Platelet prostacyclin binding in coronary artery disease.

Reduced responsiveness of platelets to prostacyclin, reported in vitro in patients with coronary artery disease, has been thought to be a factor predisposing toward coronary thrombosis and vasospasm as a result of enhanced in vivo release of cyclic endoperoxides and thromboxane A2 by the platelets. In this study, specific binding of prostacyclin to intact platelets was determined in patients with coronary artery disease by direct binding studies using 9-3H-prostacyclin sodium salt. In addition, the inhibitory effect of prostacyclin on primary aggregation induced by adenosine diphosphate and cyclic adenosine monophosphate (cyclic AMP) accumulation stimulated by prostacyclin was examined. Twenty patients with angiographically documented coronary artery disease and stable angina, 8 patients with acute myocardial infarction, 14 healthy volunteers and 10 patients with normal angiograms were studied. In patients with stable angina, binding capacity and affinity of platelet prostacyclin binding sites and prostacyclin-induced cyclic AMP accumulation were not different from those of control subjects. In patients with acute myocardial infarction, however, binding capacity of platelet prostacyclin receptors was significantly reduced (0.69 +/- 0.45 versus 1.35 +/- 0.37 pmol/10(9) platelets, p = 0.001) and the postreceptor response, represented by platelet responsiveness to prostacyclin and prostacyclin-induced cyclic AMP synthesis, was impaired. Because all patients with myocardial infarction were receiving intravenous heparin and nitroglycerin, which might interfere with platelet prostacyclin binding, competition experiments were performed in vitro. Neither heparin (3 to 250 IU/ml) nor nitroglycerin (0.8 to 22 microM) displaced specifically bound 9-3H-prostacyclin. L-Epinephrine in concentrations up to 10 microM also exhibited no competition with specific platelet prostacyclin binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Growth stimulation and chemotropic attraction of rat retinal ganglion cell axons in vitro by co-cultured optic nerves, astrocytes and astrocyte conditioned medium.

The effects of explants of optic nerves of different ontogenetic ages (P0 P14, adult), and of cultured astrocytes of various ages on the neurite regeneration of rat retinal ganglion cells (RGC) were assessed in vitro, using a three-dimensional culture system which allows the co-cultivation of various explants. Both co-cultured P0-P12 optic nerves and astrocyte cultures from P2 cerebral cortex stimulated the regeneration of neurites from the retinal explants after 3 days in culture. By contrast, P14 and older explants of the optic nerve, astrocytes from P17 optic nerve and astrocytes that had previously been grown in culture for more than 6 weeks had no effect on RGC neurite outgrowth. Moreover, both the P0-P12 optic nerve explants and the astrocytes from P2 cerebral cortex also seemed to have a chemotropic effect on the regenerating neurites, because the latter were longer on the side facing the co-explantat. The absence of a cellular bridge between retinal and optic nerve explants suggests that the effects are mediated by astroglia-derived diffusible neurite growth promoting factors. Accordingly, astrocyte-conditioned medium from P2 astrocytes also stimulated the outgrowth of neurites from the retinal explants. These findings show that immature astrocytes of a limited ontogenetic period release as yet unknown diffusible neurite growth-promoting factors which stimulate the regeneration of neurites from retinal explants.

Platelet prostacyclin binding in smokers.

Binding capacity (Bmax) and dissociation constant (KD) of platelet prostacyclin (PGI2) receptors in 23 male smokers and 14 nonsmokers have been determined by direct binding studies to investigate whether platelet prostacyclin binding is altered in smokers. In addition, the inhibitory effect of PGI2 (IC50) on adenosine diphosphate (ADP)-induced platelet aggregation was measured. As confirmed by discriminant analysis, 69% of the smokers had significantly different Bmax and KD. Binding capacity was increased in 12 smokers (Bmax + 74%), with a concomitant decrease in affinity (KD + 94%). In these volunteers, the postreceptor responses (PGI2-induced cyclic adenosine monophosphate [AMP] accumulation in platelet-rich plasma as well as IC50) did not differ from those of controls. In contrast, four smokers with considerably reduced PGI2 binding capacity (Bmax - 65%) exhibited a lower antiaggregatory effect (IC50 + 74%), although the affinity was slightly increased (KD - 61%). Nicotine, L-epinephrine, and prostaglandin E2 did not significantly compete with the binding of 9-3H-PGI2 sodium salt. The antiaggregatory effect of PGI2 on ADP-induced platelet aggregation, however, was inhibited by L-epinephrine (Ki 26 nmol/L) and prostaglandin E2 (Ki 230 nmol/L). Our data suggest that with respect to platelet PGI2 binding and in vitro responsiveness to PGI2, smokers are a heterogeneous population. Although increased binding capacity was observed in 50% of the smokers investigated, our data provide no evidence that a biologically relevant upregulation, for example with concomitant enhanced postreceptor reaction, occurs in smokers.