Effects of neuropeptide Y (NPY) on mechanical activity and neurotransmission in the heart, vas deferens and urinary bladder of the guinea‐pig

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Abstract
The effects of preincubation for 10 min with synthetic porcine neuropeptide Y (NPY) on muscle tone and autonomic transmission in the guinea‐pig right atrium, vas deferens, urinary bladder, portal vein and trachea were analysed in vitro. NPY induced a metoprolol‐resistant, long‐lasting, positive inotropic and cronotropic effect per se in the spontaneously beating right atrium. Furthermore, NPY caused a reversible inhibition of both the metoprolol and atropine‐sensitive auricle responses to field stimulation (2 Hz or 4 Hz for 2 s) without affecting the response to exogenous noradrenaline (NA) or acetylcholine (ACh).NPY did not induce any contraction of the vas deferens, but inhibited both the rapid twitch response and the sustained tonic contraction induced by field stimulation. The NPY‐induced inhibition of the tonic contraction was more long‐lasting than that of the twitch response. The tonic contraction was blocked by phentolamine and the twitch response by α‐, β‐methylene ATP tachyphylaxis. NPY did not inhibit the contractile effects of NA, ATP or α‐, β‐methylene ATP. NPY also induced a reversible reduction of the non‐cholinergic, non‐adrenergic contractile response to field stimulation of the urinary bladder. In the portal vein, NPY (up to 5×10–7M) did not inhibit the spontaneous motility or the phentolamine‐sensitive contractile responses to field stimulation and NA. The atropine‐sensitive contraction of the trachea or the non‐adrenergic, non‐cholinergic relaxation induced by field stimulation were not significantly influenced by NPY in doses up to 5×10–7M. In conclusion, the present data show that in the guinea‐pig, NPY exerts positive chronotropic and inotropic effects on the right atrium of the heart. Furthermore, NPY may have presynaptic effects on adrenergic, cholinergic and non‐adrenergic—noncholinergic neurotransmission.