ASSA14-03-06 Activation of D4dopamine receptor decreases AT1angiotensin II receptor expression in rat renal proximal tubule cells

Abstract

<h3>Objective</h3> The dopaminergic and renin angiotensin systems interact to regulate blood pressure. Disruption of the D₄ dopamine receptor gene in mice produces hypertension that is associated with increased renal AT₁ receptor expression. We hypothesise that the D₄ receptor can inhibit AT₁ receptor expression and function in renal proximal tubules (RPTs) cells from Wistar-Kyoto (WKY) rats but the D₄ receptor regulation of AT₁ receptor is aberrant in RPT cells from spontaneously hypertensive rats (SHRs). <h3>Methods</h3> Immortalised RPT cells from WKY and SHRs were treated by The D₄ receptor agonist, PD168077 to determine the AT₁ receptor protein expression and Na⁺-K⁺ ATPase activity, and treated by calcium channel blocker, nicardipine to determine the signalling molecule. Rats were treated <i><i>in vivo</i></i> by D₄ receptor agonist and losartan to obverse the anti-hypertensive and natriuretic effect. <h3>Results</h3> The D₄ receptor agonist, PD168077, <b><i>decreased</i></b> AT₁ receptor protein expression in a time (0–30 hrs)- and concentration (10^–9–10^–5M)-dependent manner in WKY RPT cells. By contrast, in SHR cells, PD168077 (10^–6M) <b>increased</b> AT₁ receptor protein expression. The inhibitory effect of D₄ receptor on AT₁ receptor expression in WKY RPT cells was blocked by a calcium channel blocker, nicardipine (10^–6M), or calcium-free medium, indicating that calcium is involved as a signalling molecule in the D₄ receptor-mediated signalling pathway. Angiotensin II (10^–11M) increased Na⁺-K⁺ ATPase activity in WKY cells. Pretreatment with PD168077 (10^–6M/24hrs) decreased the stimulatory effect of angiotensin II on Na⁺-K⁺ ATPase activity in WKY cells. However, in SHR cells, the inhibitory effect of D₄ receptor on angiotensin II-mediated stimulation of Na⁺-K⁺ ATPase activity was aberrant; pretreatment with D₄ receptor agonist augmented the stimulatory effect of AT₁ receptor on Na⁺-K⁺ ATPase activity in SHR cells. This was confirmed in <i><i>in vivo</i></i> studies; pre-treatment with PD128077 for one week augmented the anti-hypertensive and natriuretic effect of losartan in SHRs but not in WKY rats. <h3>Conclusions</h3> We suggest that an aberrant interaction between D₄ and AT₁ receptors may play a role in the abnormal regulation of sodium excretion and blood pressure in hypertension.