Binding of losartan to angiotensin AT1 receptors increases dopamine D1 receptor activation.

Signaling through both angiotensin AT1 receptors (AT1R) and dopamine D1 receptors (D1R) modulates renal sodium excretion and arterial BP. AT1R and D1R form heterodimers, but whether treatment with AT1R antagonists functionally modifies D1R via allosterism is unknown. In this study, the AT1R antagonist losartan strengthened the interaction between AT1R and D1R and increased expression of D1R on the plasma membrane in vitro. In rat proximal tubule cells that express endogenous AT1R and D1R, losartan increased cAMP generation. Losartan increased cAMP in HEK 293a cells transfected with both AT1R and D1R, but it did not increase cAMP in cells transfected with either receptor alone, suggesting that losartan induces D1R activation. Furthermore, losartan did not increase cAMP in HEK 293a cells expressing AT1R and mutant S397/S398A D1R, which disrupts the physical interaction between AT1R and D1R. In vivo, administration of a D1R antagonist significantly attenuated the antihypertensive effect of losartan in rats with renal hypertension. Taken together, these data imply that losartan might exert its antihypertensive effect both by inhibiting AT1R signaling and by enhancing D1R signaling.

Prolactin and dopamine 1-like receptor interaction in renal proximal tubular cells.

Prolactin is a natriuretic hormone and acts by inhibiting the activity of renal tubular Na(+)-K(+)-ATPase activity. These effects require an intact renal dopamine system. Here, we have studied by which mechanism prolactin and dopamine interact in Sprague-Dawley rat renal tissue. Na(+)-K(+)-ATPase activity was measured as ouabain-sensitive ATP hydrolysis in microdissected renal proximal tubular segments. Intracellular signaling pathways were studied by a variety of different techniques, including Western blotting using phosphospecific antibodies, immunoprecipitation, and biotinylation assays. We found that dopamine and prolactin regulated Na(+)-K(+)-ATPase activity via similar signaling pathways, including protein kinase A, protein kinase C, and phosphoinositide 3-kinase activation. The cross talk between prolactin and dopamine 1-like receptors was explained by a heterologous recruitment of dopamine 1-like receptors to the plasma membrane in renal proximal tubular cells. Prolactin had no effect on Na(+)-K(+)-ATPase activity in spontaneously hypertensive rats, a rat strain with a blunted response to dopamine. These results further emphasize the central role of the renal dopamine system in the interactive regulation of renal tubular salt balance.

Prolactin, a natriuretic hormone, interacting with the renal dopamine system.

BACKGROUND: Although prolactin affects sodium and water transport across the plasma membrane and interacts with dopamine in the brain, its role in the kidney is unclear. Here we examined the effect of prolactin and its possible interaction with the intrarenal natriuretic hormone dopamine, on proximal tubular Na(+), K(+)-ATPase activity in vitro and renal function in anesthetized rats. METHODS: Na(+), K(+)-ATPase activity was measured as ouabain-sensitive adenosine triphosphate (ATP) hydrolysis in microdissected proximal tubular segments. Renal function was studied during euvolemic conditions by conventional clearance techniques. RESULTS: Prolactin induced a dose-dependent inhibition of proximal tubular Na(+), K(+)-ATPase activity. A maximal inhibitory effect of 48% of control was observed at an in vitro prolactin concentration of 1 microg/mL. This effect was completely abolished by a dopamine D1 receptor antagonist. In tubules preincubated with inhibitors of aromatic amino acid decarboxylase (AADC), the rate-limiting enzyme in renal dopamine formation, prolactin had no effect on Na(+), K(+)-ATPase activity. In rats, prolactin infusion resulted in an increase in urinary sodium, potassium, and water excretion. These effects were also completely abolished by the D1 receptor antagonist. Prolactin had no significant effects on glomerular filtration rate (GFR) or mean arterial blood pressure. CONCLUSION: We conclude that prolactin is a natriuretic hormone which interacts with the renal dopamine system for its effects. The natriuretic response is associated with inhibition of proximal tubular Na(+), K(+)-ATPase activity.