Effect of intraventricular administration of adrenergic agonists and antagonists on plasma adrenaline and corticosteroid levels in conscious rats

Abstract In attempt to clarify the possible contribution of the central adrenergic system to control of adrenal secretion, we examined effects of intraventricular (i.v.c.) administration of adrenergic agonists or antagonists on levels of plasma adrenaline(Ad) and corticosteroid(CS) in conscious rats. Blood samples were obtained through a thin catheter kept in the jugular vein of conscious rats. Stress was given to the conscious rats by restraining them supinely on the plates forcibly for 30 min after i.v.c. administration of reagents. When saline(25μl) was given intraventricularly and then the rats were exposed to the stress, plasma Ad level was markedly increased in a linear manner. Noradrenaline(lng) i.v.c. administration followed by forced immobilization stress caused very small increase in plasma Ad, indicating i.v.c. administration of noradrenaline clearly suppressed increase in plasma Ad by the stress. The same finding was obtained with phenylephrine(lng), but was not observed with isoproterenol (1ng). By administering(i.v.c.) phentolamine(1lμg) prior to noradrenaline, the suppression of plasma Ad increase by the stress was markedly inhibited. When propranolol(1μg) was administered before noradrenaline, the suppression of increase in plasma Ad level was not changed in contrast with phentolamine. Plasma CS level was increased by stress, but it was not suppressed by i.v.c. administration of noradrenaline. In summary, we obtained a new finding in these experiments indicating that the central α-adrenergic mechanism should act to suppress the secretion of adrenal catecholamine.