The effect of some alpha 2-adrenoceptor agonists and antagonists on gastrointestinal transit in mice: influence of morphine, castor oil and glucose.
1. The effects of graded doses of the alpha 2-adrenoceptor agonists clonidine, tizanidine and BHT-920, and the alpha 2-adrenoceptor antagonists yohimbine and idazoxan, on gastrointestinal transit were investigated in mice using the charcoal meal test. 2. The agonists produced significant and dose-dependent decreases in gastrointestinal transit, and the antagonists produced the opposite effect. In affecting the gastrointestinal transit, clonidine (1 mg/kg) was as effective as tizanidine (12 mg/kg) and BHT-920 (40 mg/kg), while yohimbine (2 mg/kg) was as effective as idazoxan (1 mg/kg). 3. Morphine (2, 4 and 8 mg/kg) significantly inhibited gastrointestinal transit. This effect was significantly reversed by the co-administration of yohimbine (2 mg/kg) and idazoxan (1 mg/kg). 4. The acute administration of glucose (5.04 g/kg, i.p.) potentiated the inhibition of gastrointestinal transit produced by clonidine (1 mg/kg) and BHT-920 (40 mg/kg). Glucose treatment, however, had no significant effect on the increase in gastrointestinal transit induced by yohimbine (2 mg/kg) or idazoxan (1 mg/kg). 5. Castor oil (0.25 mL/mouse, orally) induced diarrhoea in saline-treated animals within about 45 min. Clonidine (1 mg/kg), tizanidine (12 mg/kg) and BHT-920 (40 mg/kg) delayed the occurrence of diarrhoea to 2.1, 1.2 and 1.4 h, respectively.
Ali
B H
BH
Department of Pharmacology, Faculty of Medicine, Al-Arab Medical University, Benghazi, Libya.
Bashir
A A
AA
D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000317:Adrenergic alpha-Antagonists / Q000494:pharmacology*; D000818:Animals; D002368:Castor Oil / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004347:Drug Interactions; D005772:Gastrointestinal Transit / Q000187:drug effects*; D005947:Glucose / Q000494:pharmacology*; D008297:Male; D051379:Mice; D009020:Morphine / Q000494:pharmacology*
D000316:Adrenergic alpha-Agonists; D000317:Adrenergic alpha-Antagonists; D009020:Morphine; D002368:Castor Oil; D005947:Glucose