Perfused Rat Adrenal Medulla Research Articles

GINSENOSIDE-RG3 ENHANCES SOME ANTIHYPERTENSIVE AGENTS-INDUCED INHIBITION OF ADRENAL CATECHOLAMINE SECRETION

Objective: The present study was designed to examine the influence of ginsenoside-Rg3 (Rg3), one of panaxadiol-type saponins, which is isolated from Korean Panax ginseng, in some antihypertensive agents-induced inhibition on the secretion of catecholamines (CA) from the perfused rat adrenal medullae. Design and method: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: Ginsenoside-Rg3 (3∼30 μM) during perfusion into an adrenal vein for 90 min significantly inhibited the CA secretion evoked by acetylcholine (ACh). Also, olmesartan (AT1 receptor blocker, 15 μM), simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, 60 μM), enalapril (an inhibitor of angiotensin converting enzyme, 150 μM), and cilnidipine (a voltage-dependent L-type Ca2+ channel blocker, 3 μM) significantly reduced the CA secretion evoked by ACh and angiotensin II (Ang II), respectively. In the simultaneous presence of ginsenoside-Rg3 (10 μM) along with four antihypertensive agents (olmesartan, enalapril, simvastatin or cilnidipine), the CA secretion evoked by ACh and Ang II was more strongly inhibited compared with that of each antihypertensive agent-treatment alone. Conclusions: Collectively, these results demonstrate that ginsenoside-Rg3 as well as antihypertensive agents can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors from the perfused rat adrenal medulla. When this ginsenoside-Rg3 was used in combination with different antihypertensive agents, their effects of antihypertensive agents on reduction of adrenal CA secretion were significantly enhanced, which may also be clinically beneficial for the treatment of cardiovascular diseases.

PS-BPB04-3: ENHANCEMENT EFFECTS OF GINSENOSIDE-RG2 ON SOME ANTIHYPERTENSIVE AGENTS-INDUCED SUPPRESSION OF ADRENAL CATECHOLAMINE RELEASE

Objective: The present study was aimed to investigate the effects of ginsenoside-Rg2 (Rg2), one of panaxadiol-type saponins, which is isolated from Korean Red ginseng, in some antihypertensive agents-induced reduction on the release of catecholamines (CA) from the perfused model of the rat adrenal medullae. Design and Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. The CA amoiunt in the perfusate was measured directly by using the fluorospectrophotometer. Results: Ginsenoside-Rg2 (3∼30 μM) during perfusion into an adrenal vein for 90 min significantly inhibited the CA secretion evoked by acetylcholine (ACh) in a dose- and time-dependent fashion. Also, olmesartan (AT1 receptor blocker, 15 μM), simvastatin (an inhibitor of 3-hydroxy-3-methylglutaryl coenzyme A reductase, 60 μM), enalapril (an inhibitor of angiotensin converting enzyme, 150 μM), and cilnidipine (a voltage-dependent L-type Ca2+ channel blocker, 3 μM) significantly reduced the CA secretion evoked by ACh and angiotensin II (Ang II), respectively. In the simultaneous presence of ginsenoside-Rg2 (10 μM) along with four antihypertensive agents (olmesartan, enalapril, simvastatin or cilnidipine), the CA secretion evoked by ACh and Ang II was more strongly inhibited compared with that of each antihypertensive agent-treatment alone. Conclusion: Collectively, these results demonstrate that ginsenoside-Rg2 as well as antihypertensive agents can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors from the perfused rat adrenal medulla. When this ginsenoside-Rg2 was used in combination with different antihypertensive agents, their effects of antihypertensive agents on reduction of adrenal CA secretion were significantly enhanced, which may also be clinically beneficial for the treatment of cardiovascular diseases.

