Garcia, Nestor Horacio

Given the common pathways for uptake and synthesis for dopamine and serotonin, 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 administration ofl-DOPA on dopamine and serotonin excretion in vivo, with the effects 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 orall-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 from 6.1 ± 1.3 ( n = 7) to 39.3 ± 5.2 pg ⋅ day−1⋅ nephron−1( n = 7, P < 0.05). Chronic orall-DOPA concomitantly decreased serotonin synthesis per nephron in sham-operated rats (1.6 ± 0.1 to 1.0 ± 0.1 pg ⋅ day−1⋅ nephron−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 synthesis per nephron were increased in rats with RRM. In conclusion, chronic oral administration ofl-DOPA enhances dopamine excretion and decreases serotonin excretion in normal rats and in rats with reduced renal mass. Both dopamine and serotonin excretions per nephron were elevated by renal mass reduction.

Fluid and solute reabsorption by the proximal tubule is the result of both transcellular and paracellular flux. The role of transcellular transport has been extensively studied, but the importance of paracellular flux has not been as thoroughly investigated. The purpose of this review is to update concepts about the contribution of paracellular transport for reabsorption by the proximal tubule.