[Cardiovascular effects of MY-5116 and MY-1250]

The effects of MY-5116, isoamyl 5,6-dihydro-7,8-dimethyl-4,5-dioxo-4H-pyrano [3,2-c]quinoline-2-carboxylate, an anti-allergic drug, and MY-1250, an active metabolite of MY-5116, on the cardiovascular system were studied in dogs, rats and guinea pigs. Orally administered MY-5116 (300 mg/kg) had no effect on the cardiovascular system in anesthetized dogs and conscious rats. In anesthetized dogs, MY-1250 and disodium cromoglycate (DSCG) caused hypotension, bradycardia and reduction of respiration rate from the doses of 3 and 10 micrograms/kg, i.v., respectively. Both drugs showed a tachyphylaxic phenomena which was crossed with each other. MY-1250-induced cardiovascular effects were abolished by bilateral vagotomy. MY-1250 (3-30 micrograms/kg, i.v.) caused a decrease of carotid blood flow, a transient decrease followed by a slight increase of renal blood flow, and a transient increase followed by a slight decrease of femoral blood flow in anesthetized dogs. MY-1250 had no effect on sympathetic ganglion, but increased the contractile force of isolated left atria from guinea pigs at 10(-5) g/ml and increased its rate at 10(-4) g/ml. These positive inotropic and chronotropic effects were not influenced by reserpinization. MY-1250 had no effect on the norepinephrine-induced dose-response curve in isolated rat aorta.