Cardiovascular Pharmacology PKG is involved in testosterone-induced vasorelaxation of human umbilical artery Elisa Cairrão a,b , António José Santos-Silva a , Ignacio Verde a, ⁎ a CICS — Centro de Investigação em Ciências da Saúde, Universidade da Beira Interior, Av. Infante D. Henrique, 6200-506 Covilhã, Portugal b Centro Hospitalar da Cova da Beira E.P.E. Quinta do Alvito, 6200-251 Covilhã, Portugal abstract article info Article history: Received 25 November 2009 Received in revised form 3 March 2010 Accepted 19 April 2010 Available online 2 May 2010 Keywords: Human umbilical artery Testosterone PKG ANP Potassium channel Vasorelaxation The cyclic nucleotides involvement in the vasorelaxation induced by testosterone in human umbilical artery was investigated. The effect of this hormone on denuded human umbilical arteries contracted by serotonin (5-HT), histamine or KCl was analysed. Testosterone effect on potassium current (I K ) was also studied in human umbilical artery vascular smooth muscle cells (HUASMC). In general, the relaxant effects of testosterone, sodium nitroprusside (SNP) and atrial natriuretic peptide (ANP) are similar. The testosterone relaxant effect is not different to the induced by the conjoint application of ANP and testosterone. However, the effects of SNP and testosterone seem additive. The inhibition of protein kinase A (PKA) did not modify the testosterone relaxant effect, but protein kinase G (PKG) inhibition significantly reduced the testosterone effect independently of the contractile stimuli. In HUASMC, the I K is mainly constituted by potassium exit through voltage sensitive (K V ) and large-conductance Ca 2+ activated (BK Ca ) potassium channels. Testosterone significantly activates the basal I K . SNP does not induce a significant modification in basal or testosterone stimulated I K . In contrast, ANP stimulates the basal I K , but does not increase the testosterone stimulation on I K . The I K increases induced by testosterone or by ANP are not significantly affected by the PKA inhibition, but are completely inhibited by the PKG inhibition. Our results show that testosterone and ANP stimulate the activity of BK Ca and K V channels due to PKG activation and suggest that this hormone relaxes by activating particulate guanylate cyclase which increases the cGMP intracellular level. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Since the umbilical blood vessels are not innervated, the human umbilical artery tonus is modulated by endocrine and paracrine mechanisms that regulate the contractile state of smooth muscle cells. This regulation is extremely important for optimum gas and nutrient exchange between the foetus and the placenta. During pregnancy, there is an increase in the amounts of some circulating sex steroid hormones, such as androgens, which show a higher concentration in the umbilical artery than in the umbilical vein, indicating that these androgens are produced mainly in the foetal compartment and can have a main role in this vessels (Pasqualini, 2005). Studies performed in the last years have demonstrated that testosterone acts as direct vasodilator (Cairrao et al., 2008; Malkin et al., 2006; Yildiz et al., 2005). Despite of this action, some authors suggested that high levels in maternal serum of androgen concentration during pregnancy are associated with preeclampsia (Salamalekis et al., 2006) and pregnan- cy-induced hypertension (Gerulewicz-Vannini et al., 2006). To explain some of the rapid non-genomic actions of testosterone, the involvement of several signalling pathways has been proposed. The inhibition of voltage-dependent calcium channels and/or recep- tor-operated calcium channels by testosterone in different arteries was suggested (Jones et al., 2002; Murphy and Khalil, 1999; Perusquia and Villalon, 1999). In contrast, other authors showed that in some arteries testosterone induces vasorelaxant effect due to activation of potassium channels, such as ATP-sensitive potassium channels (K ATP ) (Chou et al., 1996; Honda et al., 1999), voltage sensitive potassium channels (K V )(Cairrao et al., 2008; Ding and Stallone, 2001; Yue et al., 1995), and large-conductance Ca 2+ activated potassium channels (BK Ca ) (Cairrao et al., 2008; Yildiz et al., 2005). Furthermore, Deenadayalu et al. (2001) {#2916} suggested that the activation of BK Ca channels by testosterone could be associated with increase in the intracellular levels of cGMP. The NO donors and the atrial natriuretic peptide (ANP) are potent vasodilators that act by increasing intracellular cGMP, resulting in protein kinase G (PKG) activation (Bialecki and Stinsonfisher, 1995; Francis and Corbin, 1994; Landgraf et al., 1992; Tanaka et al., 1998). Recent studies have demonstrated that cGMP produced by guanylate cyclase (GC) from the membrane (particulate GC) preferentially regulates targets localised in the plasma membrane, such as ion channels, probably due to a PKG-dependent localised action (Rho et al., 2002; Zhang et al., 2005). Furthermore, in vascular smooth muscle cells, Piggott et al. (2006) showed that ANP, but not the nitric oxide donors, induces activation of cyclic nucleotide-gated channels, suggest- ing the existence of localised cGMP signals in these cells. We showed previously that testosterone induces vasorelaxation mediated by European Journal of Pharmacology 640 (2010) 94–101 ⁎ Corresponding author. Tel.: + 351 275 329049; fax: + 351 275 329099. E-mail address: iverde@fcsaude.ubi.pt (I. Verde). 0014-2999/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ejphar.2010.04.025 Contents lists available at ScienceDirect European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar