Background and purpose:  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. Experimental approach:  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. Key results:  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. Conclusions and implications:  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.

The effect of thapsigargin (TG) and cyclopiazonic acid (CPA) on the mechanical activity of the rat pulmonary artery were investigated. In chemically (beta-escin)-skinned arterial strips, application of TG (0.1-1 microM) or CPA (0.5-10 microM) prior and throughout the loading procedure of the internal Ca2+ stores (0.3 microM free Ca2+ ions for 8-10 min) concentration dependently inhibited the subsequent contractile response induced by noradrenaline (NA, 10 microM) or caffeine (25 mM). In intact strips repeatedly incubated in a Ca(2+)-containing solution (2.5 mM for 10 min), followed by incubation in a Ca(2+)-free solution 12 min before NA-stimulation, TG and CPA not only inhibited the NA-induced contraction but also increased the tension which appeared during the exposure time to Ca2+. The two phenomena developed with similar time courses. The increase in tension during the readmission of Ca2+ ions was not antagonized by verapamil (10 microM) or nifedipine (1 microM) but was blocked by La3+ (50 microM) and Co2+ (1 mM) ions. The amplitude of the verapamil-insensitive TG (or CPA)-induced contraction was dependent on the external [Ca2+] [0.1-10 mM, concentration for half maximal effect (EC50) = 0.85 mM], not modified by the reduction of the external [Na+] (from 130 to 10 mM) and decreased by depolarization of the strip using K(+)-rich (30-120 mM) solutions. Under the latter condition, 38 +/- 9 and 83 +/- 4% reduction (n = 5) was observed in the presence of 60 and 120 mM K+ respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

The effect of angiotensin II (ANG II) on the cytosolic calcium concentration ([Ca2+]i) was studied in freshly (2-8 h) isolated myocytes from the main pulmonary artery of the rat. Myocytes were loaded with the fluorescent indicator indo 1 (1 microM for 30 min) and experiments were performed at room temperature. Short (30 s) applications of ANG II (0.01-10 microM) induced cyclic variations oscillations in [Ca2+]i. The ANG II-induced response was typically composed of three to six oscillations of constant duration (9.8 +/- 0.5 s, n = 40) but of decreasing amplitude. The first oscillation increased [Ca2+]i from 119 +/- 4 to 884 +/- 33 nM (n = 32). ANG II-induced response was concentration dependently inhibited by previous addition to the bathing solution of losartan or SR-47436 (0.01-0.1 microM, each), two specific AT1 receptor-antagonists. In Ca(2+)-free external solutions (containing 0.4-1 mM EGTA), ANG II still produced oscillation in [Ca2+]i. These oscillations disappeared in myocytes pretreated with neomycin (0.1 microM), thapsigargin (1 microM), or phorbol 12,13-dibutyrate (PDBu, 1 microM). In contrast to ANG II, caffeine (o.5-10 mM) induced only one transient rise in [Ca2+]i, which was unaltered by neomycin or PDBu but blocked by thapsigargin. These results show that ANG II produces oscillations in [Ca2+]i in pulmonary arterial myocytes via stimulation of AT1 receptors coupled to phospholipase C activation. ANG II-induced oscillations appear to be related to the cycling of Ca2+ ions from an intracellular store (presumably the sarcoplasmic reticulum) by a primarily inositol trisphosphate-dependent Ca2+ release.