Fumiko Yamaki

Relaxant Action of Azulene‐1‐carboxamidine Derivative N1, N1‐dimethyl‐N2‐(2‐pyridylmethyl)‐5‐isopropyl‐3,8‐dimethylazulene‐1‐carboxamidine (HNS‐32) in Pig Coronary Artery

HNS-32 (N1N1-dimethyl-N2-(2-pyridylmethyl)-5-isopropyl-3,8-dimethylazulene-1-carbox-amidine) (CAS 186086-10-2) is a newly synthesized compound with an azulene structure within the molecule. The coronary relaxant action of HNS-32 was investigated pharmaco-mechanically on isolated pig coronary artery. The effects of HNS-32 were compared with diltiazem, a Ca2+-channel blocker. HNS-32 inhibited sustained contractions evoked by high KCl, prostaglandin F2α, a thromboxane A2 mimetic (U46619) and endothelin-1 in a concentration-dependent manner. The potency of HNS-32 to inhibit these contractions was 5- to 40-times lower than diltiazem. HNS-32 also diminished phasic contractions induced by acetylcholine, histamine and 5-hydroxytryptamine. Addition of excess Ca2+ counteracted HNS-32-induced inhibition of high KCl-induced contraction only by approximately 10% whereas it restored diltiazem-induced inhibition by about 50%. Suppression of the contractile response to a phorbol ester (phorbol 12,13-dibutyrate) by HNS-32 was approximately 40%. HNS-32 prevents coronary contractions produced by a wide variety of spasmogens. Although inhibitions of L-type Ca2+ channels and protein kinase C may be partly responsible for HNS-32 action, some direct action on the contractile systems seems to be involved in the coronary relaxation by HNS-32.

NO-mediated MaxiKCa channel activation produces relaxation of guinea pig aorta independently of voltage-dependent L-type Ca2+ channels

(1) The role of L-type Ca2+ channels in the relaxation to nitric oxide (NO)-mediated MaxiKCa channel activation was examined in guinea pig aorta. (2) Acetylcholine (ACh) produced an endothelium-dependent relaxation of guinea pig aorta precontracted with noradrenaline (NA), which was abolished by an NO synthase inhibitor, NG-nitro-l-arginine (l-NNA). (3) Both endothelium-dependent relaxation by ACh and endothelium-independent relaxation by an NO donor, (±)-(E)-ethyl-2-[(E)-hydroxyimino]-5-nitro-3-hexeneamide (NOR3), were strongly suppressed by a soluble guanylate cyclase (sGC) inhibitor, 1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one (ODQ), suggesting that increased intracellular cGMP plays the key role in both responses. (4) ACh- and NOR3-induced relaxations were significantly suppressed by iberiotoxin (IbTX), a selective blocker of MaxiKCa channels. (5) ACh- and NOR3-induced relaxations were greatly attenuated when arteries were precontracted with high KCl instead of NA, supporting the idea that K+ channel activation mediates the relaxant responses. (6) NOR3-induced relaxations were not affected by a L-type Ca2+ channel blocker, diltiazem. Furthermore, endothelium-independent relaxation by a KATP channel opener, (+)-7,8-dihydro-6,6-dimethyl-7-hyroxy-8-(2-oxo-1-piperidinyl)-6H-pyrano[2,3-f]benz-2,1,3-oxadiazole (NIP-121) was not affected by diltiazem and nicardipine. (7) These findings suggest that blockade of L-type Ca2+ channels is not a major mechanism responsible for the vascular relaxation due to NO-mediated MaxiKCa channel activation in guinea pig aorta.

Endothelium is involved in the vasorelaxation by an ATP-sensitive K+ channel opener, NIP-121.

Possible involvement of endothelium was examined in the vasorelaxation of rat aorta in response to NIP-121 ((+)-7,8-dihydro-6,6-dimethyl-7-hyroxy-8-(2-oxo-1-piperidinyl)-6H- pyrano[2,3-f]benz-2,1,3-oxadiazole), an ATP-sensitive K+ (K(ATP)) channel opener. The NIP-121-induced vasorelaxation was greater in endothelium-intact preparations than in endothelium-denuded ones. In the presence of glibenclamide, which inhibits K(ATP) channels, NIP-121-induced vasorelaxations were of a similar extent in both endothelium-intact and -denuded preparations. These findings suggest that the presence of endothelium plays a role in the vasorelaxation in response to K(ATP) channel openers.

