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SPECIES DIFFERENCES IN POSTGANGLIONIC MOTOR TRANSMISSION TO THE RETRACTOR PENIS MUSCLE
Author(s) -
AMBACHE N.,
KILLICK S.W.
Publication year - 1978
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.1476-5381.1978.tb07770.x
Subject(s) - phentolamine , phenoxybenzamine , reserpine , endocrinology , medicine , tetrodotoxin , guanethidine , adrenergic , acetylcholine , neuromuscular transmission , chemistry , papaverine , muscle contraction , bretylium , propranolol , stimulation , receptor
1 Graded motor responses were elicited in isolated, desheathed, thin strips of dog, horse, pig and sheep retractor penis (RP) muscles by field stimulation with trains of 0.2 ms pulses at 10 hertz. These twitches were shown to be neurogenic in all four species, by their prompt extinction in tetrodotoxin. 2 α‐Adrenoceptor blocking drugs abolished the contractile response to noradrenaline and to tyramine in all four species. 3 Motor transmission was wholly adrenergic in the horse as in the dog RP because phentolamine rapidly abolished the electrically induced twitches in both these species; but in the pig and in the sheep RP a large proportion of the motor transmission was unaffected by phentolamine given in many times the concentration required to abolish matching noradrenaline‐induced contractions. 4 Because of the occurrence of periodic spasms in sheep preparations, further investigation of the phentolamine‐resistant transmission was confined to the pig RP. Its responses were shown to be entirely postganglionic in origin because they were unaffected by pentolinium. 5 In the pig RP a considerable proportion of the phentolamine‐resistant motor transmission persisted after combined blockade of α‐ and β‐adrenoceptors by phenoxybenzamine plus propranolol and was more resistant to guanethidine and bretylium than the motor transmission to the dog RP; it was not extinguished after reserpine treatment. 6 The pig RP is contracted by histamine but is rather insensitive to acetylcholine, 5‐HYDROXYTRYPTAMINE and adenosines‐triphosphate. The motor transmission remained unaffected after responses to these substances were blocked by the following antagonists, given alone or in combination: mepyramine, burimamide, atropine, (+)‐tubocurarine, methysergide and 2–2′‐pyridylisatogen tosylate.