PS-B03-5: HIGH-DOSES OF LOSARTAN RATHER ENHANCE CATECHOLAMINE SECRETION FROM THE PERFUSED ADRENAL GLAND

Objective: Previously, we have found that Losartan (5∼50 μM), an AT1 receptor blocker, dose-dependently inhibits secretion of catecholamines (CA) evoked by cholinergic and angiotensin II (Ang II) receptor stimulation from the perfused rat adrenal medulla. The aim of the present study was to examine the characteristic effects of high-dose losartan on the CA secretion from the isolated perfused rat adrenal gland, and also to establish its mechanism of action. Design and Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: The perfusion of high-dose losartan (150 ∼ 600 μM) into an adrenal vein for 90 min resulted in great increases in CA secretions evoked by acetylcholine in a dose-dependent fashion. Also, losartan (300 μM) enhanced the CA release evoked by Ang II, high K+ and DMPP (a selective nicotinic receptor agonist), McN-A-343 (a selective muscarinic M1 receptor agonist). Also, in the presence of losartan (300 μM), the CA secretory responses to veratridine (a selective Na+ channel activator), Bay-K-8644 (a Ca2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor) were significantly potentiated, respectively. The facilitatory CA-releasing effect of Ach evoked by high-dose losartan (300 μM) was time-dependently depressed by pretreatment with nifedipine (Ca2+ channel blocker), while not by pretreatment with sodium nitroprusside (an NO donor). High-dose olmesartan (150 ∼ 600 μM), one of ARBs, also potentiated Ach-evoked CA release in time-dependent fashion. However, in the simultaneous presence of losartan (300 μM) and CGP42112 (an AT2 receptor agonist), the facilitatory responses of losartan on the CA secretion evoked by ACh were rather significantly reduced in comparison with that of losartan-treatment alone. Conclusion: Conclusively, these results demonstrate that high-dose losartan can potentiate the adrenomedullary CA secretion in a calcium-dependent fashion. It seems that this facilitatory effect of high-dose losartan may be mediated by activation of the Ca2+ influx through L-type Ca2+ channels into adrenomedullary cells without inhibition of NO synthesis, which seems to be relevant to AT2 receptor blockade. It also suggests that high-dose ARBs may be a risk factor in causing hypertensive response.

HIGH-DOSES OF LOSARTAN RATHER ACCELERATE THE SECRETION OF ADRENAL CATECHOLAMINES

Objective: Previously, we have found that Losartan (5∼50 microM), an AT1 receptor blocker, dose-dependently inhibits secretion of catecholamines (CA) evoked by cholinergic and angiotensin II (Ang II) receptor stimulation from the perfused rat adrenal medulla. The aim of the present study was to examine the characteristic effects of high-dose losartan on the CA secretion from the isolated perfused rat adrenal gland, and also to establish its mechanism of action. Design and method: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: The perfusion of high-dose losartan (150 ∼ 600 microM) into an adrenal vein for 90 min resulted in great increases in CA secretions evoked by acetylcholine in a dose-dependent fashion. Also, losartan (300 microM) enhanced the CA release evoked by Ang II, high K+ and DMPP (a selective nicotinic receptor agonist), McN-A-343 (a selective muscarinic M1 receptor agonist). Also, in the presence of losartan (300 microM), the CA secretory responses to veratridine (a selective Na+ channel activator), Bay-K-8644 (a Ca2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor) were significantly potentiated, respectively. The facilitatory CA-releasing effect of Ach evoked by high-dose losartan (300 microM) was time-dependently depressed by pretreatment with nifedipine (Ca2+ channel blocker), while not by pretreatment with sodium nitroprusside (an NO donor). High-dose olmesartan (150 ∼ 600 microM), one of ARBs, also potentiated Ach-evoked CA release in time-dependent fashion. However, in the simultaneous presence of losartan (300 microM) and CGP42112 (an AT2 receptor agonist), the facilitatory responses of losartan on the CA secretion evoked by ACh were rather significantly reduced in comparison with that of losartan-treatment alone. Conclusions: Conclusively, these results demonstrate that high-dose losartan can potentiate the adrenomedullary CA secretion in a calcium-dependent fashion. It seems that this facilitatory effect of high-dose losartan may be mediated by activation of the Ca2+ influx through L-type Ca2+ channels into adrenomedullary cells without inhibition of NO synthesis, which seems to be relevant to AT2 receptor blockade. It also suggests that high-dose ARBs may be a risk factor in causing hypertensive response.

