Characterization of alpha1-adrenoceptor subtypes mediating noradrenaline-induced contraction of rat epididymal vas deferens in calcium-free medium.
The alpha1-adrenoceptor subtype mediating noradrenaline (NA)-induced contractions of rat epididymal vas deferens in Ca2+-free/EGTA (1 mM) medium was studied using competitive antagonists. The effects of chloroethylclonidine (CEC) was investigated in Ca2+-free and normal Krebs' medium and RT-PCR was used to identify alpha1-adrenoceptor specific mRNA in epididymal vas deferens. In Ca2+-free medium, NA evoked sustained contractions but was less potent (pD2, 5.9) than in normal Krebs' medium (pD2, 7.3). The contractions in Ca2+-free medium were inhibited by prazosin (pA2, 9.3), 5-methylurapidil (pA2, 8.4), spiperone (pA2, 7.6) and BMY 7378 (pK(B), 6.8) consistent with activation of alpha1A-subtype. Repeated pretreatment with CEC (100 microM) reduced the potency of NA and maximum contractions in normal and Ca2+-free media. CEC-sensitivity in normal Krebs' medium was enhanced by prior treatment with phenoxybenzamine. mRNA for alpha1a- and alpha1d- but not alpha1b-adrenoceptors were detected in epididymal vas deferens. These results suggest that NA contracts the tissue in Ca2+-free medium by the stimulation of alpha1A-adrenoceptors. Two factors affecting CEC-sensitivity of NA-induced contractions in this tissue are discussed.
Amobi
N I
NI
Physiology Division, King's College London, Great Britain, UK.
Sugden
D
D
Smith
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IC
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000494:pharmacology; D002952:Citric Acid Cycle; D003000:Clonidine / Q000031:analogs & derivatives / Q000494:pharmacology; D003470:Culture Media; D004822:Epididymis; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009638:Norepinephrine / Q000494:pharmacology*; D010643:Phenoxybenzamine / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014649:Vas Deferens / Q000502:physiology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D003470:Culture Media; D010643:Phenoxybenzamine; C051731:chlorethylclonidine; D003000:Clonidine; D002118:Calcium; D009638:Norepinephrine