EFFLUXES OF 3,4-DIHYDROXYPHENYLALANINE, 3,4-DIHYDROXYPHENYLGLYCOL, AND NOREPINEPHRINE FROM 4 BLOOD-VESSELS DURING BASAL CONDITIONS AND DURING NERVE-STIMULATION

Effluxes of 3,4-dihydroxyphenylalanine, 3,4-di-hydroxyphenyglycol, and norepinephrine from four superfused canine blood vessels (saphenous a nd portal veins and mesenteric and pulmonary arteries) were studied un der basal conditions and during nerve stimulation. From quantification of the compounds a series of indices of activities al neuroeffector j unctions are proposed. These are (a) basal overflow of 3,4-dihydroxyph enyglycol as an index of vesicular-cytoplasmic translocation of norepi nephrine, (b) the increase in 3,4-dihydroxyphenyglycol overflow attrib utable to nerve stimulation as an index of neuronal reuptake of norepi nephrine released by stimulation, (c) the sum of the increases in over flows of norepinephrine and 3,4-dihydroxyphenylglycol attributable to nerve stimulation as an index of evoked release of norepinephrine, and (d) the efflux of 3,4-dihydroxyphenylalanine as an ind ex of the acti vity of tyrosine hydroxylase, the rate-limiting enzyme in the synthesi s of norepinephrine. There were clear differences between these indice s in the vessels. Correlation coefficients of the indices among vessel s indicated that a high tissue norepinephrine level was associated wit h high biosynthetic capacity and high vesicular-cytoplasmic exchange b ut not with high release. There was no evidence suggesting feedback in hibition of synthesis by neuroplasmic norepinephrine-whether arising f rom vesicular-cytoplasmic translocation or from reuptake from the junc tional cleft. The major value of these indices will probably be in det ermining the integrated effects of pharmacologic agents at neuroeffect or junctions in different blood vessels.