• YAKHAK HOEJI
• /
• v.35 no.5
• /
• pp.416-426
• /
• 1991

The effects of an irreversible or a reversible $\alpha_1$-adrenoceptor antagonist (dibenamine or prazosin) on $\alpha_1$-adrenoceptor-mediated vasoconstrictions were studied in the endothelium-denuded rat aorta. In these experiments, the mobilization of intracelluier calcium and translocation of extracellular calcium were also studied. To exclude the modulation of endothelium releasing EDRF and EDCF, the endothelium was removed in all rat aortas. Contraction induced by phenylephrine (a full $\alpha_1$-adrenoceptor agonist) was separated into a fast phasic component of the response due to the release of intracellular calcium and a slow tonic one due to the influx of extracellular calcium. Pretreatments with increasing doses of reversible $\alpha_1$-adrenoceptor antagonist prazosin, as well as irreversible $\alpha_1$-adrenoceptor antagonist dibenamine, inhibited the phasic component of phenylephrine-induced contraction more effectively than the tonic one. Pretreatment of dibenamine (0.2 $\mu{M}$) or prazosin (10 nM) to the rat aorta abolished phasic response but remained tonic one about 41% and 51%, respectively. These results suggest that as the efficiency of phenylephrine was progressively reduced by pretreatments with increasing doses of an irreversible or a reversible $\alpha_1$-adrenoceptor antagonist (dibenamine or prazosin), the contraction induced by phenylephrine became progressively more dependent on the influx of extracellular calcium.

• Korean Journal of Veterinary Service
• /
• v.17 no.3
• /
• pp.255-263
• /
• 1994

To elucidate the action of the adrenergic nerve on the isolated uterine smooth muscle of the pig, effects of electrical transmural nerve stimulation and norepinephrine were investigated on the pretreatment of phentolamine ； non-selective ${\alpha}$-adrenoceptor blocker, propranolol ; ${\beta}$-adrenoceptor blocker and the yohimbine；${\alpha}_2$-selective adrenoceptor blocker from physiograph. 1. The relaxation response induced by norepinephrine was the concentration of $10^{-6}$ M at first and maximum response was concentration of $10^{-4}$M. 2. The relaxation response induced by norepinephrine was not effected by the pretreatment with non-selective $\alpha$-adrenoceptor blocker, phentolanune ($10^{-6}$ M) but was completely blocked by the pretreatment with ${\beta}$-adrenoceptor blocker, propranolol($10^{-6}$ M). 3. The contractile response induced by electrical transmural nerve stimulation(20V, 10Hz, 0.5msec, 20sec ) was inhibited by the pretreatment with non-selective ${\alpha}$-adrenoceptor blocker, phentolamine($10^{-6}$ M) but was not inhibited and rather increased by the pretreatment ${\beta}$-adrenoceptor blocker, propranolol($10^{-6}$ M), and was not approximately effected by the pretreatment with ${\alpha}_2$-adrenoceptor blocker, yohimbine($10^{-6}$ M). These finding suggest that it was excitatory action by ${\alpha}_1$-adrenergic nerve and inhibitory action by ${\alpha}_2$-adrenergic, ${\beta}$-adrenergic nerve on uterine smooth muscle of the pig.

• Korean Journal of Clinical Pharmacy
• /
• v.33 no.2
• /
• pp.86-96
• /
• 2023

Background: Using KIDS-KAERS database (KIDS-KD) from 2016 to 2020, the aim is to investigate signals of adverse events of alpha-adrenoceptor antagonists and to present adverse events that are not included in the precautions for use when marketing approval. Methods: This study was conducted by disproportionality analysis. Data mining analysis was performed to detect signals of alpha-adrenoceptor antagonists, such as terazosin, doxazosin, alfuzosin, silodosin, and tamsulosin. The signal was defined by three criteria as proportional reporting ratio (PRR), reporting odds ratio (ROR), and information component (IC). Detected signals were compared with product labeling and the European Medicines Agency-Important Medical Events list. Results: Out of the total number of 408,077 reports for adverse events, 6,750 cases were reported as adverse events of alpha-adrenoceptor antagonists. Dizziness, mouth dryness, hypotension postural, and oedema peripheral are identified as common adverse events of five alpha-adrenoceptor antagonists and are typically listed on drug labels. However, new signals were detected for pneumonia, chronic obstructive airway disease, eye diseases such as glaucoma and cataracts, fracture, and ileus of tamsulosin that were not previously listed on the drug labels in Korea. Conclusions: This study identified signals related to adverse drug reactions of alpha-adrenoceptor antagonists and presented serious adverse events, suggesting new adverse reactions to be aware of when using alpha-adrenoceptor antagonists.

