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The inhibitory effect of somatostatin peptides on the rat anococcygeus muscle in vitro
Author(s) -
Priestley T.,
Woodruff G.N.
Publication year - 1988
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1988.tb11502.x
Subject(s) - stimulation , somatostatin , inhibitory postsynaptic potential , medicine , endocrinology , tonic (physiology) , chemistry , guanethidine , receptor , calcium , biology
1 Electrically evoked contractions of the rat anococcygeus muscle were inhibited in a concentration‐dependent manner by somatostatin‐14 (SS14), −28 (SS28) and two synthetic hexapeptide analogues: L‐363,301 and L‐363,586 , with pIC 50 values of 7.41, 7.38, 7.07 and 8.34, respectively. 2 The inhibitory effects of SS14 were dependent on stimulation frequency and external calcium ion concentration. Calcium behaved as a non‐competitive antagonist of SS14, it reduced the maximal inhibitory effect of the peptide and at a concentration of 5.08 m m it significantly affected the pIC 50 value. 3 SS14 (3 times 10 −7 m ) did not affect the tonic actions of bath‐applied noradrenaline in the absence of field stimulation. 4 The effects of SS14 persisted in naloxone (10 −5 m ) and were, therefore, not due to an action at opiate receptors. Furthermore, experiments involving the lyophilisation of bath contents, showed no evidence to support an indirect mechanism involving the release of an endogenous inhibitory substance. 5 High concentrations (10 −5 m ) of SS14 or L‐363,301 inhibited the relaxation response evoked by electrical stimulation of guanethidine (3 times 10 −4 m )‐treated preparations. 6 These results are consistent with similar actions of SS14 on other smooth muscle preparations and are presumed to reflect a presynaptic inhibition of transmitter release by a direct action on somatostatin receptors. The antagonistic effect of calcium on this response is discussed with reference to a possible role in receptor desensitization.