A tritium-release in vivo assay of dopamine-β-hydroxylase activity in sympathetic neurons

Abstract

Measurement of the rate of release in vivo of tritium from [β- 3H]dopamine is proposed as an index of dopamine-β-hydroxylase activity in sympathetic neurons. After the systemic administration of this labeled compound to rats, the accumulation of tritium in body water is roughly linear with time and is partially inhibited by pretreatment of the animals with the dopamine-β-hydroxylase inhibitors, disulfiram and fusaric acid. Pretreatment of the animals with the monoamine oxidase inhibitor, tranylcypromine, alters neither the rate of tritiated water accumulation nor the extent to which this rate is slowed by the dopamine-β-hydroxylase inhibitors. The tritium-release assay has been tested in animals subjected to experimental protocols known to alter the levels of dopamine-β-hydroxylase in sympathetic neurons. Chemical sympathectomy with 6-hydroxydopamine, which leads to a decrease in dopamine-β-hydroxylase activity in tissue extracts, decreased the rate of tritiated water release in vivo. Chronic exposure of animals to cold, which leads to an increase in dopamine-β-hydroxylase activity in tissue extracts, increased the rate of tritiated water release in vivo. Furthermore, this effect of cold stress is prevented by dopamine-β-hydroxylase inhibitors. Our data thus suggest that accumulation of tritiated water in the whole animal after the administration of [β- 3H]dopamine can be used as an index of dopamine-β-hydroxylase activity in sympathetic neurons.