Effects of substance P on carotid chemoreceptor activity in the cat.

Abstract

SUMMARY1. The influence of substance P (SP) on spontaneous chemosensory discharge and on responses of the carotid chemoreceptors to various drugs has been investigated in pentobarbitone anaesthetized cats in which chemoreceptor activity was recorded from the peripheral end of a sectioned sinus nerve.2. After an initial slight inhibition during the first 5-15 see following the injection, SP (0.1-100 j#g I.A.) caused a dose-related increase in discharge which lasted for 45-300 see in artificially ventilated cats, discharge being increased by about 50 % on average. The increase was of shorter duration when the animals were allowed to breathe spontaneously. 3. The delayed increase in discharge was not secondary to the hypotension caused by SP, nor was it entirely due to changes in bronchomotor tone resulting from direct or indirect actions of SP, although such changes contributed to the response. It was not possible to determine whether the excitation was due to a direct effect of SP on the chemoreceptors.4. Chemosensory excitation evoked by NaCN (5 ,ag I.A.) was potentiated during I.A. infusions of SP and also 10-20 min after SP (10 jagtl.A.) had been injected. In contrast, responses to ACh (50 jag I.A.) were inhibited. These effects may be due to a nicotinic-blocking action of SP on the carotid chemoreceptors. It was also found that the inhibitory action of dopamine (5 jag I.A.) was reduced during SP infusion whereas that of 5-HT (10 jag I.A.) was potentiated.5. A sample of crude SP had effects on spontaneous chemoreceptor discharge and responses to NaCN and ACh which were qualitatively similar to those obtained using synthetic SP.6. The physiological significance of the results is discussed and it is concluded that the interpretation depends upon whether or not SP is present in the cat's carotid body.

Peripheral Chemoreceptors: Function and Plasticity of the Carotid Body

“…Exogenous administration of SP augments the sensory discharge of the carotid body in a number of species (175, 472, 570, 595, 721) with the exception of goats (707). SP potentiates the hypoxic sensory response (721) and, whereas SP receptor antagonists, when given in nanomolar concentrations, prevent the excitatory effects of SP, and abolish the sensory response to hypoxia while leaving the sensory response to hypercapnia unaffected in cats (718, 722, 726) as well as in rats (175).…”

Effects of Putative Neurotransmitters of the Carotid Body on its Own Glomus Cells

“…The predominant effect is sensory discharge depression, but this is followed by a rebound to above normal values (Docherty and McQueen, 1979;Monti-Bloch and Eyzaguirre, 1980). The variable actions of met-enkephalin and substance P on the glomus cell membrane are more in line with their effects on the sensory discharge of the cat carotid nerve (McQueen, 1980;McQueen and Ribeiro, 1980;Monti-Bloch and Eyzaguirre, 1985). There is no information on the effects of cholinergic agents on the mouse carotid nerve or on the effects of peptides on rabbit and mouse chemosensory discharges.…”

Effects of Β‐endorphin, Vasoactive Intestinal Polypeptide and Cholecystokinin Octapeptide on Cat Carotid Chemoreceptor Activity

“…The ability of some polypeptides to modify spontaneous chemoreceptor discharge when injected close-arterial to the cat carotid body has been described (McQueen, 1979(McQueen, , 1980. Since then evidence has been presented which shows that substance P (SP), the enkephalins and vasoactive intestinal polypeptide (VIP), or closely related immunoreactive substances, are present in the cat carotid body (Lundberg, Hokfelt, Fahrenkrug, Nilsson & Terenius, 1979;Cuello & McQueen, 1980;Wharton, Polak, Pearse, McGregor, Bryant, Bloom, Emson, Bisgard & Will, 1980).…”