Effect of Doxorubicin on Catecholamine Release in the Isolated Perfused Rat Adrenal Gland

The present study was undertaken to investigate the effect of doxorubicin (DX) on secretion of catecholamines (CA) evoked by ACh, high K+, DMPP and McN-A-343 from the isolated perfused rat adrenal gland and to establish the mechanism of its action. DX (10(-7)~10(-6) M) perfused into an adrenal vein for 60 min produced relatively dose- and time-dependent inhibition of CA secretory responses evoked by ACh (5.32 X 10(-3) M), DMPP (10(-4) M) and McN-A-343 (10(-4) M). However, lower dose of DX did not affect CA secretion by high K+ (5.6 X 10(-2) M), but its higher doses depressed time-dependently CA secretion evoked by high K+. DX itself did also fail to affect basal CA output. In adrenal glands loaded with DX (3 X 10(-7) M), CA secretory responses evoked by Bay-K-8644, an activator of L-type Ca2+ channels and cyclopiazonic acid, an inhibitor of cytoplasmic Ca2+-ATPase were time-dependently inhibited. Furthermore, daunorubicin (3 X 10(-7) M), given into the adrenal gland for 60 min, attenuated CA secretory responses evoked by ACh, high K+, DMPP and McN-A-343. Taken together, these results suggest that DX causes relatively dose- and time-dependent inhibition of CA secretory responses evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors from the isolated perfused rat adrenal gland. However, lower dose of DX did not affect CA secretion by high K+, and higher doses of DX reduced time-dependently CA secretion of high K+. It is thought that these effects of DX may be mediated by inhibiting both influx of extracellular calcium into the rat adrenomedullary chromaffin cells and intracelluar calcium release from the cytoplasmic store. Also, there was no difference in the mode of action between DX and daunorubicin in rat adrenomedullary CA secretion.

Mechanism of epibatidine-induced catecholamine secretion in the rat adrenal gland

The present study was attempted to investigate the characteristics of epibatidine on secretion of catecholamines (CA) from the isolated perfused model of the rat adrenal gland, and to establish the mechanism of action. Epibatidine (3X10(-8) M) injected into an adrenal vein produced a great inhibition in secretory response of CA from the perfused rat adrenal gland. However, upon the repeated injection of epibatidine (3X10(-8) M) at 15 min-intervals, CA secretion was rapidly decreased after second injection of epibatidine. However, there was no statistical difference between CA secretory responses of both 1st and 2nd periods by the successive administration of epibatidine at 120 min-intervals. Tachyphylaxis to releasing effects of CA evoked by epibatidine was observed by the repeated administration. Therefore, in all subsequent experiments, epibatidine was not administered successively more than twice only 120 min-intervals. The epibatidine-induced CA secretion was markedly inhibited by the pretreatment with atropine, chlorisondamine, pirenzepine, nicardipine, TMB-8, and perfusion of Ca2+/-free Krebs solution containing EGTA, while was not affected by diphenhydramine. Moreover, the CA secretion evoked by ACh for 1st period (0apprx4 min) was greatly potentiated by the simultaneous perfusion of epibatidine (1.5X10(-8) M), but followed by time-dependently gradual reduction after 2nd period. The CA release evoked by high potassium (5.6+/-10(-8) M) for 1st period (0apprx4 min) was also enhanced by the simultaneous perfusion of epibatidine, but those after 2nd period were not affected. Taken together, these experimental data suggest that epibatidine causes catecholamine secretion in a calcium dependent fashion from the perfused rat adrenal gland through activation of neuronal cholinergic (nicotinic and muscarinic) receptors located in adrenomedullary chromaffin cells. It also seems that epibatidine-evoked catecholamine release is not relevant to stimulation of histaminergic receptors.

Influence of strychnine on catecholamine release evoked by activation of cholinergic receptors from the perfused rat adrenal gland

The present study was attempted to investigate the effect of strychnine on catecholamine (CA) secretion evoked by ACh, high K+, DMPP and McN-A-343 from the isolated perfused rat adrenal gland. The perfusion of strychnine (10-4 M) into an adrenal vein for 20 min produced great inhibition in CA secretory responses evoked by ACh (5.32X10-3 M), DMPP (10-4 M for 2 min) and McN-A-343 (10-4 M for 2 min), but did not alter CA secretion by high K+ (5.6X10-2 M). Strychnine itself did also fail to affect basal catecholamine output. Furthermore, in adrenal glands preloaded simultaneously with strychnine (10-4 M) and glycine (an agonist of glycinergic receptor, 10-4 M), CA secretory responses evoked by ACh, DMPP and McN-A-343 were considerably recovered to some extent when compared with those evoked by treatment with strychnine only. However, CA secretion by high K+ (5.6X10-2 M) was not affected. Taken together, these results demonstrate that strychnine inhibits greatly the CA secretory responses evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors, but does not affect that by membrane depolarization. It is suggested that strychnine-sensitive glycinergic receptors are localized in rat adrenal medullary chromaffin cells.

Mechanism of vasoactive intestinal polypeptide-induced catecholamine secretion from the rat adrenal medulla

The present study was attempted to investigate the effect of vasoactive intestinal polypeptide (VIP) on secretion of catecholamines (CA) and to establish whether there is the existence of a noncholinergic mechanism in adrenomedullary CA secretion from the isolated perfused rat adrenal gland. The perfusion into an adrenal vein of VIP (3 X 10-6 M) for 5 min or the injection of acetylcholine (ACh, 5.32 X 10-3 M) resulted in great increases in CA secretion. Tachyphylaxis to releasing effect of CA evoked by VIP was not observed by the repeated perfusion. The net increase in adrenal CA secretion evoked by VIP still remained unaffected in the presence of atropine or chlorisondamine. However, the CA release in response to ACh was greatly inhibited by the pretreatment with atropine or chlorisondamine. The releasing effects of CA evoked by either VIP or ACh were depressed by pretreatment with nicardipine, TMB-8, and the perfusion of Ca2+-free medium. Moreover, VIP- as well as ACh-evoked CA secretory responses were markedly inhibited under the presence of (Lys1, Pro2.5, Arg3.4, Tyr6)-VIP or naloxone. CA secretory responses induced by ACh and high K+ (5.6 X 10-2 M) were potentiated by infusion of VIP (3 X 10-6 M for 5 min). Taken together, these experimental results indicate that VIP causes CA release in a fashion of calcium ion-dependence, suggesting strongly that there exists a noncholinergic mechanism that may be involved in the regulation of adrenomedullary CA secretion through VIP receptors in the rat adrenal gland, and that VIP may be the noncholinergic excitatory secretagogue present in the chromaffin cells.