The dopamine prodrug, gludopa, decreases both renal and extrarenal noradrenaline spillover in conscious rabbits

The Role of the Renal Dopaminergic System and Oxidative Stress in the Pathogenesis of Hypertension

The kidney is critical in the long-term regulation of blood pressure. Oxidative stress is one of the many factors that is accountable for the development of hypertension. The five dopamine receptor subtypes (D₁R–D₅R) have important roles in the regulation of blood pressure through several mechanisms, such as inhibition of oxidative stress. Dopamine receptors, including those expressed in the kidney, reduce oxidative stress by inhibiting the expression or action of receptors that increase oxidative stress. In addition, dopamine receptors stimulate the expression or action of receptors that decrease oxidative stress. This article examines the importance and relationship between the renal dopaminergic system and oxidative stress in the regulation of renal sodium handling and blood pressure. It discusses the current information on renal dopamine receptor-mediated antioxidative network, which includes the production of reactive oxygen species and abnormalities of renal dopamine receptors. Recognizing the mechanisms by which renal dopamine receptors regulate oxidative stress and their degree of influence on the pathogenesis of hypertension would further advance the understanding of the pathophysiology of hypertension.

Preferential release of renal dopamine into the tubule lumen: effect of chronic sodium loading

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.28% NaCl, NS) or high (4.0% NaCl, HS) sodium balance (n = 9 in each group). Urine flow (UV) and sodium excretion (UNaV) in HS were greater than in NS rats (UV 7.2 +/- 0.6 vs 3.8 +/- 0.3 microliters/min, P < 0.01; UNaV 497 +/- 66 vs 265 +/- 27 nmol/min, P < 0.01). In rats on both NS and HS balance, UDAV was significantly higher than RIF DA (420 +/- 37 vs 3.68 +/- 0.49 pg/min in the NS rat; 601 +/- 68 vs 1.25 +/- 0.36 pg/min in the HS rat, both P < 0.01). UDAV was increased in HS compared with NS rats (601 +/- 68 vs 420 +/- 37 pg/min, P < 0.05). In contrast, RIF DA was significantly lower in HS than NS rats (1.25 +/- 0.36 vs 3.68 +/- 0.49 pg/min, P < 0.01). In conclusion, chronic sodium loading increased renal DA production and release predominantly into the tubular lumen rather than the peritubular interstitial space of the kidney. These results indicate that DA originating from proximal tubule cells has a direct tubule action in the control of sodium excretion.

Intrarenal dopamine production and distribution in the rat. Physiological control of sodium excretion

Dopamine (DA), produced by the renal proximal tubule, has been demonstrated as an intrarenal paracrine hormone mediating diuresis and natriuresis. The precise mechanism by which DA exerts its cell-to-cell action is not fully understood. In the present study, renal interstitial fluid (RIF) DA (by in vivo microdialysis) and urinary DA excretion (UDAV) were compared in anesthetized rats on either normal (0.28% NaCI, NS) or high (4.0% NaCI, HS) sodium balance and in response to acute gamma-L-glutamyl-L-dopa (gludopa) administration. Urine flow (UV) and sodium excretion (UNaV) in HS were greater than in NS rats. UDAV was increased in HS compared with NS rats. RIF DA was significantly lower in HS than NS rats. Gludopa at 3, 5, and 7.5 nmol/kg (IV bolus) produced a larger increase in UDAV than RIF DA. Only the highest dose of gludopa (7.5 nmol/kg), which resulted in a 7.3-fold increase in UDAV and 1.7-fold increase in RIF DA, was associated with significant diuresis and natriuresis. Cortical and medullary blood flow remained unchanged after gludopa (7.5 nmol/kg) administration, while angiotensin II (100 ng.kg-1.min-1) induced significant reduction in cortical and medullary blood flow. Prior bilateral renal denervation did not have a significant effect on basal DA levels (RIF DA and UDAV) or gludopa-induced DA production or natriuresis and diuresis. These data demonstrated that both chronic sodium loading and acute gludopa administration stimulated renal DA production and release predominantly into the tubule lumen, where DA had a direct tubule action in the control of UNaV. Renal DA production and its renal effects were not significantly regulated by renal sympathetic nerve activity.

Effects of isotonic saline loading on renal tubular and neurogenic dopamine release in conscious rabbits

1. This study was designed to investigate the effects of isotonic saline loading on renal tubular and neurogenic dopamine (DA) in conscious rabbits. 2. Isotonic saline loading did not affect mean arterial pressure, heart rate or renal blood flow but markedly increased urine volume, sodium excretion and DA excretion. 3. Renal DA spillover was not affected by venous emptying, while renal noradrenaline (NA) spillover tended to decrease during saline loading. The ratio of % renal DA spillover to % renal NA spillover increased to 2.3 +/- 0.6 (P < 0.05) 3 h after saline loading. 4. Isotonic saline loading increased renal tubular DA production but had little effect on neurogenic DA release.