THE EFFECTS OF VASOACTIVE INTESTINAL POLYPEPTIDE AND OF ADENOSINE 5′‐TRIPHOSPHATE ON THE ISOLATED ANOCOCCYGEUS MUSCLE OF THE MOUSE

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Abstract
1 Vasoactive intestinal polypeptide (VIP, 0.01–5 μm) produced dose-related relaxations of the mouse anococcygeus muscle. 2 Following incubation with indomethacin (2.8 μm 1 h) adenosine 5′-triphosphate (ATP, 0.5–10 mm) produced dose-related relaxations of the mouse anococcygeus. 3 Haemolysed blood reduced inhibitory responses of the mouse anococcygeus to field stimulation but had no effect on relaxations to VIP or ATP. 4 Apamin (0.5 μm) had no effect on the relaxation of mouse anococcygeus to field stimulation, VIP, or ATP. 5 2-2′-Pyridylisatogen tosylate (PIT, 50 μm) itself reduced muscle tone but it did not abolish inhibitory responses to field stimulation, VIP, or ATP. 6 During prolonged inhibitory nerve stimulation the relaxation of the mouse anococcygeus in response to VIP was reduced greatly while that to ATP was unaffected. 7 Bundles of VIP-immunoreactive sites were detected in sections of the mouse anococcygeus treated by the peroxidase-antiperoxidase (PAP) immunocytochemical technique. 8 The results suggest that the mechanisms underlying non-adrenergic, non-cholinergic inhibitory transmission in the mouse anococcygeus are similar to those in the bovine retractor penis and unlike those in the guinea-pig taenia caeci. 9 The possibility that VIP or ATP might be involved in inhibitory neurotransmission in the mouse anococcygeus is discussed.

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