PS 07-04 COMPARISON OF INHIBITORY EFFECTS BETWEEN GINSENOSIDE-Rb2 AND Rg2 ON ADRENAL CATECHOLAMINE RELEASE

Objective: The present study was attempted to compare ginsenoside-Rb2 (Rb2) one of panaxadiol saponins with Ginsenoside-Rg2 (Rg2), another panaxadiol saponin in the inhibitory effects on the secretion of catecholamines (CA) from the perfused model of the rat adrenal gland. Design and Method: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: Both Rb2 and Rg2 during perfusion into an adrenal vein for 90 min inhibited the CA release evoked by ACh, angiotensin II, DMPP, high K+, and McN-A-343 in a time-dependent manner. Also, in the presence of Rb2 or Rg2, the CA release evoked by veratridine (an activator of voltage-dependent Na+ channels), Bay-K-8644 (a voltage-dependent L-type Ca2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor) were significantly reduced. Both two ginsenosides also greatly induced NO release from adrenal medulla. Based on the same concentration of Rb2 and Rg2, for the CA release evoked by ACh, high K+, DMPP, McN-A-343, Ang II, veratridine, Bay-K-8644 and cyclopiazonic acid, as well as for No release, the following rank order of inhibitory potency was obtained: Rg2> Rb2. In the simultaneous presence of fimasartan, an antagonist of angiotensin II receptors and Ginsenoside-Rg2, ACh- or angiotensin II-evoked CA secretion was more strongly inhibited compared with that of fimasartan- or Rg2-treated alone. Conclusions: Collectively, these results demonstrate that both Rb2 and Rg2 can inhibit the CA secretion evoked by activation of both cholinergic and AT1 receptors stimulation from the perfused rat adrenal medulla. When these two ginsenosides were used in combination with a different antihypertensive agent, antihypertensive effects were enhanced, which may also be of clinical benefit. Based on concentrations used in this study, the inhibitory effect of ginsenoside-Rg2 on the CA secretion seems to be more potent than that of ginsenoside-Rb2.

Gintonin facilitates catecholamine secretion from the perfused adrenal medulla.

The present study was designed to investigate the characteristics of gintonin, one of components isolated from Korean Ginseng on secretion of catecholamines (CA) from the isolated perfused model of rat adrenal gland and to clarify its mechanism of action. Gintonin (1 to 30 µg/ml), perfused into an adrenal vein, markedly increased the CA secretion from the perfused rat adrenal medulla in a dose-dependent fashion. The gintonin-evoked CA secretion was greatly inhibited in the presence of chlorisondamine (1 µM, an autonomic ganglionic bloker), pirenzepine (2 µM, a muscarinic M1 receptor antagonist), Ki14625 (10 µM, an LPA1/3 receptor antagonist), amiloride (1 mM, an inhibitor of Na+/Ca2+ exchanger), a nicardipine (1 µM, a voltage-dependent Ca2+ channel blocker), TMB-8 (1 µM, an intracellular Ca2+ antagonist), and perfusion of Ca2+-free Krebs solution with 5mM EGTA (a Ca2+chelater), while was not affected by sodium nitroprusside (100 µM, a nitrosovasodialtor). Interestingly, LPA (0.3~3 µM, an LPA receptor agonist) also dose-dependently enhanced the CA secretion from the adrenal medulla, but this facilitatory effect of LPA was greatly inhibited in the presence of Ki 14625 (10 µM). Moreover, acetylcholine (AC)-evoked CA secretion was greatly potentiated during the perfusion of gintonin (3 µg/ml). Taken together, these results demonstrate the first evidence that gintonin increases the CA secretion from the perfused rat adrenal medulla in a dose-dependent fashion. This facilitatory effect of gintonin seems to be associated with activation of LPA- and cholinergic-receptors, which are relevant to the cytoplasmic Ca2+ increase by stimulation of the Ca2+ influx as well as by the inhibition of Ca2+ uptake into the cytoplasmic Ca2+ stores, without the increased nitric oxide (NO). Based on these results, it is thought that gintonin, one of ginseng components, can elevate the CA secretion from adrenal medulla by regulating the Ca2+ mobilization for exocytosis, suggesting facilitation of cardiovascular system. Also, these findings show that gintonin might be at least one of ginseng-induced hypertensive components.

Comparison of Inhibitory Effects between Enalapril and Losartan on Adrenal Catecholamine Secretion

