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Saito H, Kitagawa H. 
“Mechanisms of the reversal of blood pressure by ephedrine”. 
Jap.J.Pharmacol.. 1976;26(Suppl.):149P.
In rats anesthetized with urethane (1.75 g/kg s.c.), the reversal of B.P. by d-ephedrine (10 mg/kg i.v.) after the injection of l-isomer (10 mg/kg i.v.) was abolished by pretreatment with phenoxybenzamine (2.5 mg/kg i.v.), chlorpromazine (2.5 mg/kg i.v.), sulpiride 12.5 mg/kg i.v. and LSD-25 (200 mg/kg i.v.), respectively. The reversal by d-isomer did not disappear with vagotomy and cocaine pretreatment (10 mg/kg i.v.). The reversal was evident in spinal rats and rats given p-chlorophenylalanine (300 mg/kg i.p. for 3 days). The depressor effect of d-isomer was potentiated by tryptophan (1000 mg/kg p.o. before 4 hr). In rats given iproniazid (300 mg/kg i.p. before 8 hr) in addition to tryptophan, the decrease in B.P. was much greater than with tryptophan alone. In rats administered Li2CO3 (2 mEq/ kg p.o. twice daily x 5), the decrease in B.P. was increased 2fold whereas the level of 5-HT in blood obtained from rat carotid artery was increased with reversal of B.P.-by D-isomer.: Release of 5-HT from rat platelets occurred on incubation (37íC 20 min) with both d-and l-isomer (3 x 10 3 g/ml). These data indicate that the reversal of B.P. by d-isomer was mediated by 5-HT. These results provide additional data to the Author's previous- study (Japan. J. Pharmacol. 25, Suppl. 148, 1975). (1) As initial injection of l-isomer caused a pressor effect and masked a-action, therefore, the presser effect of d-isomer disappeared with the 2nd injection. (2) The depressor effect of endogenous 5-HT appeared. (3) Endogenous 5-HT was released from platelets by the d-isomer. (4) The depressor effect was partially due to dilation of the peripheral blood vessels by the direct and indirect action of the d-isomer.
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