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Stimulation of breathing movements by L‐5‐hydroxytryptophan in fetal sheep during normoxia and hypoxia.
Author(s) -
Fletcher D J,
Hanson M A,
Moore P J,
Nijhuis J G,
Parkes M J
Publication year - 1988
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.1988.sp017307
Subject(s) - cyproheptadine , ketanserin , hypoxia (environmental) , stimulation , medicine , endocrinology , serotonin , chemistry , anesthesia , 5 ht receptor , receptor , oxygen , organic chemistry
1. In fetal lambs in late gestation, systemic infusion of L‐5‐hydroxytryptophan (L‐5‐HTP) during normoxia greatly increases the incidence of fetal breathing movements (FBM) and high‐voltage electrocortical activity (HV ECoG). It also induces FBM during HV ECoG and increases blood pressure. To investigate its mechanism of action, L‐5‐HTP was administered in conjunction with the 5‐hydroxy‐tryptamine (5‐HT) antagonists ketanserin or cyproheptadine. L‐5‐HTP was also infused with or without the antagonists during hypoxia, to test whether it would overcome the inhibition of FBM by hypoxia. 2. When L‐5‐HTP was given in normoxia, cyproheptadine blocked and ketanserin reduced the increase in blood pressure, both drugs blocked the stimulation of FBM, but neither drug prevented the induction of prolonged episodes of HV ECoG. 3. In hypoxia, L‐5‐HTP similarly stimulated FBM. This effect was also blocked by cyproheptadine and was delayed by ketanserin. 4. The antagonism of the effects of L‐5‐HTP on blood pressure and the incidence of FBM in normoxia and hypoxia is consistent with the action of L‐5‐HTP via 5‐HT receptors. At present there is no clear explanation of the mechanism by which L‐5‐HTP induces HV ECoG.