Immunohistochemical and neurochemical evidence for the presence of serotonin in the adrenal medulla of the rat.
Immunohistochemical and biochemical techniques were used to look for serotonin in the adrenal medulla of the rat. Using antibodies to serotonin, noradrenaline and adrenaline, it could be shown that the adrenaline-storing cells are highly immunoreactive for serotonin. Noradrenaline-storing cells were not stained even after administration of the precursors L-tryptophan and 5-hydroxytryptophan, or of serotonin itself. Specificity of the immune reaction was studied by both absorption and inhibition experiments. Chemical assays showed that rat adrenals contain significant amounts of serotonin (1.4 +/- 0.11 micrograms/g wet weight) which is about 0.4% of the adrenaline levels. Serotonin could be reduced to about 10% of control by a high dose of reserpine. From differential and sucrose gradient centrifugation experiments it was concluded that serotonin is probably stored in granules also containing adrenaline. Administration of 5-hydroxytryptophan led to a marked increase of the serotonin level, preferentially in the granular fraction. This increase could be blocked almost completely by a decarboxylase inhibitor. Serotonin administration did not result in a statistically significant increase of the serotonin concentration. Serotonin levels were not changed either after administration of L-tryptophan or the tryptophan hydroxylase inhibitor H22/54. These results indicate that there is no significant synthesis of serotonin from L-tryptophan. It is suggested that the serotonin present in the adrenaline-storing cells is derived from circulating serotonin and/or 5-hydroxytryptophan. Serotonin taken up directly from the circulation or formed by decarboxylation from 5-hydroxytryptophan is subsequently incorporated in the chromaffin granules.
D000313:Adrenal Medulla / Q000378:metabolism*; D000818:Animals; D004298:Dopamine / Q000378:metabolism; D004837:Epinephrine / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D007124:Immunoenzyme Techniques; D008297:Male; D009638:Norepinephrine / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D012701:Serotonin / Q000378:metabolism*; D013347:Subcellular Fractions / Q000378:metabolism
D012701:Serotonin; D004298:Dopamine; D009638:Norepinephrine; D004837:Epinephrine