title: Central alpha 2-adrenergic control of the pattern of small intestinal motility in rats.
abstract: The effects of central and peripheral administration of alpha 2-adrenoceptor agonists and antagonists on small intestinal motility were examined in conscious rats chronically fitted with electrodes implanted in the duodenojejunal wall and a cannula placed in a cerebral lateral ventricle. In fasted rats, intracerebroventricular or intraperitoneal administration of clonidine (5 micrograms) immediately disrupted the migrating myoelectric complex pattern with a total inhibition of spiking activity during the first hour, followed by a period of irregular spiking activity for 2 h. The inhibition was abolished by previous intramuscular administration of yohimbine (600 micrograms), and the period of irregular activity was suppressed by intracerebroventricular yohimbine (30 micrograms). Naphazoline, an alpha 2-agonist that poorly crosses the blood-brain barrier, only inhibited spiking activity when administered intraperitoneally (1 microgram) and induced only a period of irregular spiking activity when administered intracerebroventricularly at the same dose. In fed rats, intracerebroventricular administration of yohimbine or phentolamine (30 micrograms), and to a lesser extent prazosin, restores a migrating myoelectric complex pattern typical of the fasted state. Peripheral administration of these three antagonists at a dose 20 times higher was ineffective. Finally, both feeding and central administration of alpha 2-agonists disrupt the migrating myoelectric complex pattern. Such pharmacologic data suggest a possible role of central alpha 2-adrenoceptors in the regulation of intestinal motility in rats.
mesh_terms: D000818:Animals; D003000:Clonidine / Q000037:antagonists & inhibitors / Q000494:pharmacology; D004386:Duodenum / Q000187:drug effects / Q000502:physiology*; D004435:Eating; D004576:Electromyography; D005215:Fasting; D005769:Gastrointestinal Motility / Q000187:drug effects; D007583:Jejunum / Q000187:drug effects / Q000502:physiology*; D008297:Male; D009278:Naphazoline / Q000494:pharmacology; D010646:Phentolamine / Q000494:pharmacology; D011224:Prazosin / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D011942:Receptors, Adrenergic, alpha / Q000187:drug effects / Q000502:physiology*; D015016:Yohimbine / Q000494:pharmacology
chemical_list: D011942:Receptors, Adrenergic, alpha; D015016:Yohimbine; D009278:Naphazoline; D003000:Clonidine; D011224:Prazosin; D010646:Phentolamine