Influence of SKF81297 on Catecholamine Release from the Perfused Rat Adrenal Medulla

The aim of the present study was to investigate the effects of 6-chloro-7,8-dihydroxy-1-phenyl-2,3, 4,5-tetrahydro-1H-3-benzazepine (SKF81297), a selective agonist of dopaminergic D1 receptor, on the secretion of catecholamines (CA) evoked by cholinergic stimulation and membrane-depolarization in the isolated perfused rat adrenal gland, and also to elucidate the mechanism involved. SKF81297 (10~100microM) perfused into an adrenal vein for 60 min produced dose- and time-dependent inhibition of CA secretory responses evoked by ACh (5.32 mM), high K+ (56 mM), DMPP (100microM) and McN-A-343 (100microM). Also, in adrenal glands loaded with SKF81297 (30microM), the CA secretory responses evoked by Bay-K-8644 (10microM), an activator of L-type Ca2+ channels and cyclopiazonic acid (10microM), an inhibitor of cytoplasmic Ca2+-ATPase were also inhibited. However, in the presence of the dopamine D1 receptor antagonist, (R)-(+)-8-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-benzazepine-7-ol (SCH23390, 3microM), which is a selective antagonist of dopaminergic D1 receptor, the inhibitory responses of SKF81297 (30microM) on the CA secretion evoked by ACh, high K+, DMPP, McN-A-343, Bay-K-8644, and cyclopiazonic acid were significantly reduced. Collectively, these experimental results suggest that SKF81297 inhibits the CA secretion from the rat adrenal medulla evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) and membrane depolarization. This inhibitory of SKF81297 seems to be mediated by stimulation of dopaminergic D1 receptors located on the rat adrenomedullary chromaffin cells, which are relevant to extra- and intracellular calcium mobilization. Therefore, it is thought that the presence of the dopaminergic D1 receptors may be involved in regulation of CA release in the rat adrenal medulla.

Mechanism of Leptin-Induced Potentiation of Catecholamine Secretion Evoked by Cholinergic Stimulation in the Rat Adrenal Medulla

The aim of the present study was to examine the effect of leptin on CA release from the isolated perfused model of the rat adrenal gland, and to establish its mechanism of action. Leptin (1~100 ng/ml), when perfused into an adrenal vein of the rat adrenal gland for 60 min, enhanced a dose-dependently the secretory responses of CA evoked by ACh (5.32x10 (-3)M), DMPP (10 (-4)M) and McN-A-343 (10 (-4)M), although it alone has weak effect on CA secretion. However, it did not affect the CA secretion evoked by excess K+ (5.6x10 (-2)M). Leptin alone produced a weak secretory response of the CA. Moreover, leptin (10 ng/ml) in to an adrenal vein for 60 min also augmented the CA release evoked by BAY-K-8644, an activator of the dihydropyridine L-type Ca2+ channels, and cyclopiazonic acid, an inhibitor of cytoplasmic Ca2+ ATPase. However, in the presence of U0126 (1micrometer), an inhibitor of mitogen-activated protein kinase (MAPK), leptin no longer enhanced the CA secretion evoked by ACh and DMPP. Furthermore, in the presence of anti-leptin (10 ng/ml), an antagonist of Ob receptor, leptin (10 ng/ml) also no longer potentiated the CA secretory responses evoked by DMPP and Bay-K-8644. Collectively, these experimental results suggest that leptin enhances the CA secretion from the rat adrenal medulla evoked by cholinergic stimulation (both nicotininc and muscarinic receptors), but does not that by membrane depolarization. It seems that this enhanced effect of leptin may be mediated by activation of U0126-sensitive MAPK through the leptin receptors, which is probably relevant to the activation of the dihydropyridine L-type Ca2+ channels located on the rat adrenomedullary chromaffin cells.

Influence of Bradykinin on Catecholamine Release from the Rat Adrenal Medulla

The present study was undertaken to investigate the effect of bradykinin on secretion of catecholamines (CA) evoked by stimulation of cholinergic receptors and membrane depolarization from the isolated perfused model of the rat adrenal glands, and to elucidate its mechanism of action. Bradykinin (3 X 10 (-8) M) alone produced a weak secretory response of the CA. however, the perfusion with bradykinin (3 X 10 (-8) M) into an adrenal vein of the rat adrenal gland for 90 min enhanced markedly the secretory responses of CA evoked by ACh (5.32 X 10 (-3) M), excess K+ (5.6 X 10 (-2) M, a membrane depolarizer), DMPP (10 (-4) M, a selective neuronal nicotinic agonist) and McN-A-343 (10 (-4) M, a selective M1-muscarinic agonist). Moreover, bradykinin (3 X 10 (-8) M) in to an adrenal vein for 90 min also augmented the CA release evoked by BAY-K-8644, an activator of the dihydropyridine L-type Ca2+ channels. However, in the presence of (N-Methyl-D-Phe7) -bradykinin trifluoroacetate salt (3 X 10 (-8) M), an antagonist of BK2-bradykinin receptor, bradykinin no longer enhanced the CA secretion evoked by Ach and high potassium whereas the pretreatment with Lys- (des-Arg9, Leu8) -bradykinin trifluoroacetate salt (3 X 10 (-8) M), an antagonist of BK1-bradykinin receptor did fail to affect them. Furthermore, the perfusion with bradykinin (3 X 10 (-6) M) into an adrenal vein of the rabbit adrenal gland for 90 min enhanced markedly the secretory responses of CA evoked by excess K+ (5.6 X 10 (-2) M). Collectively, these experimental results suggest that bradykinin enhances the CA secretion from the rat adrenal medulla evoked by cholinergic stimulation (both nicotininc and muscarinic receptors) and membrane depolarization through the activation of B2-bradykinin receptors, not through B1-bradykinin receptors. This facilitatory effect of bradykinin seems to be associated to the increased Ca2+ influx through the activation of the dihydropyridine L-type Ca2+ channels.