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

Abstract

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.

Keywords: Adrenal medulla; Catecholamine secretion; Cholinergic receptors; Ketamine; thiopental.

Fig. 1

Concentration-dependent effects of ketamine on the secretory responses of catecholamines (CA) from the perfused rat adrenal glands evoked by acetylcholine (ACh, Upper) and by high K⁺ (Lower). CA secretion by a single injection of ACh (5.32×10^-3 M) or K⁺ (56 mM) in a volume of 0.05 ml was evoked at 15 min intervals after preloading with 30, 100 and 300 µM of ketamine, respectively, for 60 min as indicated at an arrow mark. Numbers in the parenthesis indicate number of rat adrenal glands. Vertical bars on the columns represent the standard error of the mean (S.E.M.). Ordinate: the amounts of CA secreted from the adrenal gland (% of control). Abscissa: collection time of perfusate (min). Statistical difference was obtained by comparing the corresponding control with each concentration-pretreated group of ketamine. Pefusates induced by ACh and high K⁺ were collected for 4 minutes, respectively. ^**p<0.01.

Fig. 2

Concentration-dependent effects of ketamine on the CA secretory responses evoked by DMPP (Upper) and McN-A-343 (Lower) from the perfused rat adrenal glands. The CA secretory responses by the perfusion of DMPP (10^-4 M) and McN-A-343 (10^-4 M) for 4 min at 20 and 15 min intervals were induced after preloading with 30, 100 and 300µM of ketamine for 60 min, respectively. Pefusates induced by DMPP and McN-A-343 were collected for 8 and 4 minutes, respectively. Other legends are the same as in Fig. 1. ^**P<0.01. ns: Statistically not significant.

Fig. 3

Time course effect of ketamine on the CA release evoked by Bay-K-8644 (Upper) and cyclopiazonic acid (Lower) from the perfused rat adrenal glands. Bay-K-8644 (10^-5 M) and cyclopiazonic acid (10^-5 M) were perfused into an adrenal vein for 4 min at 15 min intervals after preloading with 100µM of ketamine for 60 min, respectively. Other legends are the same as in Fig. 1. ^*P<0.05, ^**P<0.01. ns: Statistically not significant.

Fig. 4

Time course effect of ketamine on the CA release evoked by veratridine from the perfused rat adrenal glands. Veratridine (10^-4 M) was perfused into an adrenal vein for 4 min at 15 min intervals after preloading with 100µM of ketamine for 60 min. Other legends are the same as in Fig. 1. ^**P<0.01.

Fig. 5

Time course effect of of thiopental on the secretory responses of catecholamines (CA) from the perfused rat adrenal glands evoked by acetylcholine (ACh, Upper) and by high K⁺ (Lower). CA secretion by a single injection of ACh (5.32×10^-3 M) or K⁺ (56 mM) in a volume of 0.05 ml was evoked at 15 min intervals after preloading with 100µM thiopentall for 60 min as indicated at an arrow mark. Other legends are the same as in Fig. 1. ^**P<0.01.

Fig. 6

Time course effect of of thiopental on the CA secretory responses evoked by DMPP (Upper) and McN-A-343 (Lower) from the perfused rat adrenal glands. The CA secretory responses by the perfusion of DMPP (10^-4 M) and McN-A-343 (10^-4 M) for 4 min at 20 and 15 min intervals were induced after preloading with 100µM thiopental for 60 min, respectively. Other legends are the same as in Fig. 1. ^**P<0.01. ns: Statistically not significant.

Fig. 7

Time course effect of thiopental on the CA release evoked by Bay-K-8644 (Upper) and cyclopiazonic acid (Lower) from the perfused rat adrenal glands. Bay-K-8644 (10^-5 M) and cyclopiazonic acid (10^-5 M) were perfused into an adrenal vein for 4 min at 15 min intervals after preloading with 100µM of thiopental for 60 min, respectively. Other legends are the same as in Fig. 1. ^*P<0.05, ^**P<0.01. ns: Statistically not significant.

Fig. 8

Time course effect of thiopental on the CA release evoked by veratridine from the perfused rat adrenal glands. Veratridine (10^-4 M) was perfused into an adrenal vein for 4 min at 15 min intervals after preloading with 100µM of thiopental for 60 min. Other legends are the same as in Fig. 1. ^**P<0.01.