• The Korean Journal of Physiology
• /
• v.27 no.1
• /
• pp.27-35
• /
• 1993

Effects of the endothelium on the contractile responses to norepinephrine (NE) were investigated in isolated helical strips of the proximal and distal coronaries artery of pigs. The helical strips were immersed in Tris-buffered Tyrode's solution equilibrated with 100% $O_2$ at $35^{\circ}C$ and its isometric tension was measured. NE relaxed the strips precontracted with acetylcholine from both the proximal and distal coronary artery. NE-induced relaxation, which might be induced mainly by $\beta$-adrenoceptor function was dominant in the distal coronary arteries. NE-induced relaxation was converted to a contraction after $\beta$-adrenoceptor blockade with propranolol $(3{\times}10^{-6}M)$. ${\alpha}$-adrenoceptor-mediated contraction by NE was greater in the proximal coronary artery than the distal coronary artery. Quantitatively, ${\alpha}_1$-adrenoceptor mediated contraction by NE was greater than ${\alpha}_2$-adrenoceptor mediated contraction by NE in both arteries. NE-induced relaxation was decreased by rubbing of endothelium in both arteries. ${\alpha}_1-and\;{\alpha}_2$-adrenoceptor mediated contraction by NE were potentiated by rubbing of endothelium in both arteries. Pretreatment with methylene blue, an inhibitor of soluble guanylate cyclase, increased ${\alpha}_1-\;and\;{\alpha}_2$-adrenoceptor mediated contraction by NE in both arteries with endothelium. From the above results, we suggest that the effect of activation of $\alpha$-adrenoceptors by NE may be modulated by endothelium in the proximal and distal coronary arteries of pigs. This effect may be mediated via endothelium derived relaxing factor.

• The Korean Journal of Pharmacology
• /
• v.22 no.1 s.38
• /
• pp.45-50
• /
• 1986

The involvement of central $_{{\alpha}2}$-adrenoceptors in the development of muricide (mouse-killing behavior) in the olfactoly bulbectomized (OB) rats was strudied. The fractional turnover rate of noradrenaline (NA) in forebrain from OB muricidal rats was significantly lowered than that from sham rats. However, after yohimbine or idazoxan treatment, NA turnover was significantly increased in concert with inhibition of the development of muricide in OB rats. By radioligand binding studies with $[^3H]$ yohimbine, the maximum binding $(B_{max})$ of $[^3H]$ yohimbine to cerebral cortical membrane from OB rats was significantly higher than that from sham rats without change of affinity for agonists and antagonists$(K_i)$. With these results it was suggested that muricidal behavior of OB rats has a close relevance to the hyperactivity of central $_{{\alpha}2}$-adrenoceptor system.

• The Korean Journal of Pharmacology
• /
• v.31 no.1 s.57
• /
• pp.39-51
• /
• 1995

