mohammed benyamina

The effect of cholinergic agonists on glucocorticoid

and mineralocorticoid production by frog interrenal

(adrenal) tissue was studied in vitro by means of

continuous perifusion. Acetylcholine, at doses ranging

from 1 to 100 \g=m\mol/l,stimulated both corticosterone

and aldosterone output in a dose-dependent manner,

with a half-maximal effective dose of 2\m=.\5 \g=m\mol/l.

Corticosteroid production was also stimulated by

muscarine (10 \g=m\mol/l).In contrast, neither nicotine

nor nicotine bitartrate (1\p=n-\100 \g=m\mol/l)enhanced corticosteroid

biosynthesis. The kinetics of the response of

adrenal cells to acetylcholine and muscarine were

similar to those observed during angiotensin II stimulation.

In particular, a significant reduction (20\p=n-\40%)

in the spontaneous level of corticosteroid production

was recorded after the initial infusion of muscarinic

agents, but no further decrease in the basal level

occurred after a second cholinergic administration.

The effect of acetylcholine was blocked by the

muscarinic receptor antagonist atropine (10 \g=m\mol/l).

These results indicate that acetylcholine can stimulate

frog adrenocortical cells through muscarinic receptors.

Repeated 20-min pulses of acetylcholine (50 \g=m\mol/l)or

muscarine (10 \g=m\mol/l),given at one pulse per 130 min,

resulted in a marked reduction in the secretory response

to the second pulse. No reduction in the stimulatory

effect of acetylcholine or muscarine was observed when

a 6\m=.\5-h interval separated two 20-min infusions of the

secretagogue. In contrast with these findings, iterative

pulses of the muscarinic agonist pilocarpine (in the

range 1\p=n-\100 \g=m\mol/l)did not cause any desensitization.

These data show that the neurotransmitter acetylcholine

can modulate frog adrenocortical function

and suggest that, in addition to more conventional

regulators, i.e. ACTH and angiotensin II, the

cholinergic endings of the splanchnic nerve might

participate in the regulation ofcorticosteroid secretion,

at least under so