Actions of α, β‐methylene ATP and 6‐hydroxydopamine on sympathetic neurotransmission in the vas deferens of the guinea‐pig, rat and mouse: support for co‐transmission

Abstract

1 α-Adrenoceptor antagonists (prazosin or phentolamine) reduced the contractile response to field stimulation of the isolated vasa deferentia of guinea-pig, rat and mouse. α, β-Methylene ATP (α, β-MeATP) reduced that portion of the contraction which was resistant to α-adrenoceptor blockade. 2 α, β-MeATP (1–800 μM) did not affect action potential conduction in the guinea-pig vas deferens nerves, and (up to 10 μM) did not reduce the stimulation-evoked overflow of [³H]-noradrenaline from this tissue. 3 Spontaneous excitatory junction potentials (s.e. j.ps) in the majority of cells of guinea-pig, rat, and mouse vasa were abolished by α, β-MeATP (0.1–10 μM). In a small number of cells s.e.j.ps were resistant to the actions of α, β-MeATP (10 μM). 4 Excitatory junction potentials (e.j.ps) in the majority of cells in vasa of all species studied were abolished by α, β-MeATP (1–10 μM). E.j.ps elicited in some ‘resistant’ cells demonstrated marked facilitation characteristics. 5 It is concluded that α, β-MeATP inhibits s.e.j.ps and e.j.ps by a postjunctional action. 6 In all species pretreatment of animals with 6-hydroxydopamine produced a marked reduction in noradrenaline (NA) content (as determined by fluorescence histochemistry) and abolished e.j.ps, findings which suggest that e.j.ps originated from sympathetic nerves. 7 The results support the hypothesis that NA and ATP are co-transmitters in the sympathetic nerves of rodent vasa.