❙ABSTRACT❙ Background: The present study was attempted to compare enalapril, an angiotensin-converting enzyme inhibitor with losartan an angiotensin II (Ang II) receptor blocker in the inhibitory effects on the secretion of catecholamines (CA) from the perfused model of the rat adrenal gland. Methods: The adrenal gland was isolated and perfused with Krebs-bicarbonate. CA was measured directly by using the fluorospectrophotometer. Results: Both enalapril and losartan during perfusion into an adrenal vein for 90 minutes inhibited the CA release evoked by acetylcholine (ACh), 1.1-dimethyl-4-phenyl piperazinium (DMPP, a selective Nn agonist), high K + (a direct membrane-depolarizer), 3-(m-chloro-phenyl-carbamoyl-oxy-2-butynyl- trimethyl ammonium (McN-A-343, a selective M1 agonist), and Ang II in a time-dependent manner. Also, in the presence of enalapril or losartan, the CA release evoked by veratridine (an activator of voltage-dependent Na + channels), 6-dimethyl-3-nitro-4-(2-trifluoromethyl phenyl)-pyridine-5-carboxylate (BAY-K-8644, an L-type Ca - 2+ channel activator), and cyclopiazonic acid (a cytoplasmic Ca 2+ -ATPase inhibitor) were significantly reduced. Based on the same concentration of enalapril and losartan, for the CA release evoked by ACh, high K + , DMPP, McN-A-343, Ang II, veratridine, BAY-K-8644, and cyclopiazonic acid, the following rank order of inhibitory potency was obtained: losartan > enalapril. In the simultaneous presence of enalapril and losartan, ACh-evoked CA secretion was more strongly inhibited compared with that of enalapril- or losartan-treated alone. Conclusions: Collectively, these results demonstrate that both enalapril and losartan inhibit the CA secretion evoked by activation of both cholinergic and Ang II type-1 receptors stimulation in the perfused rat adrenal medulla. When these two drugs were used in combination, their effects were enhanced, which may also be of clinical benefit. Based on concentration used in this study, the inhibitory effect of losartan on the CA secretion seems to be more potent than that of enalapril. (J Korean Soc Hypertens 2014;20(2):51-67)

Inhibitory effects of ginsenoside-rb2 on nicotinic stimulation-evoked catecholamine secretion.

The aim of the present study was to investigate whether ginsenoside-Rb2 (Rb2) can affect the secretion of catecholamines (CA) in the perfused model of the rat adrenal medulla. Rb2 (3~30 µM), perfused into an adrenal vein for 90 min, inhibited ACh (5.32 mM)-evoked CA secretory response in a dose- and time-dependent fashion. Rb2 (10 µM) also time-dependently inhibited the CA secretion evoked by DMPP (100 µM, a selective neuronal nicotinic receptor agonist) and high K+ (56 mM, a direct membrane depolarizer). Rb2 itself did not affect basal CA secretion (data not shown). Also, in the presence of Rb2 (50 µg/mL), the secretory responses of CA evoked by veratridine (a selective Na+ channel activator (50 µM), Bay-K-8644 (an L-type dihydropyridine Ca2+ channel activator, 10 µM), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor, 10 µM) were significantly reduced, respectively. Interestingly, in the simultaneous presence of Rb2 (10 µM) and L-NAME (an inhibitor of NO synthase, 30 µM), the inhibitory responses of Rb2 on ACh-evoked CA secretory response was considerably recovered to the extent of the corresponding control secretion compared with the inhibitory effect of Rb2-treatment alone. Practically, the level of NO released from adrenal medulla after the treatment of Rb2 (10 µM) was greatly elevated compared to the corresponding basal released level. Collectively, these results demonstrate that Rb2 inhibits the CA secretory responses evoked by nicotinic stimulation as well as by direct membrane-depolarization from the isolated perfused rat adrenal medulla. It seems that this inhibitory effect of Rb2 is mediated by inhibiting both the influx of Ca2+ and Na+ into the adrenomedullary chromaffin cells and also by suppressing the release of Ca2+ from the cytoplasmic calcium store, at least partly through the increased NO production due to the activation of nitric oxide synthase, which is relevant to neuronal nicotinic receptor blockade.

Influence of PD 123319 (AT2-Receptor Antagonist) on Catecholamine Secretion in the Perfused Rat Adrenal Medulla

Soon-Pyo Hong, MD, Bhandary Bidur, MD, Mee-Sung Choi, MD, Young-Hwan Seo, MD, Dong-Yoon Lim, MD Division of Cardiology, Departments of Internal Medicine, Pharmacology, Chosun University School of Medicine, Gwangju; Division of Sport Physiology, Department of Leasure and Soport, Dongshin University College of Public Health and Welfare, Naju; Department of Physical Education, Chosun University Graduate School, Gwangju, Korea 3)

276 COMPARISON OF INHIBITORY EFFECTS BETWEEN LOSARTAN, OLMESARTAN AND FIMASARTAN ON CATECHOLAMINE RELEASE IN THE PERFUSED ADRENAL MEDULLA

