Comparison of 3H-norepinephrine and 3H-metaraminol accumulation as indices of adrenergic nerve density in rabbit blood vessels.
The possibility that accumulation of 3H-metaraminol, which is not metabolized, would provide a better estimate of adrenergic nerve density than 3H-norepinephrine accumulation was examined in a series of rabbit blood vessels. Accumulation of 3H-metaraminol was linear for up to 10 min. Norepinephrine accumulation was correlated with metaraminol acumulation in the vessels studied, but the relationship was not a simple one. The findings suggest that, even with short incubation times, metabolism may significantly alter the amount of norepinephrine retained by the tissue. Nevertheless, accumulation of metaraminol was still not well-correlated with endogenous norepinephrine content. Norepinephrine contents of the basilar artery, mesenteric artery and mesenteric vein were quite similar: 2.7, 2.8 and 2.8 micrograms/g respectively. However, values for metaraminol accumulation in these vessels ranged from 8.7 to 1.78 ml cleared/g. These findings suggest that norepinephrine content of a single adrenergic varicosity may vary from tissue to tissue. The relationship between norepinephrine content, storage capacity, uptake activity and transmitter release needs to be more carefully examined. No single parameter can provide an adequate estimate of adrenergic nerve density.
D000320:Adrenergic Fibers / Q000033:anatomy & histology / Q000378:metabolism*; D000818:Animals; D001808:Blood Vessels / Q000294:innervation* / Q000378:metabolism; D005260:Female; D066298:In Vitro Techniques; D008297:Male; D008680:Metaraminol / Q000378:metabolism*; D009638:Norepinephrine / Q000378:metabolism*; D011817:Rabbits
D008680:Metaraminol; D009638:Norepinephrine