Differential effect of guanethidine on dopamine and norepinephrine in rat peripheral tissues

The changes of dopamine (DA) and norepinephrine (NE) were investigated in rat peripheral tissues after guanethidine treatment (50 mg/kg i.p. five days each week) during one week (group 1, n = 10, five injections) and during 2.5 weeks (group 2, n = 8, 13 injections). Guanethidine greatly reduced NE levels in all the analyzed tissues but only partially depleted DA in kidney, bladder, stomach, intestine, lung and liver and in sympathetic ganglia. The differential pattern of changes between DA and NE induced by guanethidine suggests that peripheral DA is distributed in several neuronal or non-neuronal pools, whose presence, nature and contribution varies in the different tissues. Both noradrenergic cell bodies and small intensely fluorescent cells (SIF cells) can contribute to the DA in the superior cervical ganglion. Noradrenergic neurons seem to be the main sources of DA in seminal vesicles, vas deferens, heart and spleen. In addition to noradrenergic nerves, extraneuronal sources could account for a meaningful portion of DA in kidney, gastrointestinal tract, lung and liver. The bladder is the peripheral tissue where DA exhibits the highest resistance to the neurotoxin. Accordingly, these tissues may provide meaningful sources of non-precursor DA pools.