Recently, we have found that both losartan (Noh et al. 2009) and olmesartan (Lim et al., 2010) inhibit the secretion of catecholamines (CA) from the perfused rat adrenal medulla. Therefore, the aim of the present study was to compare the inhibitory effects of three major ARBs (losartan, olmesartan and fimasartan) each other on the CA release from the isolated perfused model of the rat adrenal medulla. Losartan (LST, 15 μM), olmesartan (OST, 15 μM) and fimasartan (FST, 15 μM), perfused into an adrenal vein for 90 min, inhibited the CA secretory responses evoked by ACh (5.32 mM) and high K+ (56 mM, a direct membrane depolarizer), DMPP (100 μM, a selective neuronal nicotinic receptor agonist) and McN-A-343 (100 μM, a selective muscarinic M1 receptor agonist) in a time-dependent fashion, respectively. Also, in adrenal glands loaded with LST (15 μM), OST (15 μM) and FST (15 μM), the CA secretory responses evoked by Bay-K-8644 (10 μM, an activator of L-type Ca2+ channels), cyclopiazonic acid (10 μM, an inhibitor of cytoplasmic Ca2+-ATPase), and veratridine (100 μM, an activator of voltage-dependent Na+ channels) as well as by angiotensin ll (100 nM) were time-dependently reduced, respectively. Based on the same concentration (15 μM) of three ARBs, for the CA release evoked by Ach, high K+, DMPP, and McN-A-343, the following rank order of inhibitory potency was obtained: LST<OST<FST. Also, for the CA release evoked by Bay-K-8644, cyclopiazonic acid, and angiotensin ll, the following rank order of inhibitory potency was obtained: LST<OST<FST. However, for the CA release evoked by veratridine, the following rank order of inhibitory potency was obtained: LST<OST=FST. All three ARBs themselves did not affect basal CA output. Collectively, these experimental results suggest that all three ARBs inhibit the CA secretion evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) as well as direct membrane depolarization from the perfused rat adrenal medulla. It seems that this inhibitory effect of all three ARBs may be mediated by blocking the influx of both Na+ and Ca2+ through their voltage-dependent ion channels into the adrenomedullary chromaffin cells as well as by inhibiting the Ca2+ release from its cytoplasmic calcium store. Based on the same concentration used in this study, it is also suggested that there is difference in potency of the inhibitory effects on the CA release between three ARBs, indicating that fimasartan seems to be more potent among three ARBs.

203 INFLUENCE OF SELF-FERMENTED PINE NEEDLE FRACTIONS ON CATECHOLAMINE RELEASE FROM THE RAT ADRENAL MEDULLA

Previously, we have found that self-fermented pine needle (Pinus densiflora) extract inhibits secretion of catecholamines (CA) from the perfused rat adrenal medulla (Shin & Lim, 2010), and also the contractile responses of isolated rat aortic strips induced by phenylephrine and high K+ (Yu et al., 2009). Therefore, the aim of the present study was to investigate the effects of several fractions obtained from methylene chloride (CH2Cl2) extract of self-fermented pine needle on the acetylcholine (ACh)-evoked CA release from the isolated perfused model of the rat adrenal medulla and to establish the mechanism of the most active fraction (Fr.)-induced inhibitory action on the CA release. We obtained 6 fractions from CH2Cl2 extract of self-fermented pine needle. For the ACh (5.32 mM)-evoked CA release, the following rank order of inhibitory potency was obtained: Fr.4>Fr.8-11>>Fr.3>Fr.6=Fr.7>Fr.1.2. Fr.4 (60 μg/mL) perfused into an adrenal vein for 90 min produced relatively time-dependent inhibition of the CA secretory responses to ACh (5.32 mM), high K+ (56 mM), DMPP (100 μM) and McN-A-343 (100 μM). Fr.4 itself did not affect basal CA secretion (data not shown). Also, in the presence of Fr.4 (60 μg/mL), the CA secretory responses to angiotensin II (AngII, 0.1 μM), veratridine (a selective Na+ channel activator, 10 μM), Bay-K-8644 (a L-type dihydropyridine Ca2+ channel activator, 10 μM), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor, 10 μM) were significantly reduced, respectively. In the simultaneous presence of Fr.4 (60 μg/mL) and L-NAME (an inhibitor of NO synthase, 30 μM), the inhibitory responses of Fr.4 on the CA secretion evoked by ACh, high K+, DMPP, McN-A-343, Bay-K-8644, cyclopiazonic acid, AngII and veratridine were considerably recovered to the extent of the corresponding control secretion compared with that of Fr.4-treatment alone. The level of NO released from adrenal medulla after the treatment of Fr.4 (60 μg/mL) was greatly elevated compared with the basal level. Taken together, these results demonstrate that Fr.4 inhibits the CA secretion from the isolated perfused rat adrenal medulla evoked by stimulation of cholinergic receptors as well as by direct membrane-depolarization. It seems that this inhibitory effect of Fr.4 is mediated by blocking the influx of Ca2+ and Na+ into the adrenomedullary chromaffin cells as well as by inhibition of Ca2+ release from the cytoplasmic calcium store, which is evoked at least partly through the increased NO production due to the activation of NO synthase. Based on these results, it is also thought that Fr. 4 isolated from CH2Cl2 extract of pine needle may contain beneficial antihypertensive components to prevent or treat hypertension.

