EFFECTS OF AMINOGUANIDINE AND L-NAME ON HISTAMINE-INDUCED BLOOD-PRESSURE DROP IN THE RAT

Mean arterial blood pressure changes in response to i.v. administratio n of histamine were monitored in the anaesthetized rat in the absence or presence of the diamine oxidase (DAO) inhibitor aminoguanidine (AMG , 10 mg kg(-1)). AMG prolonged the duration of the transient drop in b lood pressure induced by a bolus injection of histamine (0.05 mg kg(-1 )) by 34%. In animals pretreated with AMG, no potentiation of the decr ease in pressure in response to a 10 min infusion of histamine was obs erved. However, when infusion was stopped, the time needed for pressur e recovery was twice as long in animals treated with AMG as in control s. Blood samples were taken prior to infusion and during the recovery phase and the quantities of histamine were determined by liquid chroma tography. The prolonged recovery phase observed in animals pretreated with AMG was associated with five times higher levels of histamine. Th e curation of histamine-induced hypotension (0.01 mg kg(-1)) was 50% s horter in the presence of the nitric oxide synthase inhibitor I-NAME ( 10 mg kg(-1)). We suggest that DAO, through elimination of histamine f rom the bloodstream, is important for the recovery from histamine-indu ced hypotension, and that the duration of histamine-induced pressure d rop is influenced by formation of nitric oxide.