Modulation of pyloric motor activity via adrenergic receptors
Allescher, H.D.; Ahmad, S.; Kostolanska, F.; Kwan, C.Y.; Daniel, E.E.
Journal of Pharmacology and Experimental Therapeutics 249(2): 652-659
1989
ISSN/ISBN: 0022-3565 PMID: 2724146 Document Number: 340938
The influences of adrenergic nerves on pyloric motor function and the locus and types of receptors involved were examined. Using glyoxylic acid fluorescence a dense adrenergic innervation of the inner pyloric muscle ring was demonstrated. Pyloric motor activity was monitored with close i.a. injections of a selective alpha-1 adrenoceptor agonist, phenylephrine, or a selective alpha-2 adrenoceptor agonist, B-HT-920, were given. Neither agonist affected basal pyloric motor activity, but both inhibited pyloric activity when it was stimulated by duodenal field stimulation or by intraduodenal acid infusion. The actions of each of the inhibitory agonists, phenylephrine or B-HT-920, were blocked selectively by prazosin or rauwolscine, respectively. Injection of isoproterenol usually had no effect or excited basal pyloric activity. This excitation could be antagonized selectively by propranolol or by atropine. Injection of isoproterenol after neural blockade by tetrodotoxin inhibited pyloric motor activity. Receptor binding studies carried out with subcellular nerve or muscle enriched membrane fractions of canine pyloric muscle with [3H]prazosin, [3H]rauwolscine and [125I]cyanopindolol revealed a dual location of alpha-1, alpha-2 and beta receptors on both nerve membranes and smooth muscle membranes. These results suggest that adrenergic effects on the pyloric muscle can be exerted by pre- and postsynaptic beta receptors which, respectively, excite by releasing acetylcholine and inhibit by acting on receptors on the pyloric muscle. Also inhibitory alpha-1 and alpha-2 receptors are preesnt on cholinergic nerves. The functions of postsynaptic alpha-1 and alpha-2 adrenoreceptor binding sites on smooth muscle are so far unknown.