THE A₁ AND NON A₁EFFECTS OF N⁶-(5-HYDROXY-2-PYRIDYL)-METHYL-ADENOSINE ON RAT VAS DEFERENS

N⁶-(5-hydroxy-2-pyridyl)-methyl-adenosine (HPMA) is a novel N⁶-substituted adenosine analogue recently obtained from Armillaria mellea (an edible fungus on which depends the growth of the famous Chinese traditional drug Gastrodia elata). It has been shown to have some characters of A₁ receptor agonists of purinergic nerve. In this study, we compared the effects of HPMA with that of N⁶-Cyclohexyladenosine(CHA), an A₁ selective agonist, on rat vas deferens in vitro, and found remarkable differences between them. In our study, HPMA dosedependently decreased the contraction responses to exogenous Phenylephrine(PE), Norepinephrine(NE) and Acetylcholine(ACh) on rat vas deferens, while CHA showed no effect on these responses. 8-Cyclopentyl-1,3-dipropylxanthine(DPCPX), an A₁ selective antagonist, did not show any influence on these effects of HPMA, indicating that the depression effect of HPMA may be through a nonA₁ mechanism. Using HPMA to decrease about 50% of the twitch responses evoked by fieldstimulation on rat vas deferens, the responsiveness to exogenous ACh seemed to be similar to that without HPMA pretreatment. These indicate that HPMA at this dosage (IC₅₀dosage) preferentially acted on pre-synapse (may be the A₁ receptor) to attenuate the release of neurotransmitters. At a high dosage(10^-5 mol·L^-1), HPMA abolished the neurogenic twitch responses evoked by electrical field-stimulation, while the responsiveness of rat vas deferens to exogenous ACh was decreased showing both pre-synapse and post-synapse depression.