Enhancement of 5‐Hydroxytryptamine Uptake in Rabbit Hypothalamic Synaptosomes but not in Blood Platelets by Zinc and Lead ex Vivo

Lead (0.2%), zinc (0.5%) or their combination was given to rabbits as acetate salts in drinking water for 2 or 4 weeks. Cerebral Pb increased within exposure time but the increase of Zn was marginal when given alone. After combination of Pb + Zn, blood Pb increased but Zn decreased as compared to the administration of the single metal alone. Concurrently brain Pb increased but remained at a lower level as compared with sole Pb administration while brain Zn did not differ from controls. The uptake of 5-hydroxytryptamine (5-HT) into hypothalamic synaptosomes increased 70-85% with Pb, Zn and Pb + Zn after 2 weeks and 93% with Zn and 76% with Pb + Zn after 4 weeks. Dopamine uptake into striatal synaptosomes did not change. Zn decreased endogenous noradrenaline concentrations by 21% and Pb + Zn that of 5-HT by 36% in the striatum. Pb + Zn decreased cortical dopamine concentrations by 26%. Concurrently, 5-HT uptake in blood platelets, platelet numbers and their content of endogenous 5-HT did not change significantly. These results indicate that high Zn and Pb have parallel effects on 5-HT uptake in hypothalamic synaptosomes and their combination may be neurochemically more toxic than the individual metals. The increase of 5-HT uptake in hypothalamic synaptosomes but not in blood platelets requires further methodological work to explain the differences between synaptosomes and platelets.