Intracellular calcium stores mobilized by prostaglandin E1 in vascular smooth muscle

INDAPAMIDE TREATMENT MODIFIES THE VASCULAR REACTIVITY OF NORMOTENSIVE RAT MESENTERIC ARTERIES IN VITRO LL_TTarkki!a, I. Paakkad, E. Mervaala, R. Nevala, H. Vapaatalo institute of Biomedicine, Department of Pharmacology and Toxicology, P.O. Box 8, 00014 University of Helsinki, FINLAND Indapamide is a thiazide-like, antihypertensive drug whose precise antihypertensive effect has not been clarified. The aim of this study was, using normotensive rat mesenteric artery preparations, to investigate the changes in vascular responses after in vitro and in vivo indapamide treatments. We also considered the role the endothelium in vascular responses. The in vitro pretreatment of indapamide 1-10gM did not significantly change the contractions induced by cumulatively increased concentrations of noradrenaline (NA) or potassium chloride (KCI). The acetylcholine (ACh) and sodium nitroprusside (SNP) induced relaxations were uneffected by indapamide. In vivo, one group of rats was treated with a high dose of indapamide (3mg/kg/day) and another group with a low dose of indapamide (O.3mg/kg/day). The control group received vehicle only. After seven days the vascular responses in vitro were measured. The NA and KCI induced contractions were slightly increased in the high dose group in vascular rings without endothelium. There were no significant differences between any treatment groups in vascular ring relaxations induced by ACh or SNP in the rings with or without endothelium. Our results show that indapamide administered in vitro had no effect on the vascular responses but a prolonged in vivo treatment modifies the vascular reactivity of normotensive rats in vitro. These results may be explained by the metabolite of indapamide that is formed in vivo and is more effective on vascular responses than indapamide itself•

INTRACELLULAR CALCIUM STORES MOBILIZED BY PROSTAGLANDIN E1 IN VASCULAR SMOOTH MUSCLE /

S.Zakharenkq and U•Pohl* Cardiology Research Center of Russia,Institute of Experimental Cardiology, Cherepkovskaya str. 15a,121552 Moscow,Russm; Institute of Physiology, Medical University of Luebeck, Ratzeburger Allee 180,D23538 Luebeck,Germany Objective: Since prostaglandin E 1 (PGE1) induces an increase in the intracellular free calcium concentration ([Ca2+]i) in aortic smooth muscle cells (SMC) eiher in the presence or absence of extraeellular calcium, we decided to investigate the effects of PGE 1 on different internal calcium stores. Methods: Cultured rat aortic SMC and endothelium-denuded strips of rat aorta loaded with fura2AM were used. Results: Aortic SMC reacted with a biphasic increase in [Ca2+]i to the application of a submaximal concentration of PGE 1 (10 .7 M) in a Ca 2+free solution. This effect was independent of the pretreatment with caffeine (5"10 -3 M). Ryanodine (10 -5 M) blocked an increase in [Ca2+]i produced by caffeine but failed to change the PGEl-induced rise in [Ca2+]i. Noradrenaline (NA; 10-5 M) increased [Ca2+]i in SMC in Ca2+-free solution, but after refilling of the stores and the pretreatment wi~h PGE 1 NA was ineffective. PGE 1 ~:ga~ud~C;2f+{ihaefte~dh ;_ipnrc~turee~menet Winth[N22~.t_~Utwtha: significantly smaller. Conelutsions: These results suggest that PGEl-induced calcium mobilization is independent of a depletion of caffeine-sensitive intracellular calcium stores. More likely, PGE 1 depletes IP3-sensitive stores and other ones, presumably mitochondrial.

This study was supported by the Academy of Finland.

