Dopamine-1 receptor coupling defect in renal proximal tubule cells in hypertension

Renal dopaminergic mechanisms in renal parenchymal diseases, hypertension, and heart failure

The recovery of renal function in renal transplant recipients is accompanied by an enhanced ability to synthesize dopamine (DA), which may contribute to maintain sodium homeostasis. Patients suffering from chronic renal parenchymal disease, a well-recognized form of salt sensitive (SS) hypertension, have a reduced ability to produce DA that correlates well with deterioration of renal function. In patients afflicted with IgA nephropathy, but normal renal function, urinary excretion of DA correlated positively with BP responses to changes from 200 to 20 mmol/day salt intake. In black salt resistant (SR) normotensives (NT) and SR hypertensives, under low salt intake (40 mmol/day), but not SS-NT and SS-HT, the saline infusion induced increments of DA and DOPAC urinary excretion correlated significantly with increments of sodium urinary excretion and sodium fractional excretion. Patients afflicted with heart failure (HF) have a reduced delivery of L-DOPA to the kidney, accompanied by an increase in DA/L-DOPA urinary ratios. This suggests that HF patients have an increased ability to take up or decarboxylate L-DOPA. Sodium restriction resulted in a significant decrease in urinary L-DOPA, DA and DOPAC in HF patients, suggesting that the system responds to sodium. It is concluded that activity of renal dopaminergic system may be altered in SS subjects, despite the level of their BP, and an enhanced delivery of L-DOPA to the kidney may be beneficial in edema formation states.

Renal dopamine and sodium homeostasis

During the past decade, it has become evident that dopamine plays an important role in the regulation of fluid and electrolyte balance and blood pressure. Dopamine exerts its actions through two families of dopamine receptors, designated D1-like and D2-like, which are identical in the brain and in peripheral tissues. The two D1-like receptors--D1 and D5 receptors--expressed in mammals are linked to stimulation of adenylyl cyclase. The three D2-like receptors--D2, D3, and D4,--are linked to inhibition of adenylyl cyclase. Dopamine affects fluid and electrolyte balance by regulation of renal excretion of electrolytes and water through actions on renal hemodynamics and tubular epithelial transport and by modulation of the secretion and/or action of vasopressin, renin, aldosterone, catecholamines, and endothelin B receptors (ETB) receptors. It also affects fluid and sodium intake by way of "appetite" centers in the brain and alterations of gastrointestinal tract transport. The production of dopamine in neural and non-neural tissues and the presence of receptors in these tissues suggest that dopamine can act in an autocrine or paracrine fashion. This renal autocrine-paracrine function, which becomes most evident during extracellular fluid volume expansion, is lost in essential hypertension and in some animal models of genetic hypertension. This deficit may be caused by abnormalities in renal dopamine production and polymorphisms or abnormal post-translational modification and regulation of dopamine receptor subtypes.

Molecular mechanisms of sodium transport inhibition in proximal tubule during acute hypertension

Acute hypertension provokes a rapid decrease in proximal tubule salt and water reabsorption that increases the levels of sodium chloride at the macula densa, the error signal to increase arteriolar resistance to autoregulate renal blood flow and glomerular filtration rate, and contributes to pressure natriuresis. The molecular mechanisms responsible for this critical homeostatic adjustment are beginning to be dissected: apical sodium transporters in the proximal tubule are redistributed out of the brush border to intermicrovillar and endosomal stores and sodium pump activity is inhibited. These responses are strikingly similar to the cellular responses to parathyroid hormone, and are mediated by similar signalling pathways.

Defective renal dopamine D1-like receptor signal transduction in obese hypertensive rats

It is reported that dopamine promotes renal sodium excretion via activation of D1-like dopamine receptors located on the proximal tubules. In spontaneously hypertensive rats the natriuretic and diuretic response to exogenously administered and endogenously produced dopamine is reduced, which results from a diminished dopamine-induced inhibition of the enzyme, Na+,K+-ATPase. The present study was designed to examine dopamine-receptor mediated inhibition of Na+,K+-ATPase and its associated signal transduction pathway in the proximal tubules of Zucker obese and lean control rats. The obese animals were hypertensive, hyperinsulinaemic and hyperglycaemic compared with the lean rats. While dopamine caused inhibition of Na+,K+-ATPase activity in lean rats, this effect was significantly attenuated in the obese animals. There was significant reduction in D1-like receptor numbers in the basolateral membranes of obese rats compared with lean rats with no change in the affinity to the ligand [3H]SCH 23390 between the two groups of rats. Dopamine failed to stimulate G proteins as measured by [35S]GTPgammaS binding in the obese rats. Also, dopamine was unable to cause phospholipase-C activation in obese rats, but it did activate phospholipase-C in lean rats. These results show that reduction in D1-like receptor numbers and a defect in receptor-G protein coupling may account for the inability of dopamine to activate the D1-like receptor-coupled signal transduction pathway and cause inhibition of Na+,K+-ATPase in the obese hypertensive rats.

Intrarenal dopamine coordinates the effect of antinatriuretic and natriuretic factors

The precision by which sodium balance is regulated suggests an intricate interaction between modulatory factors released from intra- and extrarenal sources. Intrarenally produced dopamine has a central role in this interactive network. Dopamine, produced in renal tubular cells acts as an autocrine and paracrine factor to inhibit the activity of Na+,K+-ATPase as well as of a number of sodium influx pathways. The natriuretic effect of dopamine is most prominent under high salt diet. The antinatriuretic effects of noradrenaline, acting on alpha-adrenoceptors and angiotensin II are opposed by dopamine as well as by atrial natriuretic peptide (ANP). Several lines of evidence have suggested that ANP acts via the renal dopamine system and recent studies from our laboratory have shown that this effect is attributed to recruitment of silent D1 receptors from the interior of the cell towards the plasma membrane. Taken together, the observations suggest that dopamine coordinates the effects of antinatriuretic and natriuretic factors and indicate that an intact renal dopamine system is of major importance for the maintenance of sodium homeostasis and normal blood pressure.

D1 dopamine receptor signalling defect in spontaneous hypertension

Dopamine modulates cardiovascular function by actions in the central and peripheral nervous system, by altering the secretion/release of prolactin, pro-opiomelanocortin, vasopressin, aldosterone, and renin, and by directly affecting renal function. Dopamine produced by the renal proximal tubule exerts an autocrine/paracrine action via two classes of dopamine receptors, D1-like (D1 and D5) and D2-like (D2, D3, and D4), that are differentially expressed along the nephron. The autocrine/paracrine function of dopamine, manifested by tubular rather than by haemodynamic mechanisms, becomes most evident during extracellular fluid volume expansion. This renal autocrine/paracrine function is lost in essential hypertension and in some animal models of genetic hypertension. The molecular basis for the dopaminergic dysfunction in hypertension may involve an abnormal post-translational modification of dopamine receptors.