Identification and Role of Muscarinic Receptor Subtypes Expressed in Rat Adrenal Medullary Cells

The muscarinic receptor is known to be involved in the acetylcholine (ACh)-induced secretion of catecholamines in the adrenal medullary (AM) cells of various mammals. The muscarinic receptor subtype involved and its physiological role, however, have not been elucidated yet. Thus, we investigated these issues in acutely isolated rat AM cells and perfused rat adrenal medulla. The RT-PCR analysis revealed the presence of M(2), M(3), M(4), and M(5) mRNAs. Immunocytochemistry with specific antibodies showed that M(5)-like immunoreactivities (IRs) were detected at half the cell membrane area, which was much larger than that with M(3)- or M(4)-like IRs. Muscarine produced inward currents in a dose-dependent manner. Pilocarpine, McN-A-343, and oxotremorine were less efficient than muscarine; and RS-86, which has no action on the M(5) receptor, produced no current. Electrical stimulation of nerve fibers produced a frequency-dependent increase in the Ca(2+) signal in perfused adrenal medullae. Muscarinic receptors were found to be involved in neuronal transmission in AM cells in the presence of a cholinesterase inhibitor, which suppresses ACh degradation. We concluded that the M(5) receptor is the major muscarinic receptor subtype in rat AM cells and may be involved in neuronal transmission under conditions where ACh spills over the synapse.

Inhibitory Effects of Olmesartan on Catecholamine Secretion from the Perfused Rat Adrenal Medulla

The present sutdy aimed to determine whether olmesartan, an angiotensin II (Ang II) type 1 (AT(1)) receptor blocker, can influence the CA release from the isolated perfused model of the rat adrenal medulla. Olmesartan (5~50 µM) perfused into an adrenal vein for 90 min produced dose- and time-dependent inhibition of the CA secretory responses evoked by ACh (5.32 mM), high K(+) (56 mM, a direct membrane-depolarizer), DMPP (100 µM) and McN-A-343 (100 µM). Olmesartan did not affect basal CA secretion. Also, in adrenal glands loaded with olmesartan (15 µM), the CA secretory responses evoked by Bay-K-8644 (10 µM, an activator of voltage-dependent L-type Ca(2+) channels), cyclopiazonic acid (10 µM, an inhibitor of cytoplasmic Ca(2+) -ATPase), veratridine (100 µM, an activator of voltage-dependent Na(+) channels), and Ang II (100 nM) were markedly inhibited. However, at high concentrations (150~300 µM), olmesartan rather enhanced the ACh-evoked CA secretion. Taken together, these results show that olmesartan at low concentrations inhibits the CA secretion evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) as well as by direct membrane depolarization from the rat adrenal medulla, but at high concentrations it rather potentiates the ACh-evoked CA secretion. It seems that olmesartan has a dual action, acting as both agonist and antagonist at nicotinic receptors of the isolated perfused rat adrenal medulla, which might be dependent on the concentration. It is also thought that this inhibitory effect of olmesartan may be mediated by blocking the influx of both Na(+) and Ca(2+) into the rat adrenomedullary chromaffin cells as well as by inhibiting the Ca(2+) release from the cytoplasmic calcium store, which is thought to be relevant to the AT(1) receptor blockade, in addition to its enhancement on the CA secreton.

Inhibitory effect of methylene chloride fraction extracted from Rubus coreanum on catecholamine secretion from the perfused rat adrenal medulla

Inhibitory effect of methylene chloride fraction extracted from Rubus coreanum on catecholamine secretion from the perfused rat adrenal medulla

The effects of enalapril and losartan on catecholamine release in the perfused rat adrenal medulla

The effects of enalapril and losartan on catecholamine release in the perfused rat adrenal medulla

Provinol inhibits catecholamine secretion from the rat adrenal medulla.

