The effects of dopaminergic and adrenergic drugs on twitch response of guinea-pig common bile duct.
1. Effects of various doses of bromocriptine and apomorphine, dopamine receptor agonists, on electrically evoked contractile responses of guinea pig common bile duct (CBD) were investigated in this study. 2. Bromocriptine and apomorphine produced a concentration-dependent reduction of the twitch heights. IC50 values for bromocriptine and apomorphine were 2.75 +/- 0.715 x 10(-6) M, and 1.69 +/- 0.11 x 10(-5) M, respectively. 3. Pretreatment with sulpiride, 0.1 and 1.0 microM, prevented bromocriptine- and apomorphine-induced inhibition. pA2 values of sulpiride against bromocriptine and apomorphine were 8.26 and 6.29, respectively. 4. Clonidine, 0.1-100 microM, produced 49.3 +/- 2.5% inhibition of twitch responses. Its effect was partially antagonized by 1 microM of yohimbine. 5. It would appear that both dopamine D2- and alpha 2-adrenergic presynaptic receptors are present on the guinea-pig CBD cholinergic nerve.
Samini
M
M
Department of Pharmacology, School of Medicine, Tehran University of Medical Sciences, Iran.
Dehpour
A R
AR
Yousefnejad
S
S
D018663:Adrenergic Agents / Q000494:pharmacology*; D000316:Adrenergic alpha-Agonists / Q000494:pharmacology; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology; D000818:Animals; D001058:Apomorphine / Q000494:pharmacology; D001971:Bromocriptine / Q000494:pharmacology; D003135:Common Bile Duct / Q000187:drug effects / Q000502:physiology*; D015259:Dopamine Agents / Q000494:pharmacology*; D018491:Dopamine Agonists / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D004558:Electric Stimulation; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*
D018663:Adrenergic Agents; D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D015259:Dopamine Agents; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D018727:Muscarinic Antagonists; D001971:Bromocriptine; D001058:Apomorphine