets with ADP (4.0 microM), a well-known platelet aggregating agent, resulted in the inhibition of phosphodiesterase activity of the isolated membrane by 25% in 5 min at 23 degrees C. A Lineweaver-Burk plot of the enzymic activity of the membrane preparation showed that ADP specifically inhibited the low Km (1.1 microM) phosphodiesterase by reducing the Vmax from 241 to 176 pmol/mg per min with concomitant lowering of Km to 0.5 microM. In contrast, neither the high Km (5.0 microM) enzymic activity of the membrane preparation nor the phosphodiesterase activities of the cytosolic fraction of the ADP-treated platelets was affected. This effect of ADP, which was independent of platelet aggregation, reached maximal level within 5 min of incubation. When platelet-rich plasma was incubated longer in the presence of nucleotide, the inhibition of phosphodiesterase activity began to decrease, and after 20 min of incubation approx. 90% of the original enzymic activity was regained. The incubation of platelet-rich plasma with 4.0 microM ADP also increased the cyclic AMP level to twice the basal level. The effect of ADP on the phosphodiesterase activity could be demonstrated only by incubating the intact platelets with the nucleotide. The treatment of isolated membrane from platelets, previously unexposed to ADP, with the nucleotide did not inhibit the enzymic activity. The inhibition of phosphodiesterase by the nucleotide in the absence of stirring, as expected, resulted in the inhibition of platelet aggregation when these cells were subsequently stirred with 1-epinephrine or an increased concentration of ADP.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1988

Inhibition of prostaglandin E1-induced activation of adenylate cyclase in human blood platelet membrane.

Activation of human blood platelet adenylate cyclase is initiated through the binding of prostaglandin E1 to the membrane receptors. Incubation of platelet membrane with [3H]prostaglandin E1 at pH 7.5 in the presence of 5 mM MgCl2 showed that the binding of the autacoid was rapid, reversible and highly specific. The binding was linearly proportional to the activation of adenylate cyclase. Although the membrane-bound radioligand could not be removed either by GTP or its stable analogue 5'-guanylylimido diphosphate, 150 nM cyclic AMP displaced about 40% of the bound agonist from the membrane. Scatchard analyses of the binding of the prostanoid to the membrane in the presence or absence of cyclic AMP showed that the nucleotide specifically inhibited the high-affinity binding sites without affecting the low-affinity binding sites. Incubation of the membrane with 150 mM cyclic AMP and varying amounts of prostaglandin E1 (25 nM to 1.0 microM) showed that the percent removal of the membrane-bound autacoid was similar to the percent inhibition of adenylate cyclase at each concentration of the agonist. At a concentration of 25 nM prostaglandin E1, both the binding of the agonist and the activity of adenylate cyclase were maximally inhibited by 40%. With the increase of the agonist concentration in the assay mixture, the inhibitory effects of the nucleotide gradually decreased and at a concentration of 1.0 microM prostaglandin E1 the effect of the nucleotide became negligible. These results show that cyclic AMP inhibits the activation of adenylate cyclase by low concentrations of prostaglandin E1 through the inhibition of the binding of the agonist to high-affinity binding sites.

Adenylyl Cyclases↗