• YAKHAK HOEJI
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• v.34 no.3
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• pp.180-191
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• 1990

A comparison was made of the effects of selective ${\alpha_1}-adrenoceptor$ agonist phenylephrine and selective ${\alpha_2}-adrenoceptor$ agonist clonidine on endothelium-containing and endothelium-denuded rings of the rat aorta. In the case of phenylephrine, removal of endothelium increased sensitivity 2.5 fold at $EC_{50}$ level and maximum contractive response 1.4 fold. In the case of clonidine, which gave only 15% of maximum contractive response given to phenylephrine on endothelium-containing rings, removal of the endothelium increased sensitivity 5.6 fold at $EC_{50}$ level and maximum contractive response 5 fold, which was about 55% of that given by phenylephrine. In endothelium-denuded ring, phenylephrine-induced contraction tended to be more increased in tonic contraction than in phasic contraction as compared to that in endothelium-containing ring, while clonidine-induced contraction was monophasic and was increased only in tonic contraction. In the calcium-free solution or in the presence, of verapamil, contraction stimulated by clonidine was almost abolished while that stimulated by phenylephrine produced only phasic contraction. The depression of sensitivity to these agonists in rings with endothelium appeared to be due to the vasodepressor action of endothelium derived relaxing factor (EDRF), because hemoglobin, a specific blocking agent of EDRF, abolished this depression. It is unlikely that the endothelium-dependent relaxation was due to stimulation of release of EDRF, because clonidine did not produce endothelium-dependent relaxation in 5-hydroxytryptamine-precontracted ring even when its contractile action was blocked by the ${\alpha_1}-adrenoceptor$ antagonist, prazosin. When the efficacy of phenylephrine was reduced to about the initial efficacy of clonidine by pretreatment with dibenamine, the contraction-response curves for phenylephrine became very similar to the corresponding curves obtained for clonidine before receptor inactivation. In the dibenamine-treated rings, contraction of phenylephrine was abolished in calcium-free solution or in the presence of verapamil like that obtained for clonidine before receptor inactivation. These results suggest that EDRF spontaneously released from endothelium depress contraction more profoundly in a case of an agonist with low efficacy and the phenylephrine-induced contraction was totally dependent on extracellular calcium as was that obtained for clonidine when the efficacy of phenylephrine was reduced to that of clonidine by irreversible inactivation of ${\alpha_1}-adrenoceptor$ with dibenamine.

• The Korean Journal of Physiology and Pharmacology
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• v.18 no.6
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• pp.489-495
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• 2014

Protease-activated receptor (PAR)-2 is expressed in endothelial cells and vascular smooth muscle cells. It plays a crucial role in regulating blood pressure via the modulation of peripheral vascular tone. Although some reports have suggested involvement of a neurogenic mechanism in PAR-2-induced hypotension, the accurate mechanism remains to be elucidated. To examine this possibility, we investigated the effect of PAR-2 activation on smooth muscle contraction evoked by electrical field stimulation (EFS) in the superior mesenteric artery. In the present study, PAR-2 agonists suppressed neurogenic contractions evoked by EFS in endothelium-denuded superior mesenteric arterial strips but did not affect contraction elicited by the external application of noradrenaline (NA). However, thrombin, a potent PAR-1 agonist, had no effect on EFS-evoked contraction. Additionally, ${\omega}$-conotoxin GVIA (CgTx), a selective N-type $Ca^{2+}$ channel ($I_{Ca-N}$) blocker, significantly inhibited EFS-evoked contraction, and this blockade almost completely occluded the suppression of EFS-evoked contraction by PAR-2 agonists. Finally, PAR-2 agonists suppressed the EFS-evoked overflow of NA in endothelium-denuded rat superior mesenteric arterial strips and this suppression was nearly completely occluded by ${\omega}$-CgTx. These results suggest that activation of PAR-2 may suppress peripheral sympathetic outflow by modulating activity of $I_{Ca-N}$ which are located in peripheral sympathetic nerve terminals, which results in PAR-2-induced hypotension.

