The effect of
vasopressin and
oxytocin on the contractile activity of preparations isolated from the feline gastric corpus wall was investigated.
Vasopressin (1.5 x 10(-9)-2.1 x 10(-7) M), but not
oxytocin, evoked concentration-dependent tonic contractions only of longitudinal muscle strips. At the same time,
vasopressin (1.5 x 10(-9)-2.1 x 10(-7) M) potentiated the magnitude of amplitudes, but not the frequency, of spontaneous contractions. Both the
vasopressin V1 receptor antagonist d(CH2)5-(Me)2-Tyr-AVP and the predominantly
vasopressin V2 receptor antagonist d(CH2)5, D-Ile2, Ile4-AVP, the non-selective
muscarinic receptor antagonist,
atropine, the predominantly selective
muscarinic M1 receptor antagonist,
pirenzepine, the predominantly selective
muscarinic M2 antagonist,
methoctramine, the predominantly selective
muscarinic M3 receptor antagonist, para-fluoro-hexahydro-siladifenidol, and the
calcium channel blocker,
nifedipine, but not the
ganglion blocking agent,
mecamylamine, depressed or blocked the tonic contractions induced by
vasopressin. Among the antagonists, only
atropine and
nifedipine inhibited the spontaneous contractions. On the other hand, the
anticholinesterase,
physostigmine, potentiated both the
vasopressin-induced tonic and spontaneous contractions. With regard to the receptors, the
vasopressin-induced tonic contractions are mediated at least in part through
vasopressin V1 and
V2 receptors, non-selective
muscarinic and selective
muscarinic M1, M2 and M3 receptors. The increase in amplitudes of spontaneous contractions is mediated only via-nonselective
muscarinic receptors.
Vasopressin receptors appear to be located mostly pre-synaptically, although the direct effect of
vasopressin on post-
synaptic receptors cannot be excluded. The pA2 values suggests rather V1a than
V1b vasopressin receptor subtype involvement in tonic contractions
vasopressin had produced. The tonic as well as spontaneous contractions are
calcium-dependent. In addition, these results point to the existence of non-selective
muscarinic receptors, which participate in the regulation of both tonic and spontaneous contractions, while
muscarinic M1, M2 and M3 receptors subserve only the tonic contractions.