The aim of the present study was to examine the effect of provinol, which is a mixture of polyphenolic compounds from red wine, on the secretion of catecholamines (CA) from isolated perfused rat adrenal medulla, and to elucidate its mechanism of action. Provinol (0.3~3 microg/ml) perfused into an adrenal vein for 90 min dose- and time-dependently inhibited the CA secretory responses evoked by ACh (5.32 mM), high K(+) (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic N(N) receptor agonist, 100 microM) and McN-A-343 (a selective muscarinic M(1) receptor agonist, 100 microM). Provinol itself did not affect basal CA secretion. Also, in the presence of provinol (1 microg/ml), the secretory responses of CA evoked by Bay-K-8644 (a voltage-dependent L-type dihydropyridine Ca(2+) channel activator, 10 microM), cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10 microM) and veratridine (an activator of voltage-dependent Na(+) channels, 10 microM) were significantly reduced. Interestingly, in the simultaneous presence of provinol (1 microg/ml) plus L-NAME (a selective inhibitor of NO synthase, 30 microM), the CA secretory responses evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclpiazonic acid recovered to the considerable extent of the corresponding control secretion in comparison with the inhibition of provinol-treatment alone. Under the same condition, the level of NO released from adrenal medulla after the treatment of provinol (3 microg/ml) was greatly elevated in comparison to its basal release. Taken together, these data demonstrate that provinol inhibits the CA secretory responses evoked by stimulation of cholinergic (both muscarinic and nicotinic) receptors as well as by direct membrane-depolarization from the perfused rat adrenal medulla. This inhibitory effect of provinol seems to be exerted by inhibiting the influx of both calcium and sodium into the rat adrenal medullary cells along with the blockade of Ca(2+) release from the cytoplasmic calcium store at least partly through the increased NO production due to the activation of nitric oxide synthase.

Inhibitory Mechanism of Polyphenol Compounds Isolated from Red Wine on Catecholamine Release in the Perfused Rat Adrenal Medulla

Inhibitory Mechanism of Polyphenol Compounds Isolated from Red Wine on Catecholamine Release in the Perfused Rat Adrenal Medulla

Influence of ketamine on catecholamine secretion in the perfused rat adrenal medulla.

The aim of the present study was to examine the effects of ketamine, a dissociative anesthetics, on secretion of catecholamines (CA) secretion evoked by cholinergic stimulation from the perfused model of the isolated rat adrenal gland, and to establish its mechanism of action, and to compare ketamine effect with that of thiopental sodium, which is one of intravenous barbiturate anesthetics. Ketamine (30~300microM), perfused into an adrenal vein for 60 min, dose- and time-dependently inhibited the CA secretory responses evoked by ACh (5.32 mM), high K(+) (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic NN receptor agonist, 100microM) and McN-A-343 (a selective muscarinic M1 receptor agonist, 100microM). Also, in the presence of ketamine (100microM), the CA secretory responses evoked by veratridine (a voltage-dependent Na(+) channel activator, 100microM), Bay-K-8644 (an L-type dihydropyridine Ca(2+) channel activator, 10microM), and cyclopiazonic acid (a cytoplasmic Ca(2+)-ATPase inhibitor, 10microM) were significantly reduced, respectively. Interestingly, thiopental sodium (100microM) also caused the inhibitory effects on the CA secretory responses evoked by ACh, high K(+) , DMPP, McN-A-343, veratridine, Bay-K-8644, and cyclopiazonic acid. Collectively, these experimental results demonstrate that ketamine inhibits the CA secretion evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors and the membrane depolarization from the isolated perfused rat adrenal gland. It seems likely that the inhibitory effect of ketamine is mediated by blocking the influx of both Ca(2+) and Na(+) through voltage-dependent Ca(2+) and Na(+) channels into the rat adrenal medullary chromaffin cells as well as by inhibiting Ca(2+) release from the cytoplasmic calcium store, which are relevant to the blockade of cholinergic receptors. It is also thought that, on the basis of concentrations, ketamine causes similar inhibitory effect with thiopental in the CA secretion from the perfused rat adrenal medulla.

