Field stimulation-induced responses of circular smooth muscle from guinea-pig stomach

Characterisation of the receptor mechanisms involved
  • Brenda Costall
  • Robert J. Naylor
  • Connie C. W. Tan
Article

Summary

Field stimulation of circular smooth muscle of guinea-pig stomach from the regions of the cardia and fundus caused contraction responses at low stimulation frequencies (0.25–1 Hz) with relaxation at higher frequencies (1–10 Hz), whilst tissues of the body and antrum responded with contraction throughout the frequency range. Atropine (10−9–10−8 M) antagonised the contraction responses of all tissues, with relaxation developing at higher concentrations (except for antral tissue). In contrast, metoclopramide (10−8–10−6 M) caused modest (cardia, fundus) or marked (body, antrum) enhancement of contractions to field stimulation, whilst domperidone (10−8–10−7 M), haloperidol (10−8–10−6 M), prazosin, propranolol and methysergide (10−8–10−6 M) failed to modify the contraction responses. However, whilst yohimbine and guanethidine failed to modify the contractions of the cardia, fundus and body tissues, those of the antral preparations were antagonised by nanomolar concentrations of yohimbine and by guanethidine (10−6–5×10−5 M). To optimise the relaxation responses for study, atropine was included in the physiological solution. Relaxation to field stimulation of preparations from the body and cardia, but not the fundus, was antagonised by reserpine pretreatment (5 mg/kg i.p., 24h), addition of guanethidine (10−5–10−4 M), phentolamine, prazosin or propranolol (10−7–10−6 M) (the effects of prazosin and propranolol being additive). Higher concentrations of haloperidol and domperidone antagonised the relaxation responses of the body preparations only. Metoclopramide, yohimbine and methysergide (10−8–10−6 M) were ineffective. Thus, it is concluded that the contractile effects of the 4 stomach areas to field stimulation reflects a major cholinergic involvement, with an additional α2-adrenoceptor contractile component in antral tissue. Relaxation responses of cardia and body tissue involve α2- and β-adrenoceptors plus a further, unidentified, non-adrenergic component; the latter represents the total relaxation response of the fundic preparation.

Key words

Guinea-Pig Stomach musculature Field stimulation Cholinergic contraction Sympathetic relaxation 

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Copyright information

© Springer-Verlag 1983

Authors and Affiliations

  • Brenda Costall
    • 1
  • Robert J. Naylor
    • 1
  • Connie C. W. Tan
    • 1
  1. 1.Postgraduate School of Studies in PharmacologyUniversity of BradfordBradfordUK

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