The roles of ${\beta}-adrenoceptor$ were well known in hyperthyroidal heart, but not with ${\alpha}-adrenoceptor$. So we studied the effects of phenylephrine on membrane potential, intracellular sodium activity ($a^{i}_{Na}$), twitch force, and intracellular pH ($pH_i$) by continuous intracellular recordings with ion-selective and conventional microelectrodes in the papillary muscles of hyperthyroid guinea pig heart. ${\alpha}_1-adrenoceptor$ stimulation by phenylephrine (10^{-5}\;or\;3{\times}10^{-5}M$) produced the following changes: variable changes in action potential duration, a hyperpolarization ($1.5{\pm}0.1mM$) of the diastolic membrane potential, an increase in $a^{i}_{Na}\;(0.4{\pm}0.15mM)$, a stronger positive inotropic effect ($220{\pm}15%$), an increase in $pH_i\;(0.06{\pm}0.002\;unit)$. These changes were flocked by prazosin and atenolol. This indicated that the changes in membrane potential, $a^{i}_{Na}$ twitch force, and $pH_i$ are mediated by a stimulation of the ${\alpha}_1-adrenoceptor$. Ethylisopropylamiloride ($10^{-5}$) also blocked the increase in $a^{i}_{Na}$ and twitch force. On the other hand, strophanthidin, tetrodotoxin, $Cs^+$ or verapamil did not block the increase in $a^{i}_{Na}$ and twitch force. Thus, it was suggested that ${\alpha}_1-adrenoceptor$ stimulation increased $a^{i}_{Na}\;and\;pH_i$ by stimulation of $Na^{+}-H^{+}$ exchange, thereby allowing intracellular alkalinization and $a^{i}_{Na}$ increase. These results were very different from euthyroidal heart which showed ${\alpha}_1-adrenoceptor$-induced decrease in $a^{i}_{Na}$ and initial negative inotropic effect. From the above results, it was concluded that ${\alpha}_1-adrenoceptor$ had a important role in hyperthy-roidal heart.

• Korean Journal of Veterinary Research
• /
• v.36 no.2
• /
• pp.327-335
• /
• 1996

Recently in spite of the interest on the regulation of intracellular $Mg^{2+}$ by neurotransmitters or drugs, the magnesium ion($Mg^{2+}$) regulation by ${\alpha}_1$-adrenoceptor stimulation has not been studied in the heart yet. To elucidate the regulation of ${\alpha}_1$-adrenoceptor stimulation-induced $Mg^{2+}$ release and the effects of ${\alpha}_1$-adrenoceptor stimulation on pathophysiological conditions, in this study we have evaluated the effects of phenylephrine, PMA, $H_7$. staurosporine, verapamil and lidocaine on $Mg^{2+}$ release in perfused guinea pig heart. During preperfusion exogenous $Mg^{2+}$ was added to the medium to give 1.2mM 15min before starting to addition of drugs, and then the infusion of exogenous $Mg^{2+}$ was stopped. $Mg^{2+}$ in the perfusate leaving the heart was measured by atomic absorption spectrophotometry. $Mg^{2+}$ free solution produced an increase in heart rate and phenylephrine elicited $Mg^{2+}$ release from the heart. $Mg^{2+}$ release by phenylephrine was abolished by combined treatment with prazosin. By contrast, cardiac $Mg^{2+}$ uptake induced by a protein kinase C(PKC) activator, PMA was abolished by a selective PKC inhibitor, staurosporine. And the phenylephrine-induced $Mg^{2+}$ release was not affected by the PKC inhibitor, $H_7$. When verapamil or lidocaine was added to perfusing solution, $Mg^{2+}$ release was potentiated by phenylephrine from perfused guinea pig heart. These results suggest that ${\alpha}_1$-adrenoceptor stimulation caused $Mg^{2+}$ release and that PKC is not involved in ${\alpha}_1$-adrenoceptor mediated $Mg^{2+}$ release from perfused guinea pig heart. Under pathophysiological conditions, the $Mg^{2+}$ alteration by ${\alpha}_1$-adrenoceptor stimulation is considerable.

• YAKHAK HOEJI
• /
• v.30 no.3
• /
• pp.157-162
• /
• 1986

$\alpha$-Adrenoceptor subtypes in the isolated rat aortic strips were examined by using agonists and antagonists which have varying selectivity for $\alpha_1$- and $\alpha_2$- adrenoceptors. Norepinephrine and phenylephrine produced a similar magnitude of maximum contractions. $pA_2$ values for prazosin and yohimbine were not significantly different using norepinephrine or phenylephrine as the agonist, suggesting a single population of alpha-adrenoceptor. Contractile responses produced by alpha-agonists were antagonized more effectively by prazosin (approximately 1000 fold) than by yohimbine.

