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At least 127 records · Page 7Linked to original sources
PubMed1976

Effect of bombesin, a natural tetradecapeptide, on myoelectrical and mechanical activity of isolated, ex vivo perfused, canine stomach.

Electrical and mechanical activity were recorded from the canine stomach, isolated and ex vivo perfused with homologous blood. The action of Bombesin, a natural tetradecapeptide, was compared with the action of pentagastrin, methacholine and electrical stimulation on the electrical and mechanical activity of this isolated preparation. All drugs used and vagal stimulation resulted in premature control potentials, uncoupling of the normal phase locked pattern of electrical control activity, appearance of response activity and appearance of mechanical reaction. These responses were blocked or decreased by atropine, tetrodotoxin and hexamethonium. It appears that the neural release of acetylcholine is implicated in the mechanism of action of Bombesin gastrointestinal motility.

Action Potentials↗
PubMed1987

Neural control of contraction in isolated submucosal gland from feline trachea.

To determine the autonomic innervation to myoepithelial cells of submucosal gland, we applied electrical field stimulation (FS) to the intrinsic nerves in isolated submucosal glands from feline tracheae. FS induced contraction that was voltage or frequency dependent and abolished by pretreatment with tetrodotoxin. DMPP (1,1-dimethyl-4-phenylpiperazinium iodide) did not produce any significant contraction, and pretreatment with hexamethonium did not alter the response to FS. Atropine inhibited the contractile response to FS and neostigmine augmented the response to FS. Serotonin also augmented the response to FS, whereas the response to methacholine remained unchanged in the presence of serotonin. Phentolamine reduced the response to FS by 15% of control, whereas propranolol induced no significant changes in the response to FS. No significant inhibitory responses were observed by FS. Our findings indicate that the contraction of tracheal submucosal glands is mediated mainly by cholinergic nerves via muscarinic receptors and in small part by adrenergic nerves via alpha-receptors, and serotonin potentiates the contractile response to FS at the postganglionic nerve.

Adrenergic Fibers↗
PubMed1985

Muscarinic receptors on bovine chromaffin cells mediate a rise in cytosolic calcium that is independent of extracellular calcium.

Although the mechanism by which nicotinic receptors on adrenal chromaffin cells regulate catecholamine secretion is reasonably well understood, that of the muscarinic receptors remains obscure. The effects of both acetylcholine and specific muscarinic agonists on cytosolic free calcium in isolated bovine adrenal chromaffin cells have been measured using the fluorescent probe Quin-2. Acetylcholine (0.1 mM) evokes a large increase in cytosolic free calcium from resting levels near 100 nM into the microM range, most of which is blocked by hexamethonium (0.5 mM) or removal of extracellular calcium. A small component of the acetylcholine-evoked rise in cytosolic free calcium (approximately 50-100 nM) is independent of extracellular calcium and is unaffected by 0.5 mM hexamethonium, but is totally blocked by 0.5 microM atropine. The muscarinic nature of this component is further confirmed by the fact that the muscarinic agonists, muscarine (0.1 mM) and methacholine (0.3 mM), stimulate a 50-100 nM rise in chromaffin cell cytosolic calcium which is blocked by 0.5 microM atropine and is largely independent of extracellular calcium. These results suggest that muscarinic receptors regulate cytosolic calcium in chromaffin cells by a new mechanism different from that of nicotinic receptors, a mechanism utilizing an intracellular calcium source. The small size of the muscarinic-induced rise in cytosolic calcium in the bovine chromaffin cell would explain why no secretion is evoked by muscarinic agonists in this species.

Acetylcholine↗
PubMed1975

Effect of metoclopramide on myoelectrical and mechanical activity of the isolated canine stomach perfused extracorporeally.

Totally isolated whole canine stomachs perfused, ex vivo, with homologous blood of living supporting dogs were used for recording of myoelectrical mechanical activities. Drugs were administered directly into the arterial system of the isolated stomachs either as flash injections or as constant infusions. Flash injection of metoclopramide (Maxeran) led to the response activity (spiking) and associated mechanical response. Electrical control activity was also affected by Maxeran: the changes consisted of premature control activity and uncoupling. Similar reactions were observed after flash injections of methacholine, pentagastrin or electrical stimulation of the Latarjet nerve. These reactions were dose-dependent. Tetrodotoxin, atropine, hexamethonium and glucagon, when given as a constant infusion, did inhibit the action of Maxeran on myoelectrical and mechanical activities of the isolated stomach. Inhibition of the responses to Maxeran by atropine and tetrodotoxin implicates acetylcholine in the mediation of these responses. The ability of hexamethonium to diminish the response to Maxeran suggests that a locus of action may be at both pre- and post-ganglionic sites of the intramural plexus. Exact receptors of this action are not demonstrated by this study.