Influence of polyphenolic compounds isolated fromRubus coreanum on catecholamine release in the rat adrenal medulla

The aim of the present study was to investigate whether polyphenolic compounds isolated from wine brewed from Rubus coreanum MIQUEL (PCRC) may affect the release of catecholamine (CA) from the isolated perfused rat adrenal medulla, and to establish its mechanism of action. PCRC (20-180 microg/mL) perfused into an adrenal vein for 90 min dose- and time-dependently inhibited the CA secretory responses evoked by acetylcholine (ACh, 5.32 mM), high K+ (a direct membrane-depolarizer, 56 mM), DMPP (a selective neuronal nicotinic Nn receptor agonist, 100 microM) and McN-A-343 (a selective muscarinic M1 receptor agonist, 100 microM). Also, in the presence of PCRC (60 microg/mL), the secretory responses of CA evoked by Bay-K-8644 (a L-type dihydropyridine Ca2+ channel activator, 10 microM), and cyclopiazonic acid (a cytoplasmic Ca2+-ATPase inhibitor, 10 microM) were significantly reduced, respectively. In the simultaneous presence of PCRC (60 microg/mL) and L-NAME (an inhibitor of NO synthase, 30 microM), the inhibitory responses of PCRC on the CA secretion evoked by ACh, high K+, DMPP, and Bay-K-8644 were considerably recovered to the extent of the corresponding control secretion compared with the inhibitory effect of PCRC alone. Taken together, these results obtained from the present study demonstrate that PCRC inhibits the CA secretory responses from the isolated perfused adrenal gland of the normotensive rats evoked by stimulation of cholinergic (both muscarinic and nicotinic) receptors as well as by direct membrane-depolarization. It seems that this inhibitory effect of PCRC is exerted by inhibiting both the calcium influx into the rat adrenal medullary chromaffin cells and the uptake of Ca2+ into the cytoplasmic calcium store partly through the increased NO production due to the activation of nitric oxide synthase (NOS), which are at least relevant to the direct interaction with the nicotinic receptor itself. It is also thought that PCRC might be effective in prevention of cardiovascular disease.

CCCP enhances catecholamine release from the perfused rat adrenal medulla

The present study was designed to investigate the effect of carbonyl cyanide m-chlorophenylhydrazone (CCCP), a mitochondrial uncoupler, on secretion of catecholamines from the isolated perfused model of the rat adrenal gland and to establish the mechanism of its adrenomedullary secretion. The perfusion of CCCP (3 × 10 − 5 M) into an adrenal vein of for 90 min caused a great increase in catecholamine secretion. Tachyphylaxis to catecholamine-releasing effect of CCCP was not observed by repeated perfusion of it. The net catecholamine-releasing effects of CCCP were depressed by pretreament with pirenzepine (a selective muscarinic M 1-receptor antagonist), chlorisondamine (a selective neuronal nicotinic receptor antagonist), nicardipine (an L-type Ca 2+-channel antagonist), TMB-8 (an intracellular Ca 2+-antagonist), and the perfusion of EGTA plus Ca 2+-free medium, respectively. In the presence of CCCP (3 × 10 − 5 M), catecholamine secretory responses induced by ACh (5.32 × 10 − 3 M), high K + (5.6 × 10 − 2 M, a direct membrane depolarizer), DMPP (10 − 4 M, (a selective neuronal nicotinic receptor agonist), and McN-A-343 (10 − 4 M, (a selective muscarinic M 1-receptor agonist) were significantly enhanced. CCCP also significantly enhanced the catecholamine secretory responses evoked by Bay-K-8644 (10 − 5 M), L-type Ca 2+ channel activator, and cyclopiazonic acid (10 − 5 M), an inhibitor of Ca 2+-ATPase. Furthermore, the perfusion of FCCP (3 × 10 − 5 M), a similar mitochondrial uncoupler, into an adrenal vein of for 90 min also caused a great increase in catecholamine secretion in a similar pattern with CCCP. Taken together, the results demonstrate that CCCP causes the catecholamine secretion from the perfused rat adrenal medulla in a calcium-dependent fashion. It is thought that this catecholamine secretory enhancement of CCCP may be mediated by both cholinergic receptor stimulation and membrane depolarization, which are relevant to the cytoplasmic Ca 2+ increase by stimulation of the Ca 2+ influx as well as by the inhibition of Ca 2+ uptake into the cytoplasmic Ca 2+ stores (both endoplasmic reticulum and mitochondria in chromaffin cells). It also seems that protonophores, such as CCCP, suppress mitochondrial Ca 2+ uptake and increase the stimulated secretion of catecholamine by the secretagogues. These results indicate that mitochondria modulate catecholamine secretion by regulating the Ca 2+ mobilization for exocytosis.