Facilitating effect of harmaline on phenylephrine contraction in rabbit urethra

Harmaline, the drug first extracted from Peganum harmala L. seeds, has been well known since ancient times for its CNS stimulant activity. P. harmala L. seeds contain many alkaloids, but harmaline and harmine seem to be the most effective compounds for the hallucinogenic activity. Our experiments on aortic strips had shown that harmaline facilitates the contracting effect mediated by phenylephrine and adrenaline at doses devoid of direct action. The aim of this study was to ascertain if this effect was present in another tissue and, in this case, to investigate the underlying mechanism. Reported results show the facilitating effect of harmaline on phenylephrine evoked response on rabbit urethra and indicate that this effect has a different modulation on urethral and aortic strips.