SELECTIVE STIMULATION OF VASCULAR POSTJUNCTIONAL α1‐ADRENORECEPTORS BY (‐)‐AMIDEPHRINE IN RATS AND CATS

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Abstract
The vasopressor and chronotropic responses of (-)-amidephrine and the receptor types involved were studied in pithed rats of different strains and in pithed cats. The increase in diastolic pressure of pithed rats after i.v. administration of (-)-amidephrine was not influenced by pretreatment with propranolol (1 mg/kg, i.v.), reserpine (2 .times. 5 mg/kg in 48 h i.p.) or yohimbine (1 mg/kg, i.v.) but was strongly antagonized by prazosin (0.1 mg/kg, i.v.). In pithed cats, the pressor responses were antagonized by prazosin (1 mg/kg, i.v.) but less so by yohimbine (1 mg/kg, i.v.). (-)-Amidephrine elicited minor positive chronotropic responses in pithed rats and pithed cats. This tachycardia was not influenced by propranol (1 mg/kg, i.v) but was abolished by prazosin (0.1-1.0 mg/kg). Apparently, (-)-amidephrine acts as a selective agonist at vascular postjunctional .alpha.1-adrenoreceptors in pithed rats and pithed cats. The positive chronotropic effects are attributable to stimulation of .alpha.1-adrenoreceptors in the heart.