Brain cyclooxygenase and prostanoid TP receptors are involved in centrally administered epibatidine-induced secretion of noradrenaline and adrenaline from the adrenal medulla in rats

Abstract

Plasma adrenaline mainly originates from adrenaline-containing cells in the adrenal medulla, whereas plasma noradrenaline reflects not only the release from sympathetic nerves but also the secretion from noradrenaline-containing cells in the adrenal medulla. The present study was undertaken to examine the mechanisms involved in centrally administered epibatidine (a potent agonist of nicotinic acethylcholine receptors)-induced elevation of plasma catecholamines with regard to the brain prostanoid. Intracerebroventricularly (i.c.v.) administered epibatidine (1, 5 and 10 nmol/animal) effectively elevated plasma noradrenaline and adrenaline. The epibatidine (5 nmol/animal, i.c.v.)-induced elevation of both catecholamines was attenuated by hexamethonium (an antagonist of nicotinic acethylcholine receptors) (0.9 and 1.8 µmol/animal, i.c.v.), indomethacin (an inhibitor of cyclooxygenase) (0.6 and 1.2 µmol/animal, i.c.v.) and (+)-S-145 (an antagonist of prostanoid TP receptors) (0.6 and 1.3 µmol/animal, i.c.v.), and abolished by acute bilateral adrenalectomy. On the other hand, intravenously administered epibatidine (5 nmol/animal) was largely ineffective on the plasma levels of catecholamines, and intravenous pretreatment with hexamethonium (1.8 µmol/animal) had no effect on the epibatidine (5 nmol/animal, i.c.v.)-induced elevation of both catecholamines. These results suggest that centrally administered epibatidine activates the brain nicotinic acethylcholine receptors, thereby evoking the secretion of noradrenaline and adrenaline from the adrenal medulla by brain cyclooxygenase- and prostanoid TP receptor-mediated mechanisms in rats.