HIGHER DOPAMINE LEVEL IN LYMPH FROM THE CERVICAL LYMPH TRUNK THAN IN PLASMA FOLLOWING INTRAVENOUS BOLUS INJECTION OF L-DOPA IN RATS

To clarify the mechanism(s) responsible for nausea and vomiting induce d by L-dopa administration, dopamine levels in the plasma and lymph of rats were investigated in the 60-min period following an intravenous bolus of L-dopa (2.5 mg/kg body weight). The dopamine level in plasma from the femoral artery was the highest at 5 min immediately after the L-dopa injection, and was eliminated thereafter. Shelving the same te ndency as the plasma, the lymph from the thoracic duct showed a maxima l increase of dopamine at 0 to 10 min, and a rapid decrease later. In contrast, the dopamine level in the lymph from the cervical lymph trun k increased, peaked at 10 to 20 min, and fell gradually thereafter. Th e dopamine level in the cervical lymph was higher than that in the tho racic lymph. When these data were kinetically analyzed, the cervical l ymph had a larger area under the dopamine concentration-time curve tha n the thoracic lymph. Both the cervical lymph and the thoracic lymph h ad longer values of dopamine mean residence time than the plasma. Our findings revealed that when L-dopa was administered with an intravenou s bolus, dopamine was higher and remained longer in the cervical lymph than in the rest of the body.