Effects of ONO-3708, an antagonist of the thromboxane A2/prostaglandin endoperoxide receptor, on blood vessels

Antagonistic Effects ofGingko bilobaandSophora japonicaon Cerebral Vasoconstriction in Response to Histamine, 5-Hydroxytryptamine, U46619 and Bradykinin

The aim of this study was to evaluate, for the first time, the antagonistic effects of Gingko biloba leaf (GB) and Sophora japonica L. flower bud (SJ) extracts on cerebral vasoconstriction in response to KCl, extracellular Ca[Formula: see text], histamine, 5-hydroxytryptamine (5-HT), 9,11-dideoxy-9[Formula: see text],11[Formula: see text]-methanoepoxy prostaglandin (PG) F[Formula: see text](U46619) and bradykinin (BK), in order to explain their traditional application for diseases associated with cerebral vasospasm. Isolated porcine basilar arteries (PBA) and endothelial cells from them were used as the study materials. Neither SJ nor GB had any effect on the contractions induced by KCl and extracellular Ca[Formula: see text]. SJ significantly inhibited the contraction induced by histamine, 5-HT, U46619 and BK, whereas GB inhibited histamine-induced contraction, but had no effects on the contractions induced by 5-HT, U46619 and BK. In the presence of diphenhydramine (a H1receptor antagonist), ketanserin (a 5-HT2receptor antagonist) and ONO-3708 (a thromboxane (TX) A2/PG receptor antagonist), the inhibitory effects of these extracts on the contractions induced by histamine, 5-HT and U46619 were abolished. SJ significantly inhibited the contractions induced by BK and PGF[Formula: see text], but in the presence of ONO-3708 (10[Formula: see text] M) had no effect on them. BK enhanced the production of PGF[Formula: see text] from cultured PBA endothelium cells, and SJ significantly attenuated this enhancement. These results suggest that SJ and GB have a H1-antagonistic effect, and that SJ also attenuates cerebral vasoconstriction mediated via 5-HT2and TXA2/PG receptors. These findings appear to explain why SJ has been used traditionally as a therapeutic medication for cerebral vasospasm after cerebral hemorrhage.

Effect of phospholipase C blockade on cerebral vasospasm

BACKGROUND

Delayed cerebral ischemia due to cerebral vasospasm remains a major cause of morbidity and mortality following subarachnoid hemorrhage. Oxyhemoglobin (OxyHb) and vasoconstrictor prostanoids have been suggested as putative spasmogens. We have previously reported a synergistic vasoconstrictive action between thromboxane A(2) (TXA(2)) and OxyHb. In the present study we examine the effect of neomycin, a phospholipase C inhibitor, on the cerebral vasoconstriction induced by TXA(2) and OxyHb.

METHODS

Using an in vitro tissue bath method, we assess the effect of neomycin in a concentration-dependent manner, on isolated porcine basilar arteries constricted by U-46619 (TXA(2) analogue) and OxyHb.

RESULTS

The functional synergism between TXA(2) and OxyHb, leading to significant cerebral vasoconstriction, is attenuated in a dose-dependent manner by neomycin.

CONCLUSION

Blockade of phospholipase C may provide an alternative strategy in the treatment of subarachnoid-hemorrhage-induced cerebral vasospasm.

Thromboxane A2, released by the anti-tumour drug irinotecan, is a novel stimulator of Cl- secretion in isolated rat colon

1. A camptothecin derivative, irinotecan (Cpt-11), is a topoisomerase I inhibitor and has a strong activity against a broad range of human cancer. One of the side-effects of this drug is diarrhoea. Here, we tried to determine the mediator of the irinotecan-induced Cl- secretion which may underlie this diarrhoea, using isolated mucosae of rat distal colon. 2. Irinotecan increased Cl- secretory current in a concentration-dependent manner across the mucosa, set between Ussing chambers. Thromboxane A2 (TXA2) has not been reported to date as a physiological stimulant of Cl- secretion in the distal colon. However, the major part of the present irinotecan-induced current was inhibited by selective thromboxane A2 receptor antagonists (KW-3635 and ONO-3708), and a selective thromboxane synthase inhibitor (Y-20811). In fact, we found that irinotecan stimulated the release of TXA2 in a concentration-dependent manner from the isolated mucosa into the bathing solutions. 3. Furthermore, 9,11-epithio-11,12-methano-thromboxane A2 (STA2), a stable analogue of TXA2, induced Cl- secretion, which was almost completely inhibited by the TXA2 receptor antagonists. 4. In single cells of isolated crypts, STA2 depolarized the cell and increased the membrane conductance, indicating that STA2 opened the apical Cl- channel of the crypt cells. 5. We conclude, therefore, that the irinotecan-induced endogenous TXA2 is a novel stimulant of the Cl- secretion from the crypt cells of distal colon.

A rapid and simple method for measuring thymocyte apoptosis by propidium iodide staining and flow cytometry

Corticosteroids, calcium ionophores and anti-CD3 monoclonal antibodies kill mouse thymocytes incubated in vitro. Cell death is preceded by extensive DNA fragmentation into oligonucleosomal subunits. This type of cell death (apoptosis), which physiologically occurs in the intrathymic process of immune cell selection, is usually evaluated by either electrophoretic or colorimetric methods which measure DNA fragmentation in the nuclear extracts. These techniques are unable to determine the percentage of apoptotic nuclei or recognize the apoptotic cells in a heterogeneous cell population. We have developed a flow cytometric method for measuring the percentage of apoptotic nuclei after propidium iodide staining in hypotonic buffer and have compared it with the classical colorimetric and electrophoretic techniques using dexamethasone (DEX)-treated mouse thymocytes. Apoptotic nuclei appeared as a broad hypodiploid DNA peak which was easily discriminable from the narrow peak of thymocytes with normal (diploid) DNA content in the red fluorescence channels. When the DEX-induced apoptosis was inhibited by either low-temperature (4 degrees C) incubation or cycloheximide treatment, no hypodiploid DNA peak appeared. Similarly, thymocyte death induced by sodium azide, a substance with cell-killing activity through non-apoptotic mechanisms, did not result in any variation in the normal DNA peak. The flow cytometric data showed an excellent correlation with the results obtained with both electrophoretic and colorimetric methods. This new rapid, simple and reproducible method should prove useful for assessing apoptosis of specific cell populations in heterogeneous tissues such as bone marrow, thymus and lymph nodes.