Dynamic expression of the angiotensin II type 2 receptor and duodenal mucosal alkaline secretion in the Sprague-Dawley rat

Activation of angiotensin II type 2 receptors (AT2R) has been shown to stimulate duodenal mucosal alkaline secretion (DMAS) in Sprague-Dawley rats (S-D). This finding could not be confirmed in another line of S-D, and the present study investigates whether the level of AT2R expression determines the response to the AT2R agonist CGP42112A. DMAS was measured in anaesthetized rats using in situ pH-stat titration. Real-time PCR and Western blot were used to assess AT1R and AT2R RNA and protein expression, respectively. CGP42112A (0.1 mu g kg(-1)min(-1)<smallcapitals>i.v.</smallcapitals>) elicited a 45% net increase in DMAS in the previous S-D line studied, whereas no change occurred in the new S-D line. Luminal administration of prostaglandin E-2 (10(-5)<smallcapitals>m</smallcapitals>) increased DMAS similarly in both S-D lines. AT2R protein expression was significantly higher in tissue from the previous line compared to the new line. Individual AT1R to AT2R ratios (RNA and protein) were significantly higher in the new line compared to the previous S-D line. In the new S-D line intravenous infusion of angiotensin II (Ang II; 10 mu g kg(-1) h(-1)) over 120 min significantly lowered the duodenal AT1aR to AT2R RNA ratio. Prolonged Ang II infusion over 240 min increased AT2R protein expression and evoked a 42% stimulatory response in DMAS to CGP42112A. The level of local AT2R expression determines the effect of the AT2R agonist CGP42112A on rat duodenal mucosal alkaline secretion. AT2R expression should be confirmed before interpreting the experimental effects of pharmacological interferences with this receptor.