Dopamine DA1 receptor agonist, fenoldopam, reverses glycine-induced hyperfiltration in rats

Dopamine D1 receptor (DRD1) genetic polymorphism: pleiotropic effects on heritable renal traits

Because dopamine D(1) receptors (DRD1) influence renal sodium transport and vascular hemodynamics, we examined whether genetic polymorphisms play a role in renal function. We conducted polymorphism discovery across the DRD1 open reading frame and its 5'-UTR and then performed association studies with estimated glomerular filtration rate (eGFR), plasma creatinine (pCr), and fractional excretion of uric acid (FeUA). We used a twin/family group of 428 subjects from 195 families and a replication cohort of 677 patients from the Kaiser health-care organization sampled from the lower percentiles of diastolic blood pressures. Although the coding region lacked common non-synonymous variants, we identified two polymorphisms in the DRD1 5'-UTR (G-94A, A-48G) that occurred with frequencies of 15 and 30%, respectively. In the twin/family study, renal traits were highly heritable, such that DRD1 G-94A significantly associated with eGFR, pCr, and FeUA. Homozygotes for the G-94A minor allele (A/A) exhibited lower eGFR, higher pCr, and lower FeUA. No effects were noted for DRD1 A-48G. Patients in the Kaiser group had similar effects of G-94A on eGFR and pCr. Kidney cells transfected with the -94A variant but not the wild type vectors had increased receptor density. Because the -94A allele is common and may reduce glomerular capillary hydrostatic pressure, G-94A profiling may aid in predicting survival of renal function in patients with progressive renal disease.

Renal dopamine receptor function in hypertension

Dopamine plays an important role in the regulation of renal sodium excretion. The synthesis of dopamine and the presence of dopamine receptor subtypes (D1A, D1B, as D1-like and D2, and D3 as D2-like) have been shown within the kidney. The activation of D1-like receptors located on the proximal tubules causes inhibition of tubular sodium reabsorption by inhibiting Na,H-exchanger and Na,K-ATPase activity. The D1-like receptors are linked to the multiple cellular signaling systems (namely, adenylyl cyclase, phospholipase C, and phospholipase A2) in the different regions of the nephron. Defective renal dopamine production and/or dopamine receptor function have been reported in human primary hypertension as well as in genetic models of animal hypertension. There may be a primary defect in D1-like receptors and an altered signaling system in the proximal tubules that lead to reduced dopamine-mediated effects on renal sodium excretion in hypertension. Recently, it has been shown in animal models that the disruption of either D1A or D3 receptors at the gene level causes hypertension in mice. Dopamine and dopamine receptor agonists also provide therapeutic potential in treatment of various cardiovascular pathological conditions, including hypertension. However, because of the poor bioavailability of the currently available compounds, the use of D1-like agonists is limited to the management of patients with severe hypertension when a rapid reduction of blood pressure is clinically indicated and in acute management of patients with heart failure. In conclusion, there is convincing evidence that dopamine and dopamine receptors play an important role in regulation of renal function, suggesting that a defective dopamine receptor/signaling system may contribute to the development and maintenance of hypertension. Further studies need to be directed toward establishing a direct correlation between defective dopamine receptor gene in the kidney and development of hypertension. Subsequently, it may be possible to use a therapeutic approach to correct the defect in dopamine receptor gene causing the hypertension.

Regional haemodynamic effects of dopamine and its prodrugs L-dopa and gludopa in the rat and in the glycerol-treated rat as a model for acute renal failure

1. In this study the renal selectivity of dopamine and its prodrugs L-dopa and gludopa, with respect to their effects on regional blood flow, vascular resistance and central haemodynamics was investigated in normal rats and in rats with glycerol-induced acute renal failure (ARF). 2. In normal, anaesthetized rats, dopamine as well as its prodrugs caused a dose-dependent reduction of vascular resistance in the kidney (RR), mesentery (MR) and hindquarters (HQR) (dose range: dopamine: 0.1-5 mumol kg-1 h-1; L-dopa and gludopa: 1-200 mumol kg-1 h-1). Blood pressure and heart rate were affected at the highest dose only. 3. Administration of glycerol induced a preferential renal vasoconstriction; renal blood flow (-60%) and vascular resistance (+190%) were significantly more affected than MR (+40%) and HQR (+60%). This was only ameliorated by a low rate (10 mumol kg-1 h-1) infusion of gludopa: the glycerol-induced reduction of renal flow and increase in RR were significantly attenuated. A high dose of gludopa (100 mumol kg-1 h-1) or any dose of L-dopa or dopamine did not induce this beneficial effect. The glycerol-induced increase in MR and HQR was not attenuated by any of the treatments used. 4. The results indicate that gludopa is not renally selective at a pharmacodynamic level in normal, anaesthetized rats. Contrary to this, a low dose of gludopa does cause a renal selective vasodilatation and reduction of RR in rats with glycerol-induced ARF. This difference could be explained by a difference in renal vascular tone between normal rats and glycerol-induced ARF rats. A high dose ofgludopa does not cause these renal-selective effects: renal resistance and renal flow are at the same level as following glycerol and saline. This is probably due to the systemic effects of the released dopamine.

Pregnancy restores the renal vasodilator response to glycine in Dahl salt-sensitive rats

To determine if pregnancy alters the impaired renal vasodilator responses in hypertensive Dahl salt-sensitive (Dahl S) rats, we measured glomerular filtration rate and effective renal plasma flow and calculated renal vascular resistance before, during, and after renal vasodilation with glycine (0.17 mmol/kg per minute IV). Conscious, midterm (day 11 to 14) pregnant and age-matched virgin Dahl S and Dahl salt-resistant (Dahl R) rats were fed an 8% NaCl diet for 4 weeks (n = 6 per group). Mean arterial pressure was elevated (P < .05) in Dahl S compared with Dahl R rats, with no significant difference between pregnant and virgin animals in either group. Pregnancy resulted in significant increases in plasma volume, baseline glomerular filtration rate, and renal plasma flow and a significant decrease in renal vascular resistance. The glycine-induced increase in filtration rate in virgin Dahl S rats (27 +/- 4%) was less (P < or = .01) than pregnant Dahl S (60 +/- 4%) and either group of Dahl R (virgin, 43 +/- 3%; pregnant, 45 +/- 5%) rats. Similarly, the 21 +/- 4% increase in renal plasma flow in virgin Dahl S rats was less (P < or = .01) than the pregnant Dahl S (45 +/- 4%) and either pregnant (45 +/- 5%) or virgin (45 +/- 5%) Dahl R rats. Glycine decreased renal vascular resistance only 12 +/- 2% in the virgin Dahl S compared with 31 +/- 3% in the pregnant Dahl S rats and 30 +/- 4% and 28 +/- 3% in pregnant and virgin Dahl R rats.(ABSTRACT TRUNCATED AT 250 WORDS)