Non-genomic estrogen receoptor (ER) beta signalling is still not characterized. It has been recently reported that a putatively selective ERbeta agonist DPN (diarylpropiolnitrile) and genistein can acutely relax precontracted isolated mesentericarteries from male rats, although with less relative potency than 17beta-estradiol or ERalpha agonists. A different pattern of response was found in aortic preparations, where DPN showed similar relative potency as 17beta-estradiol in precontracted isolated rat aortic rings from male rats, and more relative potency than ERalpha agonists in aortic rings from both, male and female rats. In contrast with ERalpha agonists, the vasorelaxant action of DPN was largely endothelium-independent.

Interest in ERbeta vasorelaxation was raised by the observation that ERbeta-deficient mice develop sustained hypertension as they age. Therefore we decided to investigate acute ERbeta-signalling mechanism in isolated aortic smooth muscle from male rats. DPN was therefore tested in this preparation, for its effects on cyclic AMP (cAMP) contents, membrane potential, calcium signal and vascular tension.

Vasorelaxant responses to DPN (50 mM) were investigated in aortic rings preincubated with different compounds (n= 6-12 per condition). The protein kinase A (PKA) inhibitors Rp-8-Br-cAMPS (8-bromoadenosine-3', 5'-cyclic monophosphorothioate, Rp-isomer) and H-89 (N-[2-bromocynnamyl(amino)ethyl]-5-isoquinoline sulfonamide HCl) reduced DPN-induced vasorelaxation by a similar extent (-73%). Conversely, the protein kinase G (PKG) inhibitor Rp-8-Br-cGMP was inactive in this test. Vasorelaxant responses to DPN were also largely reduced (-65.5%) by the adenylate cyclase inhibitor MDL12330A (cis-N-[2-phenylcyclopentyl]-azacyclotridec-1-en-2-amine]). The CFTR inhibitor DPC (diphenylamine-2-carboxylic acid) strongly antagonized DPN vasorelaxation (-76.4%). Finally, it is interesting to mention that the PKA inhibitor Rp-8-Br-cAMPS (100 mM) partially reversed (-61.3%, n=4) the antagonistic action of DPN on phenylephrine-induced calcium signal in isolated aortic smooth muscle cells.