Chronic oral L-DOPA increases dopamine and decreases serotonin excretions

Given the common pathways for uptake and synthesis for dopamine and seroton in, enhanced renal dopamine synthesis in response to increased substrate 3, 4-dihydroxyphenylalanine (L-DOPA) is postulated to decrease renal serotonin synthesis. The present study compared the effects of chronic oral administ ration of L-DOPA on dopamine and serotonin excretion in vivo, with the effe cts of enhanced dopamine synthesis per nephron due to adaptation to reduced renal mass (RRM). Four groups of rats were studied: sham-operated rats and rats with RRM in the absence and presence of chronic oral L-DOPA. L-DOPA ( 2 mg 100 g body wt(-1) day(-1)) for 6-14 days increased calculated dopamine synthesis per nephron in sham-operated rats from 2.0 +/- 0-3 (n = 7) to 13 .6 +/-1.8 pg . day(-1) nephron(-1) (n = 7, P < 0.05) and in rats with RRM f rom 6.1 +/- 1.3 (n = 7) to 39.3 +/- 5.2 pg . day(-1) nephron(-1) (n = 7, P < 0.05). Chronic oral L-DOPA concomitantly decreased serotonin synthesis pe r nephron in sham-operated rats (1.6 +/- 0.1 to 1.0 +/- 0.1 pg day(-1) neph ron(-1), n = 7, P < 0.05) and in rats with RRM (5.6 +/- 0.9 to 2.6 +/- 0.4 pg day(-1) nephron(-1), n = 7, P < 0.05). Both serotonin and dopamine synth esis per nephron were increased in rats with RRM. In conclusion, chronic or al administration of L-DOPA enhances dopamine excretion and decreases serot onin excretion in normal rats and in rats with reduced renal mass. Both dop amine and serotonin excretions per nephron were elevated by renal mass redu ction.