5-Hydroxytryptamine in the phrenic nerve diaphragm: evidence for its existence and release.
Evidence is presented for the existence of 5-hydroxytryptamine (5-HT) within the phrenic nerve of the rat and its release following electrical stimulation. Contents of 5-HT and its metabolite, 5-hydroxyindoleacetic acid (5-HIAA) in the phrenic nerve and the indoleamine released into the bathing fluid were estimated fluorimetrically after isolation on Sephadex G-10 and/or solvent-solvent extraction. Bioassays of 5-HT were done on rat fundus strip. The phrenic nerve and the end-plate zone contains high levels of 5-HT (1.9 micrograms/g wet weight) and 5-HIAA (1.5 micrograms/g wet weight). The resting release of around 1 ng 5-HT/diaphragm/min was enhanced by 50% (1.5 ng 5-HT/diaphragm/min) upon supramaximal (2-4 V) electrical stimulation of 5 Hz. Phrenic nerve diaphragm prepared from the denervated and p-chlorophenylalanine (300 mg/kg/day i.p. for 3 days) treated rats failed to release 5-HT confirming the neuronal origin and the identity of the indoleamine respectively. Furthermore, methysergide, an antagonist of 5-HT in rat fundus strip, blocked the response obtained by the sample on it. A modulatory role of 5-HT in the phrenic nerve diaphragm of the rat is envisaged from the present study.
Das
M
M
Division of Pharmacology and Experimental Therapeutics, Indian Institute of Chemical Biology, Jadavpur.
Mohanakumar
K P
KP
Chauhan
S P
SP
Ganguly
D K
DK
D000818:Animals; D003714:Denervation; D004558:Electric Stimulation; D005260:Female; D010134:Fenclonine / Q000378:metabolism; D007734:Kymography; D008297:Male; D010791:Phrenic Nerve / Q000378:metabolism* / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013050:Spectrometry, Fluorescence
D012701:Serotonin; D010134:Fenclonine