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THE ACTION OF 5‐HYDROXYTRYPTAMINE ON CHEMORECEPTOR DISCHARGES OF THE CATS CAROTID BODY
Author(s) -
NISHI K.
Publication year - 1975
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1975.tb07606.x
Subject(s) - chemoreceptor , carotid body , atropine , methysergide , hexamethonium , chemistry , baroreceptor , reserpine , cats , medicine , endocrinology , anesthesia , carotid sinus , acetylcholine , serotonin , electrophysiology , heart rate , reflex , receptor , blood pressure
1 Chemoreceptor discharges were recorded in vivo from fine filaments of the carotid sinus nerve containing a single or several active units; their frequency was used as an index of receptor activity. The effects of 5‐hydroxytryptamine (5‐HT) on chemoreceptors were studied in 26 adult cats. At times, sinus baroreceptor discharges were recorded from the carotid nerve and the effect of 5‐HT on the discharges was examined. 2 Intra‐carotid injections of 5‐HT (2–20 μg) induced a sharp and brief increase in chemoreceptor discharges, followed by depression or block which lasted for several seconds. Repeated injections at short intervals, and a small dose after a large dose of 5‐HT resulted in depressed or blocked response to 5‐HT. 3 5‐HT in high doses (10–20 μg, La.) slightly depressed the chemoreceptor discharges induced by either acetylcholine (ACh) or NaCN, when these substances were applied within 20 s after 5‐HT. 5‐HT (5–20 μg, i.a.) applied during asphyxia induced a further increase in chemoreceptor discharges, soon followed by block of the discharges lasting for several seconds. 4 Atropine or hexamethonium in high doses did not change the chemoreceptor response to 5‐HT, while that to ACh was markedly depressed. 5 (+)‐Lysergic diethylamide (LSD), methysergide or gramine did not alter the response to 5‐HT, while LSD in low doses produced a marked increase in chemoreceptor discharges. 6 Acute and chronic treatment with reserpine (5–10 mg/kg, i.v.) of the animals did not change the sensitivity and the reactivity of the chemoreceptor to ACh and NaCN, while the chemoreceptor response to 5‐HT was augmented, indicating an increase in the sensitivity of chemoreceptors to 5‐HT. 7 5‐HT in small doses (2–10 μg, i.a.) induced a marked increase in sinus baroreceptor discharges; subsequently discharges were depressed or blocked for several seconds. 8 The results are discussed in relation to possible mechanism of action of 5‐HT on the chemoreceptors. It is concluded that the exogenous 5‐HT probably acts directly on the chemosensory nerve endings and depolarizes them, but 5‐HT contained in the carotid body does not play a significant role in the generation of chemoreceptor discharges.