Z. Jerushalmy

Effect of melatonin on active transport of serotonin into blood platelets

Previous research has demonstrated that the circadian rhythm of melatonin negatively correlates with that of the sensitivity of platelet serotonin uptake sites. Moreover, serotonin has been found to be a competitive inhibitor of melatonin binding to platelets. The goal of the present study was to investigate whether melatonin directly affects platelet serotonin transport. Blood samples from 12 healthy subjects were assayed for both serotonin transport into platelets. Active transport of serotonin (at a concentration of 10(-6) M) into blood platelets was measured in the presence of melatonin at physiological concentrations (10(-12) M to 2 x 10(-9) M) and high nonphysiological concentrations (2 x 10(-8) M to 2 x 10(-3) M). Melatonin inhibited serotonin uptake by blood platelets at the high concentrations only ( > 10(-5) M with IC50 value of 1.1 x 10(-3) M) and had no effect at physiological concentrations.

Lack of association between cholesterol blood levels and platelet serotonin uptake

It has been suggested that low serum cholesterol interferes with brain serotonergic functioning, which results in increased suicidal and aggressive tendencies. To test this hypothesis we investigated the relationship between serum cholesterol, high-density lipoprotein (HDL), low-density lipoprotein (LDL) and triglyceride levels, and serotonin uptake by blood platelets in 17 healthy men aged 39.5 +/- 10.2 years. Platelet serotonin uptake and serum lipids were assayed concomitantly for each individual. Serum cholesterol levels and other serum lipid levels did not correlate with serotonin uptake by platelets at the concentration of 2 x 10(-5) M (a concentration within the maximal uptake capacity range). The results indicate no influence of cholesterol on serotonin uptake, as opposed to some investigators who suggested that high risk of suicide and aggressiveness in hypocholesterolemic individuals is related to impaired serotonin transport.

Effect of Echis coloratus venom on brain vessels

Abstract The effect of Echis coloratus venom on the brain capillaries of the mouse was studied electron-microscopically using horseradish peroxidase as a tracer. The envenomation resulted in breakdown of the blood-brain barrier manifested by leakage of the peroxidase through the capillary wall. The peroxidase penetrated both by endothelial pinocytosis and through opened tight junctions between the endothelial cells. The envenomated mice showed hemorrhages and intravascular fibrin clots in the lungs and kidneys but not in the brain.

Alteration of Rat Bone Marrow Megakaryocytes Following Administration of Cytosine Arabinoside, Daunomycin and Hydroxyurea

The in vivo effects of three cytotoxic agents--cytosine arabinoside, daunomycin and hydroxyurea on rat bone marrow megakaryocytes were studied, specifically the relative count, the type percentage and the morphology. All three agents caused thrombo-cytopenia, a decrease in the number of megakaryocytes relative to the nucleated bone marrow cells, and a decrease in the percentage of megakaryoblasts, associated with an increase in the percentage of granular megakaryocytes. A decreased lobulation of the megakaryocytes was observed following the administration of cytosine arabinoside and of daunomycin. Thrombosthenin, examined immunologically, remained detectable in the bone marrow smears throughout the various stages of megakaryocyte alteration.

Enzymes of Purine Metabolism in Platelets: Phosphoribosylpyrophosphate Synthetase and Purine Phosphoribosyltransferases

Human platelets do not synthesize nucleotides de novo (1) but have been demonstrated to possess salvage pathways utilizing adenine and adenosine (2,3). On the other hand, no evidence has been reported as yet for the presence of hypoxanthine-guanine phosphoribosyltransfe-rase (HGPRT) in human platelets.

Phosphoribosylpyrophosphate Synthetase and Purine Phosphoribosyltransferases in Human and Rabbit Blood Platelets

Phosphoribosylpyrophosphate synthetase and hypoxanthine-guanine phosphoribosyltransferase (HGPRT) activities were demonstrated in human and rabbit platelet lysates. Comparative measurement of HGPRT ac

De novo Synthesis of Purine Nucleotides in Human Blood Platelets

Human blood platelets were found to carry the complete pathway of de novo purine nucleotide synthesis. The rate of purine synthesis was gauged by the rate of incorporation of precursor (14C)formate into purines. The effect on formate incorporation of several compounds known to inhibit purine synthesis de novo was studied. Adenine, orotic acid and azaserine inhibited purine synthesis, but hypoxanthine and allopurinol did not. Platelet content of phosphoribosylpyrophosphate (PRPP) and of ribose-5-pes. Incubation of intact platelets with high inorganic phosphate concentrations caused an increase in platelet PRPP content but did not affect R-5-P content or the rate of purine synthesis de novo.