Angiotensin neuromodulation of adrenergic and purinergic co‐transmission in the guinea‐pig vas deferens

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Abstract
1 The effects of angiotensin II (AII) and angiotensin III (AIII) on the isolated vas deferens of the guinea-pig were studied via three parameters: the overflow of adenosine 5′-triphosphate (ATP) and tritiated noradrenaline (NA), the mechanical response to field stimulation and the mechanical response to exogenous NA and α,β-methylene ATP (α,β-mATP). 2 At 2Hz, All enhanced the overflow of ATP and NA, whereas at 20 Hz, All enhanced the overflow of NA but was without significant effect on ATP overflow. AIII, at 2 Hz, inhibited the overflow of ATP, but enhanced NA overflow, whereas at 20 Hz ATP overflow was unaffected, but NA overflow was still enhanced. 3 At 2 Hz, AII enhanced both phases of the response to field stimulation and at 20 Hz the overall response. AIII at 2 Hz enhanced the adrenergic response, but was without effect on the purinergic response to field stimulation. At 20 Hz, AIII was without effect on the overall response. 4 AII enhanced responses to exogenous NA and α,β-mATP, whereas AIII was without effect. 5 These results provide evidence that both ATP and NA release are capable of being modulated by angiotensins. Furthermor, modulation of ATP release is frequency-dependent, whereas [3H]-NA release is not. These results raise questions about the mechanisms of storage and release of the sympathetic co-transmitters NA and ATP; they also show that angiotensin receptors in the guinea-pig vas deferens are not a homogeneous population.