A study of the actions of P1-purinoceptor agonists and antagonists in the mouse vas deferens in vitro

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Abstract
1 We have examined the effects of purinoceptor agonists and antagonists on the mechanical ‘twitch’ response, excitatory junction potential (e.j.p.) amplitude and [3H]-noradrenaline overflow in the mouse vas deferens. 2 The agonist profile for inhibition of the mechanical response was N6-([R]-2-phenylisopropyl)adenosine (l-PIA) ⋍ N6-cyclohexyladenosine (CHA) > 5′ N-ethylcarboxamidoadenosine (NECA) > 2-chloroadenosine (2ClA) ⋍ N6-([S]-2-phenylisopropyl)adenosine (d-PIA). 3 The P1-purinoceptor agonists inhibited the e.j.p. with an agonist profile of CHA > l-PIA NECA > 2ClA. 4 2ClA inhibited [3H]-noradrenaline overflow with an EC50 of 1.2 μm which was not significantly different from the values for inhibition of the e.j.p. and the mechanical response. 5 The inhibitory action of 2ClA on the mechanical response was antagonized by 5 μm 8-phenyltheophylline (8-PT). However, neither blockade of P1-purinoceptors by 8-PT nor increasing the rate of degradation of endogenous adenosine by addition of adenosine deaminase had any effect on the mechanical response per se. 8-PT (5 μm) also failed to alter the e.j.p. amplitude or [3H]-noradrenaline overflow. 6 These results indicate that there are P1-purinoceptors present on sympathetic nerve terminals of the mouse vas deferens which are more like A1- than A2-receptors, but may be better classified as being of the A3-subtype (Ribeiro & Sebastiao, 1986). These receptors are not normally involved in the feedback regulation of transmitter release in this tissue.