• The Korean Journal of Pharmacology
• /
• v.22 no.1 s.38
• /
• pp.24-33
• /
• 1986

To ascertain the existence of various adrenoceptors involved in active transport of sodium in the frog skin and to delineate their physiological roles, the influence of various adrenergic agonists and antagonists on the potential difference (PD), short-circuit current (SCC) and total skin conductance (TSC) of the isolated frog skin of Rana nigromaculata were investigated. PD and SCC were determined with Ussing's technique. Drugs were administered to the serosal side of the skin. Experimental results were summarized as follows: 1. The responses to norepinephrine (NE, $6{\times}10^{-8}-6{\times}10^{-5})M$), phenylephrine (PE, $5{\times}10^{-6}-5{\times}10^{-4}M$) and epinephrine (Epi, $5.5{\times}10^{-7}-5.5{\times}10^{-5}M$) were characterized by marked elevation of PD & SCC in dose-related fashion, but the maximal effect attained by Epi was less than those of NE and PE. 2. These increments of PD & SCC were significantly inhibited by prazosin $(2{\times}10^{-6}M)$, a speciflc ${\alpha}_1$-adrenoceptor blocker. The stimulatory effect on PD & SCC were completely abolished by phenoxybenzamine (PBZ, $3.3{\times}10^{-5}M$), an irreversible ${\alpha}$-adrenoceptor blocking agent. Furthermore, with a larger doses of Epi produced marked decline of PD & SCC after the PBZ pretreatment. 3. Isoproterenol (ISP), a ${\beta}$-adrenoceptor agonist, in concentrations ranging from $5{\times}10^{-7}$ to $5{\times}10^{-6}M$ produced dose-related decrease in PD & SCC, which could be abolished by pretreatment with propranolol $(4{\times}10^{-6}M)$, a specific ${\beta}$-adrenoceptor blocker. It was further noted that the effects of Epi on PD & SCC were markedly potentiated by Propranolol pretreatment. 4. Clonidine as well as guanabenz produced increases in PD & SCC and these effects were inhibited more specifically by prazosin pretreatment than by yohimbine. These results indicated that there exist in the frog skin two distinctive types of adrenoceptors, ${\alpha}$ and ${\beta}$, which roughly corresponds to those in mammals, and that the ${\alpha}$ type of adrenoceptors mediate the stimulation of PD & SCC, whereas ${\beta}$-adrenoceptors mediate the inhibition. However, based on evidence at hand, no conclusion could be drawn on the subtype of ${\alpha}$-adrenoceptors which is involved in the stimulation of sodium transport in the frog skin.

• The Korean Journal of Pharmacology
• /
• v.21 no.2
• /
• pp.90-98
• /
• 1985

1) In the study of the forced-swimming test in mice (FSM), the duration of immobility posture was dose-dependently shortened by ${\alpha}_2$-agonists, clonidine and guanabenz. BH-T 933 and oxymetazoline also decreased it . Xylazine rather increased the immobility duration at low dose. 2) ${\alpha}_1$-Agonists, cirazoline, amidephrine and methoxamine, however, showed inconsistent effect on the immobility duration (ID). 3) The decrease in ID by clonidine and guanabenz was antagonized by pretreatment with yohimbine, idazoxan and phentolamine (${\alpha}_2$antagonist), but not by prazosin and corynanthine (${\alpha}_1$-antagonist) .4) The ID in the FSM was shortened dose-dependently by d-amphetamine, and it was also antagonized by yohimbine, but not by prazosin. 5) In the mice pretreated with either ${\alpha}$-methyl-p-tyrosine or reserpine, or with combination of both, the decrease in ID was still evoked by clonidine. 6) When the mice were chronically treated with antidepressants (desipramine and imipramine), or with electroconvulsive shock, clonidine still decreased the ID as it did in the control. 7) These results provided the evidences to hypothesize that the change of the ID in the FSM is closely related with the postsynaptie ${\alpha}_2$-adrenoceptor located on the central noradrenergic neuron body. Furthermore, it is assumed that this escape-directed behavior enhanced by ${\alpha}_2$-adrenoceptor agonist may be the result in some analogy with the incentive of drives which are directed toward the self-preservation.