INHIBITORY MECHANISMS OF DEXAMETHASONE ON CONTRACTIONS INDUCED BY DRUGS AND BY TRANSMURAL STIMULATIONS IN ISOLATED GUINEA PIG ILEUM

[摘要] References(10)Cited-By(3)Inhibitory effects of dexamethasone on contractile response of isolated ileum of guinea pig were isotonically investigated. Responses to picric acid and transmural stimulation at 50 Hz were employed for stimulations of cholinergic nerve and responses to potassium chloride and transmural stimulation at l Hz were taken as stimulation of smooth muscle, while response to acetylcholine was considered as stimulation of receptor sites. Dexamethasone significantly attenuated the contractile responses to cholinergic nerve stimulation in concentrations relatively lower than were required to depress the responses to muscle stimulations. The specific action of dexamethasone on receptor sites was not, however, responsible for this result as the dose-response curve of acetylcholine-induced contractions was shifted by dexamethasone to downward but not to the right side. Since the effect of dexamethasone was not modified in the reserpinized tissues and was not affected by treatment with tolazoline or propranolol, participation of adrenergic mechanisms in the effect of dexamethasone was ruled out. In addition, the effects of dexamethasone on both responses to nerve and muscle stimulations were reduced in a high calcium solution and potentiated in a low calcium solution. These results suggest that dexamethasone effects cholinergic nerve endings rather than acting on smooth muscle cells, and that interference with the movement of calcium ions is responsible for the inhibitory effect of dexamethasone.

[学科分类] 药理学