Animals↗
PubMed1976

Mechanism of action of pentagastrin on the lower esophageal sphincter.

The effects of pentagastrin on lower esophageal sphincter (LES) pressure has been studied in trained, unanesthetized dogs. LES pressure was monitored by an infusion manometric technique. Increasing doses of pentagastrin up to 3 mug/kg given as an i.v. bolus resulted in increasing rises in LES pressure; larger doses resulted in a lesser effect of shorter duration. Increasing i.v. boluses of methacholine produced greater increases in LES pressure up to a maximum of 5 mug/kg; higher doses had similar effects. Atropine (50-100 mug/kg) slightly diminished the response of the LES to 2 or 6 mug/kg of pentagastrin. In large doses (500-2,000 mug/kg), atropine did not diminish the response to pentagastrin and prolonged the response of 6 mug/kg pentagastrin. Hexamethonium (2 mg/kg i.v.) depressed the peak response to 3 mug/kg pentagastrin slightly but the response to 6 mug/kg was increased and prolonged. Propranolol (2 mg/kg i.v.) significantly prolonged the effect of 6 mug/kg pentagastrin on the LES. We conclude that the stimulatory effect of pentagastrin is mainly due to a direct action on the LES. A lesser stimulatory effect is due to an action on preganglionic cholinergic neurons. Large doses of pentagastrin have both stimulatory and inhibitory effects. The inhibitory effect is mediated at least in part via preganglionic neurons acting through adrenergic receptors. Ganglionic transmission of the effect may be through muscarinic as well as nicotinic receptors.

Acetylcholine↗
PubMed1984

Mechanisms of substance P-induced contraction of rabbit airway smooth muscle.

The contractile effects of substance P (SP) were studied in isolated rabbit tracheal smooth muscle (TSM) segments in vitro. Noncumulative administration of SP produced dose-dependent increases in TSM tension. The mean (+/- SE) peak isometric tension (Tmax) with SP was 35.7 (+/- 6.2%) of the corresponding Tmax response to methacholine. The dose of agonist producing 50% of Tmax (ED50) was significantly lower for SP, averaging 1.8 (+/- 0.4) X 10(-7) M, vs. 1.7 (+/- 0.32) X 10(-6) M for methacholine. Blockade of both parasympathetic ganglia with hexamethonium (10(-4) M) and neural transmission with tetrodotoxin (1 microgram/ml) had no effect on the TSM response to SP. On the other hand, TSM contraction to an ED50 dose of SP was 1) augmented by a mean (+/- SE) of 470 (+/- 110%) following pretreatment with the cholinesterase inhibitor, neostigmine (10(-6) M);2) inhibited by a mean (+/- SE) of 35 (+/- 15%) with the cholinergic antagonist, atropine (10(-4) M); and 3) also inhibited by a mean (+/- SE) of 45 (+/- 11%) following inhibition of acetylcholine synthesis with hemicholinium-3 (10(-4) M). Antagonists to 5-hydroxytryptamine, alpha 1-adrenergic, and histamine receptor binding had no effect on TSM contraction with SP. In contrast, the SP antagonist, D-Pro2,D-Trp7,9-SP, markedly inhibited TSM contraction to SP. Our findings indicate that rabbit TSM is sensitive to SP and its contraction is in part mediated by a peripheral cholinergic action, likely involving the accelerated release of acetylcholine at the airway neuromuscular junction.

Animals↗
PubMed1981

Influence of cholinomimetics and cholinolytics on vestibular compensation.

The influence of cholinomimetics and cholinolytics on vestibular compensation was investigated in Rana temporaria. In compensated animals cholinomimetics induced a complete decompensation with reappearance of all symptoms characteristic of the precompensated state. Cholinolytic exerted antagonistic effects. They induced postural and locomotor symptoms which were a mirror-image of those observed in the precompensated state. The findings support the assumption that the compensatory reorganization of the vestibular system involves the modification of cholinergic brain stem synapses.

Animals↗