DIFFERENTIATION OF NOREPINEPHRINE STORAGE COMPARTMENTS IN PERIPHERAL ADRENERGIC NERVES

¹ Department of Pharmacology, Oakdale Toxicology Center, College of Medicine, University of Iowa, Oakdale, Iowa

The true distribution of norepinephrine (NE) between particulate and "free" cytoplasmic sites in adrenergic nerves is not known for any tissue. The fluorescence histochemical procedure of Falck and Hillarp has been assumed to detect total NE, most of which was considered to be particulate and associated with granular synaptic vesicles. On the basis of previous studies we formulated the hypothesis that extravesicular (free) NE was detected preferentially by fluorescence histochemistry. To test this hypothesis catecholamine biosynthesis was inhibited by treatment of rats with -methyl-p-tyrosine, and the iris and vas deferens were examined at various times after treatment to determine whether there was a difference in the disappearance of NE as visualized by fluorescence histochemistry and by electron microscopy. In the iris catecholamine histochemical fluorescence, granular vesicles and NE content all declined promptly after -methyl-p-tyrosine treatment. The vas deferens showed an equally rapid loss of histochemical fluorescence to about 25% of normal, but there was no decrease in the proportions of granular vesicles at any time studied; NE content was decreased initially, followed by a partial restoration. Thus, the fluorescence histochemical procedure appeared to detect a storage form of NE which was different from that demonstrated by electron microscopy in the vas deferens. The more fluorescent NE was presumed to be extravesicular, but a nonelectron-opaque vesicular form of NE could not be excluded. The experiment was complicated by unexpectedly large amounts of -methyl-NE formed from -methyl-p-tvrosine.