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Pulmonary arterial hypertension (PAH) is associated with increased contraction and proliferation of pulmonary vascular smooth muscle cells. The anti-diabetic drug metformin has been shown to have relaxant and anti-proliferation properties. We thus examined the effect of metformin in PAH.Metformin effects were analysed in hypoxia- and monocrotaline-induced PAH in rats. Ex vivo and in vitro analyses were performed in lungs, pulmonary artery rings and cells.In hypoxia- and monocrotaline-induced PAH, the changes in mean pulmonary arterial pressure and right heart hypertrophy were nearly normalized by metformin treatment (100 mg.kg(-1).day(-1)). Pulmonary arterial remodelling occurring in both experimental models of PAH was also inhibited by metformin treatment. In rats with monocrotaline-induced PAH, treatment with metformin significantly increased survival. Metformin increased endothelial nitric oxide synthase phosphorylation and decreased Rho kinase activity in pulmonary artery from rats with PAH. These effects are associated with an improvement of carbachol-induced relaxation and reduction of phenylephrine-induced contraction of pulmonary artery. In addition, metformin inhibited mitogen-activated protein kinase activation and strongly reduced pulmonary arterial cell proliferation during PAH. In vitro, metformin directly inhibited pulmonary artery smooth muscle cell growth.Metformin protected against PAH, regardless of the initiating stimulus. This protective effect may be related to its anti-remodelling property involving improvement of endothelial function, vasodilatory and anti-proliferative actions. As metformin is currently prescribed to treat diabetic patients, assessment of its use as a therapy against PAH in humans should be easier.

As the cellular and molecular mechanisms of major arterial diseases such as atherosclerosis and hypertension are being more clearly defined, it is becoming apparent that these pathological processes share a number of functional and biochemical features in the vessel wall. Typically, arterial diseases are associated with functional and structural wall alterations including modified contractile properties, smooth muscle cell hypertrophy and proliferation, endothelial dysfunction, excessive extracellular matrix accumulation and inflammation. Small G proteins of the Rho family are defined as major regulators of cell functions including migration, proliferation, differentiation and gene transcription. Recent studies have demonstrated that activation of Rho proteins appears to be a common component for the pathogenesis of hypertension and vascular proliferative disorders. Functional analyses have further revealed that RhoA-dependent pathways are involved in excessive contraction, migration and proliferation associated with arterial diseases. This review focuses on the role of Rho proteins, in particular RhoA, in vascular smooth muscle cells and the involvement of Rho-dependent signaling pathways in vascular diseases.

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The occurrence of a late reaction following exercise induced asthma is questionable and its relationship with the non specific bronchial hyperreactivity is poorly known. In this study, nine patients (age 15-21 years) underwent an exercise challenge in order to (a) determine the incidence of immediate and late phase reaction and (b) analyse the modifications of non specific bronchial hyperreactivity. Study design was a follow; day-3: determination of bronchial responsiveness to metacholine; day 0: control day with FEV1 measurements every hour for 11 hours; day 1: exercise challenge followed by a careful observation of change in FEV1; day 2: new determination of bronchial responsiveness to metacholine. An immediate exercise induced bronchial obstruction was observed in 5 patients. A late phase reaction (6th hour) with a fall of FEV1 equal to or more than 20% has been demonstrated in two patients. For the former, the change in FEV1 did not differ from the value of the control day. For the second, the FEV1 changed spontaneously during the control day so that decreases of FEV1 during control and challenge days were parallel. Thus, no late phase reaction were observed (F = 0.46; ns). There was no modification of bronchial responsiveness to metacholine (pre-exercise: 1,784 +/- 1,970 [SD]; post-exercise 1,827 +/- 2,231 micrograms [SD]). The lack of true late phase reaction when the post-exercise change in FEV1 is compared to the one of a control day and the absence of modification of non specific bronchial hyperreactivity weaken the hypothesis of an inflammatory mechanism of exercise induced asthma.

A rapid transient rise in the free cytosolic Ca2+ concentration is one of the earliest events in smooth muscle cell activation and is involved in the opening of several classes of Ca2(+)-sensitive ion channels such as K+ channels and Cl- channels. In portal vein smooth muscle cells, in addition to the Ca(2+)-dependent Cl-current, single-channel activities were recorded in response to external application of 10 mM caffeine, in the absence of EGTA in the pipette solution. The conductance of this novel type of channel was around 200 pS for membrane potentials ranging between -100 to +60 mV. The single-channel activities were also induced by external application of noradrenaline (10(-5) M) or acetylcholine (10(-5) M), by Ca2+ entry through voltage-dependent Ca(2+)-channels, and by intracellular application of ryanodine (10(-5) M). The caffeine-activated single-channel currents disappeared when 10 mM EGTA were added to the pipette solution or after replacement of external Ca2+ with Ba2+. These results show that these channels are Ca(2+)-dependent. Alteration of the Cl- equilibrium potential did not produce any change in the reversal potential of the caffeine-activated single-channel current, indicating that it was not carried by Cl- ions. The value of the reversal potential was about + 10 mV, irrespective of the CsCl-, KCl- or NaCl-containing solutions used to fill the pipette. Caffeine activated single-channel currents when cells were bathed in 90 mM Ba2+ plus 1 mM Ca(2+)- or 91 mM Ca(2+)-containing solutions, showing that divalent cations permeate the channels.(ABSTRACT TRUNCATED AT 250 WORDS)

The contractile effect of okadaic acid (OA) and its derivatives was investigated in the rat uterus. OA (20 microM) induced a transient contraction which, after plateauing, slowly decreased. The structurally related compound okadanol (20 microM) failed to induce any significant contraction. Conversely, the synthetic compound methyl okadaate (20 microM) and the naturally occurring ester 7'-hydroxy-4'-methyl-2'-methylen-hept-4'(E)-enyl okadaate (20 microM) were as active as the free acid. The OA-induced contraction was unaffected in the presence of neomycin (5 mM), mepacrine (30 microM), 1-[N,O-bis(1,5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-phenylpiperaz ine (10 microM), calphostin C (3 microM) and 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (30 microM). The calmodulin inhibitor N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide hydrochloride (100 microM) did not modify the amplitude of the OA-induced contraction but significantly increased the rate of tension decay. The myosin light chain kinase inhibitor 1-(5-chloronaphthalene-1-sulfonyl)-1H-hexahydro-1,4-diazepine hydrochloride (1 mM) significantly reduced the peak amplitude of the contraction. Staurosporine (0.03-0.1 microM) did not modify the contractile component of the OA-induced response but inhibited the subsequent decrease in tension. In freshly dispersed myometral cells loaded with the fluorescent Ca++ indicator indo 1, OA did not produce any significant increase in [Ca++]i. OA (5- to 90-min contact) also failed to modify the intracellular levels of arachidonic acid, compared with basal values. These data suggest that in the rat uterus 1) the contractile effect of OA (20 microM) is specifically mediated by inhibition of protein phosphatases type 1 and/or 2A and is related to a direct interaction with the contractile machinery; 2) the decreasing phase of the OA-induced mechanical response could be mediated by a staurosporine-sensitive protein kinase different from protein kinase C.