HNS-32, a novel azulene-1-carboxamidine derivative, inhibits nifedipine-sensitive and -insensitive contraction of the isolated rabbit aorta

Abstract.

The vasorelaxant profile of a novel azulene-1-carboxamidine derivative, HNS-32 [N ¹,N ¹-dimethyl-N ²-(2-pyridylmethyl)-5-isopropyl-3,8-dimethyl-azulene-1-carboxamidine, CAS 186086-10-2], was investigated in the isolated rabbit aorta precontracted with high KCl, noradrenaline (NA) or phorbol 12, 13-dibutyrate (PDBu) and compared with those of nifedipine and nitroglycerin. In preparations without endothelium, HNS-32 elicited concentration-dependent, full inhibition of contractions elicited by high KCl (80 mM), NA (3×10^–6 M) or PDBu (10^–6 M). In contrast, nifedipine inhibited only the contraction elicited by membrane depolarization with high KCl. Nitroglycerin also attenuated high-KCl-, NA- and PDBu-elicited contractions effectively, although full suppression was obtained only for NA-elicited contraction. Whilst the relaxant effect of HNS-32 was not affected by the presence of endothelium, the relaxant response to acetylcholine was endothelium dependent. Addition of excess Ca²⁺ restored both the HNS-32-reduced tension in muscle precontracted with high KCl and the nifedipine-mediated tension decrease. Relaxation elicited by HNS-32 was not affected by the adenylate cyclase inhibitor, 9-(tetrahydro-2′-furyl)adenine (SQ 22,536, 10^–4 M), the soluble guanylate cyclase inhibitor, 1H-(1,2,4)-oxadiazolo-(4,3-a)-quinoxalin-1-one (ODQ, 10^–5 M) or a cocktail of K⁺ channel blockers (glybenclamide 10^–6 M, tetraethylammonium 2×10^–3 M, apamin 10^–7 M, 4-aminopyridine 10^–4 M and Ba²⁺ 10^–5 M). These findings indicate that HNS-32 inhibits both L-type Ca²⁺ channel-dependent and -independent vascular contraction. Blockade of Ca²⁺ entry through L-type Ca²⁺ channels may be involved in the inhibitory effect of HNS-32 on the contraction due to membrane depolarization with high KCl. On the other hand, HNS-32 seems to inhibit Ca²⁺ channel-independent contraction via mechanism(s) other than elevation of cyclic nucleotides (cAMP and cGMP) and opening of K⁺ channels.