Differential effects of various vasoactive drugs on basal and stimulated levels of TXB2 and 6-keto-PGF1 alpha in rat brain

Brain fixation for analysis of brain lipid-mediators of signal transduction and brain eicosanoids requires head-focused microwave irradiation: an historical perspective

To microwave or not to microwave, that is the question that has confounded the neurochemist as the quest for reducing changes in neurochemicals associated with post-mortem delay has evolved over the years. Rapid changes in brain constituents during the post-mortem delay have been recognized for years as a problem. What is real and what is artifact? What are true basal levels of molecules found in the brain? In the 1920s, neurochemists recognized this issue and determined freezing of the brain was most advantageous for halting rapid breakdown of some molecules and rapid formation of others. By the early 1970s, a number of laboratories noted that freezing the brain in situ or upon removing it from the cranial vault was not sufficient to reduce alterations in brain chemistry. Groups began experimenting with two different techniques to attack this problem, freeze-blowing and head-focused microwave irradiation. My laboratory and others have found that the utilization of head-focused microwave irradiation to halt enzymic alterations in lipids is an essential tool to limit alterations post-mortem. Recently, we and others have demonstrated that this technique is essential in reliably assessing brain eicosanoid levels, without such fixation true basal levels of eicosanoids are impossible to determine and the high concentrations seen in some paradigms may be merely an artifact produced during handling of the brain. Thus, for eicosanoid analysis and other applications in measuring brain lipid levels, head-focused microwave irradiation is an essential tool for the lipid neurochemist.

Formation of eicosanoids, E2/D2 isoprostanes, and docosanoids following decapitation-induced ischemia, measured in high-energy-microwaved rat brain

Inflammatory lipid mediators derived from arachidonic acid (AA) and docosahexaenoic acid (DHA) modify the pathophysiology of brain ischemia. The goal of this work was to investigate the formation of eicosanoids and docosanoids generated from AA and DHA, respectively, during no-flow cerebral ischemia. Rats were subjected to head-focused microwave irradiation 5 min following decapitation (complete ischemia) or prior to decapitation (controls). Brain lipids were extracted and analyzed by reverse-phase liquid chromatography-tandem mass spectrometry. After complete ischemia, brain AA, DHA, and docosapentaenoic acid concentrations increased 18-, 5- and 4-fold compared with controls, respectively. Prostaglandin E(2) (PGE(2)) and PGD(2) could not be detected in control microwaved rat brain, suggesting little endogenous PGE(2)/D(2) production in the brain in the absence of experimental manipulation. Concentrations of thromboxane B(2), E(2)/D(2)-isoprostanes, 5-hydroxyeicosatetraenoic acid (5-HETE), 5-oxo-eicosatetraenoic acid, and 12-HETE were significantly elevated in ischemic brains. In addition, DHA products such as mono-, di- and trihydroxy-DHA were detected in control and ischemic brains. Monohydroxy-DHA, identified as 17-hydroxy-DHA and thought to be the immediate precursor of neuroprotectin D(1), was 6.5-fold higher in ischemic than in control brain. The present study demonstrated increased formation of eicosanoids, E(2)/D(2)-IsoPs, and docosanoids following cerebral ischemia. A balance of these lipid mediators may mediate immediate events of ischemic injury and recovery.

The carbochromene derivative AD6 reduces the TxB2/6-keto-PGF1 alpha ratio in cerebral cortex during hypoxia and recovery and leukotriene synthesis in brain tissue, in the rat

Pretreatments of rats with the Carbochromene derivative AD6 (4 mg/kg i.p., 2 h before sacrifice) resulted in elevation of brain levels of 6-keto-PGF1 alpha in cerebral cortex under physiological conditions, had no effect on levels of TxB2 and 6-Keto-PGF1 alpha at 30 min of hypoxia (respiration of 5% O2 in N2) and prevented the accumulation of TxB2 occurring in brain at 5 min of recovery after hypoxia. In addition, the accumulation of LTC4 and B4 in brain slices incubated in the presence of the Ca++ ionophore A23187 and arachidonic acid, was reduced in samples obtained from pretreated rats. The drug, thus, had favourable effects on the 6-keto-PGF1 alpha/TxB2 ratio in normal conditions, as well as in conditions of altered oxygen supply. In addition it reduced the formation of compounds, the leukotrienes, which may exert pro-inflammatory activities on the cerebral microcirculation.

The increase of the openings of the surface-connected canalicular system in weakly stimulated platelets is prevented by a carbochromen derivative. A computerized morphometric analysis of freeze-etched human platelet plasma-membrane

When thrombin is added to platelet rich plasma at very low concentrations (0.02 U/ml), platelets undergo an activation process. Under these conditions platelets discharge beta-thromboglobulin, platelet factor 4 and the "platelet derived growth factor". In this paper we present evidence that when human platelets are weakly stimulated with thrombin, the number of openings of the surface connected canalicular system (SCCS) increases. This was observed ultrastructurally by the freeze-etching technique. 8-chlorocarbochromen, an antiaggregating drug, seems to inhibit this increase.

Action of AD6 (8-monochloro-3-beta-diethylaminoethyl-4-methyl-7-ethoxycarbonylmet hox y coumarin) on human platelets in vitro

The action of AD6 was tested in vitro on human platelets by measuring beta-thromboglobulin (BTG), platelet factor 4 (PF4) and thromboxane B2 (TXB2) release as well as aggregation. BTG and PF4 release from blood anticoagulated with sodium citrate was inhibited by AD6 during a 3 h incubation. Platelet rich plasma (PRP) was stimulated with ADP, collagen, sodium arachidonate, PAF, A23187 and epinephrine, while resuspended washed platelets (WP) were stimulated by thrombin. AD6 (5-100 microM) inhibited dose dependently aggregation, BTG, PF4 and TXB2 release induced by threshold concentration of all the tested aggregating agents; however AD6 action could be overcome by increasing the concentration of the stimulating agents. After cyclo-oxygenase blockade by acetylsalicylic acid (ASA), PRP was stimulated by a supramaximal concentration of PAF. Under these circumstances we could observe a reversible aggregation and a partial release of BTG and PF4, AD6 was able to further reduce aggregation and release. Cyclic AMP accumulation induced in WP by prostacyclin was not modified by AD6 (100 microM), while theophylline greatly potentiated prostacyclin action. We conclude that AD6 is an inhibitor of platelet activation in vitro. Its mode of action is different from cyclo-oxygenase blockade and provides inhibition of platelet activation by a number of different stimuli.