• The Korean Journal of Physiology
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• v.21 no.1
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• pp.35-46
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• 1987

It has been well known that estrogens stimulate the uterine contractility and progestins inhibit it. Then, one may expect that the uterine contractility and sensitivities to oxytocin (OT) and prostaglandin $F_{2{\alpha}}\;(PGF_{2{\alpha}})$ would be different among the estrus cycle. These hypotheses were tested using the mature female rat. Spontaneous isometric contractions of isolated uterine strips $(1{\times}0.3\;cm)$ from cyclic rats in various stages of the estrus cycle, bilateral ovarectomized rats and hypophysectomized rats were recorded in absence or presence with $estradiol-17{\beta}\;(E_2)$, progesterone $(P_4)$, OT and $PGF_{2{\alpha}}$. The results were summarized as follows: 1) The spontaneous uterine contractile force was the highest in the estrus rat and the lowest in the ovarectomized or the hypophysectomized rat. In the proestrus rat, the contractile frequency was the lowest (2.7 beats/10 min) and the contractile duration was the longest (70 sec). In the other groups, there were no any differencies in frequency (9 beats/10 min) and in duration (30 sec). 2) OT and $PGF_{2{\alpha}}$ stimulated the uterine contractility in all groups tested except in the hypophysectomized rat in which OT failed to stimulate the uterine contraction. $PGF_{2{\alpha}}$ was more effective in stimulating the uterine contraction than OT in all groups tested except in the estrus rat. OT-induced contraction was the highest in the estrus rat and $PGF_{2{\alpha}}-induced$ contraction was the lowest in the hypophysectomized rat. 3) Uterine contractilities were not changed by the in vitro treatments of $E_2$ or $P_4$ under the influence of endogenous steroids, however, $E_2$ and $P_4$ stimulated the uterine contraction in the ovarectomized rat in which endogenous steroids were almost abolished. 4) Increased uterine contraction by the treatment of OT was suppressed by in vitro $E_2$ or $P_4$ in the estrus rat, while it was potentiated by the $P_4$ in the proestrus rat. In other groups, exogenous $E_2$ or $P_4$ did not affect the OT-induced uterine contraction. 5) $PGF_{2{\alpha}}-induced$ uterine contraction was suppressed in the ovarectomized rat by $E_2$ and $P_4$, in the diestrus and proestrus rats by $P_4$ and in the hypophysectomized rat by $E_2$. In other groups, exogenous $E_2$ or $P_4$ was ineffective in altering the $PGF_{2{\alpha}}-induced$ uterine contraction. According to the above results, it may conclude that the mechanisms of the different uterine contractility and the different uterine sensitivity to OT or $PGF_{2{\alpha}}$ according to the estrus cycle are not explicable with only the serum concentrations of steroids, OT and $PGF_{2{\alpha}}$ but also other unknown factors.

• The Korean Journal of Physiology and Pharmacology
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• v.13 no.6
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• pp.503-510
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• 2009

To elucidate the mechanism of cyclic nucleotides, such as adenosine 3',5'-cyclic monophosphate (cAMP) and guanosine 3',5'-cyclic monophosphate (cGMP), in the regulation of human gastric motility, we examined the effects of forskolin (FSK), isoproterenol (ISO) and sodium nitroprusside (SNP) on the spontaneous, high $K^+$ and acetylcholine (ACh)-induced contractions of corporal circular smooth muscle in human stomach. Gastric circular smooth muscle showed regular spontaneous contraction, and FSK, ISO and SNP inhibited its phasic contraction and basal tone in a concentration-dependent manner. High $K^+$ (50 mM) produced sustained tonic contraction, and ACh $(10\;{\mu}M)$ produced initial transient contraction followed by later sustained tonic contraction with superimposed phasic contractions. FSK, ISO and SNP inhibited high $K^+$-induced tonic contraction and also ACh-induced phasic and tonic contraction in a reversible manner. Nifedipine $(1\;{\mu}M)$, inhibitor of voltage-dependent L-type calcium current $(VDCC_L)$, almost abolished ACh-induced phasic contractions. These findings suggest that FSK, ISO and SNP, which are known cyclic nucleotide stimulators, inhibit smooth muscle contraction in human stomach partly via inhibition of $VDCC_L$.