EFECTSOF 7-NITROINDAZOLEON VASCULARNITRICOXYDESYNTHASES A. Zerrquk,M. August,P.E.Chabrierand P. Braquet.InstitutHenriBeaufourResearch Labs, 1 avenuedes Tropiques,91952LES ULIS,France. Nit• oxidesyntheses(NOS)are classifiedin two types:one is constitutive(NOSc) and locatedin vascularendotheliumand neurons,the otheris inducible(NOSi)and expressedin variouscellsafter stimulationby endotoxinsor cytokines.NOS inhibitors are used extensivelyto determinethe degree of NO involvement in biological processes.7-nitroindazole(7 NI) has beenshownto inhibitcentralNOS activityand to be devoid of effect on mean arterial pressureand on endotheliumdependent relaxation to acetylcholine (Mooreet al., 1993). The aim of this study was to characterizethe effectsof 7-NI (100 gM) on the differentvascularNOS in comparison to the non-selectiveNOS inhibitor,Nitro-L-arginine(NLA; 100 ~tM)and to the selective inhibitorof the NOSi,aminoguanidine(AG;300 gM). Experimentswire performedon intactringsof isolatedaortafromSpragueDawleyrats.The drugsweretestedfor their abilityto modifythe activityof (i) the stimulatedNOScassessedby carbachol(Cch;0.1 gM) inducedrelaxationon phenylephrine(PE, 1 gM) constrictedrings (Drugs were added before [prevention]or after [reversion]additionof Cch) (ii) the basal NOSc assessedby angiotensinII (All, 0.1 gM) inducedcontraction(Zerrouket el., 1994)(iii) theendothelialNOSiassessedby L-arginine(L-arg,300p.M)inducedrelaxationin 180 minutesincubatedringsconstrictedby PE (Zerrouket el., 1994).Our resultsshowthat, in controlringsCcheliciteda rapidrelaxation(89_.+2%).NLAcompletelypreventedand reversedthe responsesto Cch in an irreversiblemanner.7-NI reversibe]y prevented (282_4.6 % inhibition)and particularlyreversed(73+ 10 % inhibition)the Cch induced relaxation,whereasAG was totallyineffective.NLA,unlike7NI and AG, increased(25 ± 4%)the constrictorresponseto All. Additionof L-argresultedin a 38+8 % relaxation of PE constrictedrings. This effectwas fully preventedby NLA and AG, however7NI was ineffective.In conclusion,our resultsindicatethatNLAinhibitsbothstimulatedand basal NOScas well as endothelialNOSiwhereasAG is only effectiveon NOSi.7NI, ineffective on NOSi, may discriminate between stimulated and basal NOSc. Furthermore,the effect of 7NI on stimulatedNOScis morepotentwhen testedafter activationof NOScby agonist.The ineffectivenessof 7NI on basalNOScand its lack of effect on bloodpressuresuggesta predominantrole of basal NOSccomparedto stimulatedNOScin the regulationof vasculartone. Mooreetal., Br. J. Pharmacol.110:219, 1993. Zerrouket el., in Biol.NitricOxide(3) eds Moncadaet aL PortlandPress.pp 108,1994.

EFFECT OF L I T H I U M ON cAMP LEVELS IN THE P R E S E N C E OF ~-ADRENOCEPTOR ANTAGONISTS IN

RAT BRAIN. L_~Carbonell, M.L. Cuffi, F. M~rmol, J. Forn. Unitat de Farmacol0gia, Facultat de Medieina. Universitat de Barcelona. It has been reported that lithium inhibits the cAMP accumulation induced by isoprenaline and norepinephrine in brain, in a dose-dependent manner. However, this inhibitory effect of lithium was observed at lower concentrations in the presence of an o~-adrenoceptor blocker, phenoxibenzamine. The main purpose of this study was to determinate the effect of lithium in the presence of cq- or c~2-adrenergic blocking agents, in slices of rat cerebral cortex, in order to evaluated, in a more specific way, the effect of lithium on cAMP accumulation produced by catecholamines. The cAMP levels were determined by an isotopic displacement method using 3H-cA.MP and a binding protein in cortex slices. Our results showed that low lithium concentrations, starting at 0.3 x 103M, had a significant inhibitory effect on cAMP content induced by isoprenaline (1 x 104M) in brain tissue pretreated with the ~2-adrenoeeptor antagonist yohimbine (1 x 104M). On the contrary, with an % adrenoceptor antagonist such as prazosin (1 x 10-7M), the inhibitory effect of lithium on cAMP levels induced by isoprenaline, was only observed at concentrations starting at 2.5 x 103M. The results strengthen the hypothesis that the increased inhibitory activity of lithium is primarily occurring at c~2adrenoceptors.

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