Gastrin and D1 dopamine receptor interact to induce natriuresis and diuresis

Abstract

Oral NaCl produces a greater natriuresis and diuresis than the intravenous infusion of the same amount of NaCl. Gastrin is the major gastrointestinal hormone taken up by renal proximal tubule (RPT) cells. We hypothesized that renal gastrin and dopamine receptors interact to synergistically increase sodium excretion, an impaired interaction of which may be involved in the pathogenesis of hypertension. In Wistar-Kyoto rats, infusion of gastrin induced natriuresis and diuresis, which was abrogated in the presence of a gastrin (cholecystokinin B receptor [CCKBR]; CI-988) or a D1-like receptor antagonist (SCH23390). Similarly, the natriuretic and diuretic effects of fenoldopam, a D1-like receptor agonist, were blocked by SCH23390, as well as by CI-988. However, the natriuretic effects of gastrin and fenoldopam were not observed in spontaneously hypertensive rats. The gastrin/D1-like receptor interaction was also confirmed in RPT cells. In RPT cells from Wistar-Kyoto but not spontaneously hypertensive rats, stimulation of either D1-like receptor or gastrin receptor inhibited Na(+)-K(+)-ATPase activity, an effect that was blocked in the presence of SCH23390 or CI-988. In RPT cells from Wistar-Kyoto and spontaneously hypertensive rats, CCKBR and D1 receptor coimmunoprecipitated, which was increased after stimulation of either D1 receptor or CCKBR in RPT cells from Wistar-Kyoto rats; stimulation of one receptor increased the RPT cell membrane expression of the other receptor, effects that were not observed in spontaneously hypertensive rats. These data suggest that there is a synergism between CCKBR and D1-like receptors to increase sodium excretion. An aberrant interaction between the renal CCK BR and D1-like receptors (eg, D1 receptor) may play a role in the pathogenesis of hypertension.

Keywords: hypertension; kidney; kidney tubules, proximal; receptor, cholecystokinin B; receptors, dopamine D1.

Figure 1. Effect of the renal infusion of gastrin on urine flow and sodium excretion in WKY and SHRs

(A) Urine flow (V); (B) Absolute sodium excretion (U_NaV). Varying dosages of gastrin (0.1–5.0 µg/kg/min) were infused into the right suprarenal artery of anesthetized rats. *P<0.05 vs. control, (repeated measures ANOVA, Holm-Sidak test). ^#P<0.05 vs. SHR, n= 6 (t-test).

Figure 2. Effect of the renal infusion of a D₁-like receptor agonist, fenoldopam, on urine flow and sodium excretion in WKY rats

(A) Urine flow (V); (B) Absolute sodium excretion (U_NaV). Varying dosages of the D₁-like receptor agonist, fenoldopam (0.1–5.0 µg/kg/min), were infused into the right suprarenal artery of anesthetized rats. *P<0.05 vs. control, n= 4 (Repeated measures ANOVA, Holm-Sidak test).

Figure 3. Interaction between gastrin and D₁-like receptors on urine flow and sodium excretion in WKY rats

A and B: The gastrin-mediated diuresis and natriuresis were blocked by a D₁-like receptor antagonist (SCH23390) in WKY rats. Effect of gastrin (1.0 µg/kg/min; n=5), gastrin receptor antagonist CI-988 (1.0 mg/kg/min; n=5), D₁-like receptor antagonist SCH23390 (0.4 µg/kg/min; n=5), or in combination (gastrin+SCH23390, n=5; gastrin+CI-988, n=6) on urine flow (V) (A) and absolute sodium excretion (U_NaV) (B). During the control period, only the vehicle (saline) was infused. During period 1 (P1), the vehicle (saline) was infused in the gastrin group; CI-988 was infused in vehicle+CI-988, gastrin+CI-988; SCH23390 was infused in the vehicle+SCH23390 and gastrin+SCH23390 groups. During periods 2–3 (P2, P3), gastrin, instead of vehicle, was infused in the gastrin+SCH23390 and gastrin+CI-988 groups. In the recovery period, only the vehicle (saline) was infused in all the groups. Data are expressed as mean±SEM. *P<0.05 vs. other groups (Factorial ANOVA, Holm-Sidak test). C and D: The fenoldopam-mediated diuresis and natriuresis were blocked by gastrin receptor antagonist (CI-988) in WKY rats. Effect of the D₁-like receptor agonist fenoldopam (1.0 µg/kg/min; n=5), D₁-like receptor antagonist SCH23390 (0.4 µg/kg/min; n=5), or in combination (fenoldopam+CI-988, n= 6; fenoldopam+SCH23390, n=5) on urine flow (V) (C) and absolute sodium excretion (U_NaV) (D). During the control period, only the vehicle (saline) was infused. During period 1 (P1), the vehicle (saline) was infused in the fenoldopam group; CI-988 was infused in the vehicle+CI-988 and fenoldopam+CI-988; SCH23390 was infused in vehicle+SCH23390 and fenoldopam+SCH23390 groups. During periods 2–3 (P2, P3), fenoldopam, instead of vehicle, was infused in the fenoldopam+SCH23390 and fenoldopam+CI-988 groups. In the recovery period, only the vehicle (saline) was infused in all the groups. Data are expressed as mean±SEM. *P<0.05 vs. other groups (Factorial ANOVA, Holm-Sidak test).

Figure 4. Co-localization of CCK_BR and D₁R in WKY RPT cells

Co-localization appears as yellow after merging the images of FITC-tagged D₁R (green) and TRITC-tagged CCK_BR (red). No staining is seen without the antibodies (DIC). DIC: differential interference contrast.

Figure 5. Effect of gastrin or fenoldopam on the co-immunoprecipitation of CCK_BR and D₁R in RPT cells from WKY and SHRs

The cells were incubated with gastrin (10⁻⁹ M, A) or fenoldopam (10⁻⁷ M, B) for 15 min. Thereafter, the samples were immunoprecipitated with CCK_BR antibodies and immunoblotted with D₁R antibodies (* P<0.05 vs. control; n=3–5; factorial ANOVA, Holm-Sidak test). One immunoblot (74 kDa) is depicted in the inset: (lane 1= vehicle-treated RPT cells from WKY rats, lane 2= gastrin-treated RPT cells from WKY rats, lane 3= vehicle-treated RPT cells from SHRs, and lane 4= gastrin-treated RPT cells from SHRs).