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THE EFFECTS OF INJECTIONS OF d,l ‐5‐HYDROXY‐TRYPTOPHAN ON THE EFFLUX OF ENDOGENOUS SEROTONIN AND 5‐HYDROXYINDOLEACETIC ACID FROM A SYNAPTOSOMAL FRACTION 1
Author(s) -
Penn P. E.,
McBride W. J.
Publication year - 1977
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1111/j.1471-4159.1977.tb10625.x
Subject(s) - 5 hydroxyindoleacetic acid , saline , serotonin , chemistry , tryptophan , potassium , endogeny , medicine , efflux , endocrinology , calcium , biochemistry , amino acid , biology , receptor , organic chemistry
— The effects of i.p. injections of SO mg/kg d,l‐5‐hydroxytryptophan (5‐HTP) and saline alone on the in uitro release of endogenous serotonin (5‐HT) and 5‐hydroxyindoleacetic acid (5‐HIAA) were studied using preparations of axon terminals (P 2 isolated from the telencephalon of rats. The level of 5‐HT was 2‐fold greater and the level of 5‐HIAA was 5‐fold greater in the P 2 fraction isolated from rats given the d,l‐5‐HTP injection than from rats given saline injections. At 37°C the in vitro efflux of 5‐HT and 5‐HIAA from the P 2 fractions of animals injected with 5‐HTP 30min before killing was approx 3 times higher than the saline control group. The amount of 5‐HT and 5‐HIAA released at 37°C was 3–5 times higher than the amount released at 0°C for both the 5‐HTP and saline injected rats. Increasing the concentration of potassium ions in the media to 55 mm significantly increased the release of 5‐HT but not 5‐HIAA in both groups of animals. The amount of 5‐HT released by 55mm‐K + was about 2‐fold higher from the P 2 fraction isolated from rats given 5‐HTP injections with respect to those given saline injections. The potassium stimulated release of 5‐HT was calcium dependent. The data thus indicate that injection of 50 mg/kg d,l‐5‐HTP in rats can cause an increase in the level of 5‐HT and 5‐HIAA in a crude synaptosomal fraction and that as a result of this increase, there is a temperature dependent increased release of 5‐HT and 5‐HIAA under normal resting membrane conditions. There is also an increased release of 5‐HT as a result of membrane depolarizing conditions induced by elevated potassium levels which is calcium dependent.