Hypotensive effect of dl-2-(3, 4-methylenedioxyphenyl)-2-hydroxyacetamidine hydrochloride (dl-mandelamidine) and its optical isomers (l-mandelamidine, d-mandelamidine) was examined. All the compounds used in the present experiment caused long-lasting hypotensive effect on the systolic blood pressure in both unanesthetized spontaneously hypertensive rats and unanesthetized normotensive Wistar rats). Moreover, these three compounds produced a temporary hypotensive effect followed by long lasting ones on the carotid blood pressure in normotensive Wistar rats anesthetized with urethane. In spontaneously hypertensive rats, the long-lasting hypotensive effect of l-mandelamidine) (50-100mg/kg, oral) was rather potent than those of d- and dl-mandelamidine (50-100mg/kg, oral). On the other hand, the hypotensive effect of l-mandelamidine (100-200mg/kg, oral or 10-30mg/kg, intravenous) was the same degree as those of d-and dl-mandelamidine (100-200mg/kg, oral or 10-30mg/kg, intravenous) in unanesthetized or anesthetized normotensive Wistar rats. The sympathetic nerve-blocking action of three compounds were studied by the inhibitory responses of isolated rabbit jejunum to the mesenteric perivascu1ar nerve stimulation and the contraction of the anesthetized cat nictitating membrane to the preganglionic stimulation of cervical sympathetic nerve. d-Mandelamidine (1×10
-4g/ml or 5 mg/kg, intravenous) showed the most potent blocking action of both responses. The contractions of the anesthetized cat nictitating membrane to norepinephrine and epinephrine was potentiated by d-and dl-mandelamidine (5mg/kg, intravenous), but inhibited by l-mandelamidine (5mg/kg, intravenous). In the guinea-pig atria, the compounds (10
-7-10
-3g/ml) used herein showed negative inotropic and chronotropic actions, and these actions of l-mandelamidine were the most potent. Thus, it is likely that pharmacological action of the optical isomers of dl-mandelamidine is different from that of dl-mandelamidine.
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