Nitric Oxide Accounts for Endothelium‐dependent Relaxation of Pig Coronary Artery in Response to Noradrenaline

Vasorelaxant substances responsible for endothelium-dependent relaxation of pig coronary artery in response to noradrenaline have been investigated pharmacologically. Noradrenaline relaxed pig coronary artery in an endothelium- and concentration-dependent way in the presence of prazosin (10−6 M) and propranolol (3 times 10−6 M), to block α1- and β-adrenoceptors in smooth muscle cells. Prazosin- and propranolol-resistant endothelium-dependent relaxation of the coronary artery to noradrenaline was greatly attenuated by the NO synthase inhibitor, NG-nitro-L-arginine methyl ester (L-NAME) (10−4 M) and the soluble guanylate cyclase inhibitor (1H-[1,2,4]-oxadiazolo-[4,3-a]-quinoxalin-1-one, ODQ; 10−5 M). Noradrenaline-induced endothelium-dependent coronary relaxation in the presence of prazosin and propranolol was almost abolished by rauwolscine (3 times 10−6 M), a selective α2-adrenoceptor antagonist. These findings suggest that noradrenaline-induced endothelium-dependent relaxation of pig coronary artery is largely mediated by release of endothelium-derived NO as a consequence of the stimulation of endothelial α2-adrenoceptors.

β-Adrenoceptor subtypes and cAMP role in adrenaline- and noradrenaline-induced relaxation in the rat thoracic aorta

Object We identified the β-adrenoceptor (β-AR) subtypes responsible for the relaxant responses to adrenaline (AD) and noradrenaline (NA) in the rat thoracic aorta and examined the role of cAMP which is involved in these relaxant responses. Methods The effects of β-AR antagonists or the adenylyl cyclase inhibitor SQ 22,536 on AD- and NA-induced relaxant responses in phenylephrine-induced contraction and increases in cAMP levels were examined in isolated, endothelium-denuded rat thoracic aorta segments. Results AD-induced relaxation was completely suppressed by propranolol (10−7 M) or by ICI-118,551 (10−8 M) plus atenolol (10−6 M), and was also very strongly inhibited by ICI-118,551 (10−8 M) alone. AD (10−5 M) increased tissue cAMP levels by approximately 1.9-fold compared with that in non-stimulated aortic tissue, but did not significantly increase cAMP levels in the presence of ICI-118,551 (10−8 M) or SQ 22,536 (10−4 M). AD-induced relaxation was strongly suppressed by SQ 22,536 (10−4 M). NA-induced relaxation was almost completely suppressed by atenolol (10−6 M) plus ICI-118,551 (10−8 M) although it was hardly affected by ICI-118,551 (10−8 M) alone. NA (10−5 M) increased tissue cAMP levels by approximately 2.2-fold compared with that in non-stimulated aortic tissue, but did not significantly increase cAMP levels in the presence of atenolol (10−6 M) or SQ 22,536 (10−4 M). NA-induced relaxation was strongly suppressed by SQ 22,536 (10−4 M). Conclusion In rat thoracic aorta, AD- and NA-induced relaxations, which are both strongly dependent on increased tissue cAMP levels, are mainly mediated through β2- and β1-adrenoceptors respectively.

Pharmacological identification of β-adrenoceptor subtypes mediating isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle

Object We aimed to identify the β-adrenoceptor (β-AR) subtypes involved in isoprenaline-induced relaxation of guinea pig colonic longitudinal smooth muscle using pharmacological and biochemical approaches. Methods Longitudinal smooth muscle was prepared from the male guinea pig ascending colon and contracted with histamine prior to comparing the relaxant responses to three catecholamines (isoprenaline, adrenaline, and noradrenaline). The inhibitory effects of subtype-selective β-AR antagonists on isoprenaline-induced relaxation were then investigated. Results The relaxant potencies of the catecholamines were ranked as: isoprenaline > noradrenaline ≈ adrenaline, whereas the rank order was isoprenaline > noradrenaline > adrenaline in the presence of propranolol (a non-selective β-AR antagonist; 3 × 10−7 M). Atenolol (a selective β1-AR antagonist; 3 × 10−7–10−6 M) acted as a competitive antagonist of isoprenaline-induced relaxation, and the pA2 value was calculated to be 6.49 (95% confidence interval: 6.34–6.83). The relaxation to isoprenaline was not affected by ICI-118,551 (a selective β2-AR antagonist) at 10−9–10−8 M, but was competitively antagonized by 10−7–3 × 10−7 M, with a pA2 value of 7.41 (95% confidence interval: 7.18–8.02). In the presence of propranolol (3 × 10−7 M), the relaxant effect of isoprenaline was competitively antagonized by bupranolol (a non-selective β-AR antagonist), with a pA2 value of 5.90 (95% confidence interval: 5.73–6.35). Conclusion These findings indicated that the β-AR subtypes involved in isoprenaline-induced relaxation of colonic longitudinal guinea pig muscles are β1-AR and β3-AR.