Abstract
Granular vesicles, about 500 Å in diameter, occur characteristically in the terminals of sympathetic nerves. The possible localization of norepinephrine and serotonin within these vesicles is investigated in the rat pineal, where these two amines are known to occur. The distribution of granular vesicles in sympathetic nerves has been manipulated with drugs, the effects of which are evaluated electron microscopically by all-or-none responses. Metaraminol, in doses varying from 8.0 to 025 mg/kg, was administered to adult female Spraque-Dawley rats. To other animals, pretreated with 2.0 mg/kg of metaraminol, norepinephrine bitartrate (1.0 mg/kg) or L-tryptophan (50-200 mg/kg) was given. The pineal bodies of these animals were fixed by immersion in barbital-buffered osmium tetroxide and examined electron microscopically. The administration of metaraminol, in a dose of at least 2.0 mg/kg, was associated with the total depletion of 500-Å granular vesicles. In animals pretreated with metaraminol, the administration of norepinephrine was associated with repletion of granular vesicles, while the administration of tryptophan appeared ineffectual. Since metaraminol is not osmiophilic, it is probable that it replaces norepinephrine in the granular vesicles and is replaced itself by exogenous norepinephrine. These data indicate that granular vesicles normally contain norepinephrine, which is bound specifically to the approximately 200-Å granule of the vesicle. It is suggested that the latter may be termed appropriately a "norepinephrine storage vesicle."
Footnotes
- Accepted February 3, 1966.
- The Williams & Wilkins Comapny
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