Roles of dopaminergic d(1) and d(2) receptors in catecholamine release from the rat adrenal medulla

Abstract

The aim of the present study was designed to establish comparatively the inhibitory effects of D(1)-like and D(2)-like dopaminergic receptor agonists, SKF81297 and R(-)-TNPA on the release of catecholamines (CA) evoked by cholinergic stimulation and membrane depolarization from the isolated perfused model of the rat adrenal medulla. SKF81297 (30microM) and R-(-)-TNPA (30microM) perfused into an adrenal vein for 60 min, produced great inhibition in the CA secretory responses evoked by ACh (5.32x10(- 3) M), DMPP (10(-4) M), McN-A-343 (10(-4) M), high K(+) (5.6x10(-2) M), Bay-K-8644 (10microM), and cyclopiazonic acid (10microM), respectively. For the release of CA evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid, the following rank order of inhibitory potency was obtained: SKF81297>R-(-)-TNPA. However, R(+)-SCH23390, a selectve D(1)-like dopaminergic receptor antagonist, and S(-)-raclopride, a selectve D(2)-like dopaminergic receptor antagonist, enhanced the CA secretory responses evoked by ACh, high K(+), DMPP, McN-A-343, Bay-K-8644 and cyclopiazonic acid only for 0~4 min. The rank order for the enhancement of CA release evoked by high K(+), McN-A-343 and cyclopiazonic acid was R(+)-SCH23390>S(-)-raclopride. Also, the rank order for ACh, DMPP and Bay-K-8644 was S(-)-raclopride > R(+)-SCH23390. Taken together, these results demonstrate that both SKF81297 and R-(-)-TNPA inhibit the CA release evoked by stimulation of cholinergic (both nicotinic and muscarinic) receptors and the membrane depolarization from the isolated perfused rat adrenal gland without affecting the basal release, respectively, but both R(+)-SCH23390 and S(-)-raclopride facilitate the CA release evoked by them. It seems likely that the inhibitory effects of SKF81297 and R-(-)-TNPA are mediated by the activation of D(1)-like and D(2)-like dopaminergic receptors located on the rat adrenomedullary chromaffin cells, respectively, whereas the facilitatory effects of R(+)-SCH23390 and S(-)-raclopride are mediated by the blockade of D(1)-like and D(2)-like dopaminergic receptors, respectively: this action is possibly associated with extra- and intracellular calcium mobilization. Based on these results, it is thought that the presence of dopaminergic D(1) receptors may play an important role in regulation of the rat adrenomedullary CA secretion, in addition to well-known dopaminergic D(2) receptors.

Keywords: Adrenal meduula; Catecholamine secretion; Dopaminergic receptors; R(+)-SCH23390; R-(-)TNPA; S(-)-raclopride; SKF81297.

Fig. 1

Time course effect of SKF81297 (SKF) and R-(-)TNPA(TNPA) on the secretory responses of catecholamines (CA) from the isolated 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 30µM of SKF or TNPA 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 (CONT) with each concentration-pretreated group of SKF81297. Pefusates induced by ACh and high K⁺ were collected for 4 minutes, respectively. ^*p<0.05, ^**p<0.01. ns: Statistically not significant.

Fig. 2

Time course effect of SKF81297 (SKF) and R-(-)TNPA(TNPA) on the CA secretory responses from the isolated perfused rat adrenal glands evoked by DMPP (Upper) and McN-A-343 (Lower). The CA secretory responses by the perfusion of DMPP (10^-4 M) and McN-A-343 (10^-4 M) for 2 min at 20 and 15 min intervals were induced after preloading with 30µM of SKF or TNPA 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<0.05, ^**p<0.01. ns: Statistically not significant.

Fig. 3

Time course effect of SKF81297 (SKF) and R-(-)TNPA(TNPA) on the CA release from the rat adrenal glands evoked by Bay-K-8644 (Upper) and cyclopiazonic acid (Lower). 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 30µM of SKF or TNPA 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 R(+)-SCH23390 (SCH) and S(-)-raclopride (RAC) on the CA release evoked from the isolated perfused rat adrenal glands by acetylcholine (Upper) and high K⁺ (Lower). CA secretion by a single injection of Ach (5.32×10^-3 M) or high K⁺ (5.6×10^-2 M) was induced "BEFORE (CONTROL)" and " AFTER" preloading simultaneously with 3µM SCH or 3µM RAC for 60 min, respectively. Other legends are the same as in Fig. 1. ^*p<0.05, ^**p<0.01. ns: Statistically not significant.

Fig. 5

Time course effect of R(+)-SCH23390 (SCH) and S(-)-raclopride (RAC) on the CA release from the isolated perfused rat adrenal glands evoked by DMPP (Upper) and McN-A-343 (Lower). The CA secretory responses by the perfusion of DMPP (10^-4 M) and McN-A-343 (10^-4 M) for 2 min and 4 min at 20 and 15 min intervals were induced "BEFORE (CONTROL)" and "AFTER" preloading simultaneously with 3µM SCH or 3µM RAC for 60 min, respectively. Other legends are the same as in Fig. 1. ^*p<0.05, ^**p<0.01. ns: Statistically not significant.

Fig. 6

Time course effect of R(+)-SCH23390 (SCH) and S(-)-raclopride (RAC) on the CA release evoked by Bay-K-8644 (Upper) and cyclopiazonic acid (Lower) from the 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 "BEFORE (CONTROL)" and " AFTER" preloading simultaneously with 3µM SCH or 3µM RAC for 60 min, respectively. Other legends are the same as in Fig. 1. ^**p<0.01. ns: Statistically not significant.