• Korean Journal of Veterinary Research
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• v.43 no.3
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• pp.405-414
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• 2003

The purpose of this study was to assess the role of tachykinins (TK) in mediating nonadrenergic noncholinergic (NANC) contractions produced by electrical field stimulation (EFS) in the longitudinal muscle of the rat ileum. In the presence of atropine ($1{\mu}M$), guanethidine ($5{\mu}M$), and L-nitroarginine (L-NNA, $200{\mu}M$), EFS (0.5ms pulse duration, 120 V, 1-20 Hz for 2 min) produced a frequency-dependent slowly-developing tonic contraction with superimposed phasic contractions ('on'-contraction) followed by off slowly-decreasing tonic and superimposed phasic contractions ('off'-contraction) of mucosa-free longitudinal oriented muscle strip. These EFS induced responses were blocked by tetrotoxin. $NK_1$ receptor selective antagonist L-732,138 strongly inhibited the EFS-induced excitatory responses. However $NK_2$ receptor selective antagonist, GR 159897 and $NK_3$ receptor selective antagonist SB 222200 did not significantly inhibited the responses. $NK_1$ receptor selective agonist [$Sar^9$,$Met(O_2)^{11}$] Substance P and $NK_2$ receptor selective agonist [${\beta}-Ala^8$]-neurokinin A (4-10) induced tonic contraction with superimposed phasic contractions of longitudinal oriented muscle strip and almost blocked by selective antagonist L-732,138 and GR 159897, respectively. But $NK_3$ receptor selective agonist senktide did not showed any effect. Nifedipine ($1{\mu}M$) abolished the contraction produced either by EFS or by the TK receptor agonists [$Sar^9$,$Met(O_2)^{11}$] Substance P or [${\beta}-Ala^8$]-neurokinin A (4-10). It is concluded that, in the longitudinal muscle of rat ileum, both $NK_1$ and $NK_2$ receptors modulated the responses to exogenous tachykinins, whereas $NK_1$ is mainly involved in NANC neuromuscular contraction.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.3 s.246
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• pp.255-261
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• 2006

Flow characteristics of DI water in a microchannel with a stenosis were investigated using .a micro PIV system with varying flow rate. The width and depth of the PDMS micro-channel were $100{\mu}m\;and\;50{\mu}m$, respectively. To Investigate flow characteristics in the micro-stenosis, the same experiment was carried out in a straight microchannel under the same flow rate. The measured mean velocity fields were almost symmetric with respect to the channel centerline. The experimental results are well agreed with the theoretical Hagen-Poiseuille profile. In the contraction part of the micro-stenosis, the oncoming flow is accelerated rapidly and the maximum velocity occurs at the throat, almost 4.99 time faster than that without the stenosis.

• Journal of the Korean Mathematical Society
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• v.46 no.5
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• pp.1071-1085
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• 2009

This paper considers the problem of existence and exponential stability of almost periodic solution for shunting inhibitory cellular neural networks with distributed delays and large impulses. Based on the contraction principle and Gronwall-Bellman's inequality, some sufficient conditions are obtained. The results of this paper are new and they complement previously known results.

