bq-123 and Epilepsy

Endothelin-1 (ET) has been shown to be involved in human pathological conditions, but its physiological function remains to be elucidated. The aim of this work was to assess whether endothelium-derived ET was involved in the overall responsiveness of freshly isolated human pial arteries.. Samples of cerebral cortex, otherwise discarded, were obtained during tumor or epileptic lesion resections (n = 10 donors). Arterial segments were isolated and mounted on a microvessel myograph.. Inhibition of nitric oxide (NO) formation with N omega-nitro-L-arginine (L-NA, 100 micromol/L) increased basal tone by 7+/-1% Emax (n=5). This increase in tone was fully abolished in the presence of BQ123 (1 micromol/L; ET(A) receptor antagonist, P<.05) but potentiated by a subthreshold concentration of exogenous ET (1 nmol/L; 33+/-8% Emax; P<.05). In the presence of L-NA, serotonin (10 micromol/L)-induced tone was doubled compared with the control response (P<.05) but reduced by 90% in the presence of BQ123 (P<.05). In the absence of L-NA, BQ123 prevented serotonin-induced tone (n=3). Oxymetazoline, a selective alpha2-adrenergic receptor agonist, induced an endothelium-dependent relaxation of preconstricted human pial arteries. The relaxation was partially sensitive to NO synthase inhibition and fully prevented by the addition of ET, whereas substance P-induced relaxation was preserved. Glibenclamide (1 micromol/L), an inhibitor of ATP-sensitive K+ channels and tetraethylammonium (1 mmol/L), an inhibitor of Ca2+-activated K+ channels had no effect on oxymetazoline-induced relaxation.. The results of this study suggest first that ET is involved in the tonic response induced by NO synthase inhibition; second, part of the contractile response induced by serotonin is endothelium-dependent and sensitive to BQ123; and third, the data suggest that activation of alpha2-adrenergic receptors generated an endothelium-dependent relaxation that was selectively inhibited by exogenous ET.

Topics: Adolescent; Adrenergic alpha-Agonists; Adult; Arteries; Brain Neoplasms; Cerebral Cortex; Endothelin Receptor Antagonists; Endothelin-1; Endothelium, Vascular; Enzyme Inhibitors; Epilepsy; Female; Glyburide; Humans; Hypoglycemic Agents; Male; Middle Aged; NG-Nitroarginine Methyl Ester; Nitric Oxide; Nitric Oxide Synthase; Oxymetazoline; Peptides, Cyclic; Pia Mater; Potassium Channel Blockers; Serotonin; Substance P; Tetraethylammonium; Vasoconstrictor Agents; Vasodilator Agents

The vasoactive peptide, endothelin-1 (ET-1) has been implicated in the pathophysiology of various diseases. Recently, we have shown that human brain endothelial cells both secrete and express immunoreactive ET-1 high-affinity ETA receptors coupled to activation of phospholipase C (PLC). The present study demonstrates concentration-dependent stimulation of prostanoids [thromboxane B2 (TxB2), prostaglandin F2 alpha (PGF2 alpha), 6-keto prostaglandin F1 alpha (6-keto PGF1 alpha) prostaglandin E2 (PGE2), and prostaglandin D2 (PGD2)] production by ET-1 in capillary endothelial cells derived from human brain (HBCEC). The increase in the vasoconstrictive prostanoids TxA2 and PGF2 alpha temporally preceded that of the vasodilatory PGI2, PGE2 and PGD2, and was seen after 15 min of incubation with ET-1 (10 nM). Increased production of vasodilatory prostanoids was observed between 4-8 h of incubation, whereas normalization of both vasoconstrictive and vasodilatory prostaglandins occurred 24 h after addition of ET-1. Both ET-1-stimulated prostanoid and IP3 production were inhibited by BQ123, a specific antagonist of ETA receptors. ET-1-induced prostanoid secretion by HBCEC was also inhibited by dexamethasone (50 microM) and diminished by neomycin (50 microM) and verapamil (10 microM) but not by nifedipine. Phorbol myristate ester potentiated ET-1-stimulated prostanoid secretion, whereas it inhibited IP3 production. Data indicate that ET-1 activates phospholipase A2 (PLA2) and PLC in HBCEC by different intracellular mechanisms. The subsequently induced secretion of vasoactive prostanoids by HBCEC may contribute both qualitatively and temporally to the vasoactive actions of ET-1.

Topics: Analysis of Variance; Capillaries; Cell Line; Dexamethasone; Endothelin Receptor Antagonists; Endothelins; Endothelium, Vascular; Epilepsy; Humans; Inositol; Kinetics; Neomycin; Peptides, Cyclic; Prostaglandins; Temporal Lobe; Tetradecanoylphorbol Acetate; Verapamil