Intra-arterial injections of substance p in doses from 10 to 30 units potentiated the response of the nictitating membrane to submaximal stimulation of the preganglionic sympathetic nerve, while higher doses (30 to 100 units) usually depressed the response. The stimulating action of acetylcholine on the superior cervical ganglion (as judged by the response of the nictitating membrane) was also potentiated by substance P. The responses of the nictitating membrane to adrenaline, noradrenaline and tyramine were potentiated by substance P as well. It is concluded that the potentiating effect of substance P on the response of the nictitating membrane to submaximal stimulation of the preganglionic sympathetic nerve is probably due to sensitization of acetylcholine receptors in the postsynaptic neurone. The present experiments do not explain how substance P potentiated the response to sympathomimetic amines.

Acetylcholine↗

PubMed1959

The effect of substance P on the peristaltic reflex when acting on the outside of the isolated guinea pig ileum.

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Guinea Pigs↗

PubMed1958

The effect of cooling and of 5-hydroxytryptamine on the peristaltic reflex of the isolated guinea-pig ileum.

Cooling the guinea-pig ileum to 19 to 26 degrees abolished the emptying phase of the peristaltic reflex. The effects of cooling to 10 degrees were usually reversible, but cooling to 5 degrees for 3 to 8 hr. produced an irreversible decrease in or abolition of the emptying phase. 5-Hydroxytryptamine (5-HT) added in low concentrations to the fluid outside the intestine restored slight peristaltic activity after this activity had been abolished by cooling. If the peristalsis had been depressed but not abolished by cooling, 5-HT in the bath sometimes abolished it. 5-HT introduced into the lumen of the cooled gut regularly restored or increased peristaltic activity. This action was prevented by previous injection of 2-bromolysergic acid diethylamide into the lumen. It is suggested that, when introduced into the lumen, 5-HT may sensitize the sensory receptors in the mucosa of the cooled intestine. When applied outside, 5-HT may facilitate transmission at synapses involved in the peristaltic reflex arc, the excitability of which has been depressed by cooling.

Cold Temperature↗

PubMed1958

The effect of substance P on the peristaltic reflex of the isolated guinea-pig ileum.

The introduction of substance P into the lumen of the isolated guinea-pig ileum caused an increase in the number and amplitude of the peristaltic waves. In preparations in which the peristaltic reflex was abolished, by fatigue, by external or internal application of 5-hydroxytryptamine, or by lowering the temperature of the bath, the introduction of substance P into the lumen of the intestine restored peristalsis. This effect of substance P was absent in preparations in which the mucous membrane was removed. Hexamethonium abolished the effect of substance P on peristalsis. It is concluded that substance P acts on the afferent nervous elements of the peristaltic reflex arc, possibly on the sensory receptors.

Central Nervous System↗