• Korea-Australia Rheology Journal
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• v.16 no.4
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• pp.183-191
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• 2004

High Deborah or Weissenberg number problems in viscoelastic flow modeling have been known formidably difficult even in the inertialess limit. There exists almost no result that shows satisfactory accuracy and proper mesh convergence at the same time. However recently, quite a breakthrough seems to have been made in this field of computational rheology. So called matrix-logarithm (here we name it tensor-logarithm) formulation of the viscoelastic constitutive equations originally written in terms of the conformation tensor has been suggested by Fattal and Kupferman (2004) and its finite element implementation has been first presented by Hulsen (2004). Both the works have reported almost unbounded convergence limit in solving two benchmark problems. This new formulation incorporates proper polynomial interpolations of the log­arithm for the variables that exhibit steep exponential dependence near stagnation points, and it also strictly preserves the positive definiteness of the conformation tensor. In this study, we present an alternative pro­cedure for deriving the tensor-logarithmic representation of the differential constitutive equations and pro­vide a numerical example with the Leonov model in 4:1 planar contraction flows. Dramatic improvement of the computational algorithm with stable convergence has been demonstrated and it seems that there exists appropriate mesh convergence even though this conclusion requires further study. It is thought that this new formalism will work only for a few differential constitutive equations proven globally stable. Thus the math­ematical stability criteria perhaps play an important role on the choice and development of the suitable con­stitutive equations. In this respect, the Leonov viscoelastic model is quite feasible and becomes more essential since it has been proven globally stable and it offers the simplest form in the tensor-logarithmic formulation.

• Proceedings of the Korean Society of Applied Pharmacology
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• 1996.04a
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• pp.202-202
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• 1996

The antihistaminic action of eighteen herbal medicines was investigated by the radioligand binding and functional assays. The hexane fractions of Trichosanthis radix, Mori cortex radicis and Evodiae fructus dose-dependently inhibited [$^3$H]mepyramine binding to H$_1$ receptor and histamine-induced contraction in guinea-pig brain homogenates and isolated guinea-pig ilea, respectively. Antihistaminic action of the hexane and ethylacetate fractions of Mori cortex radicis and the hexane fraction of Evodiae fructus was more potent than their antimuscarinic action evaluated from the inhibition of [$^3$H]QNB binding and carbachol response. The ethylacetate and chloroform fractions and six known flavonoids from Scutellariae radix also inhibited histamine-induced contraction, but antihistaminic potencies of these fractions and compounds were almost identical with their antimuscarinic potencies. The hexane fractions of Mori cortex radicis and Evodiae fructus, as shown in ketotifen, inhibited selectively the increase of cutaneous vascular permeability induced by histamine. However, wogonin (SC-1) from Scutellariae radix was a nonselective inhibitor for the effect of histamine and serotonin on the vascular permeability. These results demonstrate that the hexane and ethylacetate fractions of Mori cortex radicis and the hexane fraction of Evodiae fructus have the selective histamine H$_1$ receptor blocking activities.

• Biomolecules & Therapeutics
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• v.4 no.1
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• pp.36-45
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• 1996

The antihistaminic action of eighteen herbal medicines was investigated by the radioligand binding and functional assays. The hexane fractions of Trichosanthis radix, Mori cortex radicis and Evodiae fructus dosedependently inhibited [$^3$H] mepyramine binding to H$_1$, receptor in guinea-pig brain homogenates and histamine-induced contraction of isolated guinea-pig ileum. Antihistaminic action of the hexane and ethyl acetate fractions of Mori cortex radicis and the hexane fraction of Evodiae fructus was more potent than their antimuscarinic action evaluated from the inhibition of [$^3$H]QNB binding and carbachol response. The ethyl acetate and chloroform fractions from Scutellariae radix also inhibited histamine-induced contraction, but antihistaminic potencies of these fractions were almost identical with their antimuscarinic potencies. The hexane fractions of Mori cortex radicis and Evodiae fructus inhibited selectively the increase of histamine-induced cutaneous vascular Permeability in the rat dorsal skins. However, the ethyl acetate fraction from Scutellariae radix inhibited eqipotently the effects of histamine and serotonin on the vascular permeability. These results demonstrate that the hexane and ethyl acetate fractions of Mori cortex radicis and the hexane fraction of Evodiae fructus have the selective histamine H$_1$receptor blocking activity.