High intestinal sodium absorption is one mechanism of hypertension and constipation. The sodium-proton-exchanger subtype 3 (NHE3) is an important mediator of sodium absorption in the gut. SAR218034 (SAR) is an orally nonabsorbable specific NHE3 inhibitor. The effect of SAR (1 mg/kg per day in chow) on feces sodium excretion, systolic blood pressure via tail cuff, and gene expression of NHE3 in the gut were studied in senescent lean hypertensive rats (spontaneously hypertensive rats-lean, loaded with NaCl 0.7% in drinking water) and in hypertensive, obese, and hyperinsulinemic rats (spontaneously hypertensive rats-obese, not loaded with NaCl). In spontaneously hypertensive rats-lean, inhibition of intestinal NHE3 by SAR increased feces sodium excretion and reduced urinary sodium excretion, whereas absolute sodium balance and serum sodium concentration were not changed. This suggests reduced intestinal sodium absorption in SAR-treated animals and was associated with increased feces water content (58% versus 42% in placebo treated animals; P=0.0001) and reduction in systolic blood pressure from 222 ± 7 to 198 ± 2 mm Hg (P=0.0001). Angiotensin-converting enzyme inhibition by ramipril plus NHE3 inhibition resulted in an additive blood pressure-lowering effect. In spontaneously hypertensive rats-obese, SAR lowered systolic blood pressure but did not modify serum insulin or cholesterol levels. Gene expression of NHE3 was upregulated in the ileum and colon but not in the jejunum of SAR-treated rats. Reduction of intestinal sodium absorption by selective NHE3 inhibition in the gut reduces high blood pressure and increases feces water excretion. Intestinal NHE3 blockade could be a new treatment strategy for elderly patients suffering from high blood pressure and constipation.

The substrate specificity of the ileal and the hepatic Na ؉ /bile acid cotransporters was determined using brush border membrane vesicles and CHO cell lines permanently expressing the Na ؉ /bile acid cotransporters from rabbit ileum or rabbit liver. The hepatic transporter showed a remarkably broad specificity for interaction with cholephilic compounds in contrast to the ileal system. The anion transport inhibitor diisothiocyanostilbene disulfonate (DIDS) is a strong inhibitor of the hepatic Na ؉ /bile acid cotransporter, but does not show any affinity to its ileal counterpart. Inhibition studies and uptake measurements with about 40 different bile acid analogues differing in the number, position, and stereochemistry of the hydroxyl groups at the steroid nucleus resulted in clear structure-activity relationships for the ileal and hepatic bile acid transporters. The affinity to the ileal and hepatic Na ؉ /bile acid cotransport systems and the uptake rates by cell lines expressing those transporters as well as rabbit ileal brush border membrane vesicles is primarily determined by the substituents on the steroid nucleus. Two hydroxy groups at position 3, 7, or 12 are optimal whereas the presence of three hydroxy groups decreased affinity. Vicinal hydroxy groups at positions 6 and 7 or a shift of the 7-hydroxy group to the 6-position significantly decreased the affinity to the ileal transporter in contrast to the hepatic system. 6-Hydroxylated bile acid derivatives are preferred substrates of the hepatic Na ؉ /bile acid cotransporter. Surprisingly, the 3 ␣ -hydroxy group being present in all natural bile acids is not essential for high affinity interaction with the ileal and the hepatic bile acid transporter. The 3 ␣ -hydroxy group seems to be necessary for optimal transport of a bile acid across the hepatocyte canalicular membrane. A modification of bile acids at the 3-position therefore conserves the bile acid character thus determining the 3-position of bile acids as the ideal position for drug targeting strategies using bile acid transport pathways.

To identify protein components of the intestinal cholesterol transporter, rabbit small intestinal brush border membrane vesicles were submitted to photoaffinity labeling using photoreactive derivatives of 2-azetidinone cholesterol absorption inhibitors. An integral membrane protein of M r 145.3 þ 7.5 kDa was specifically labeled in brush border membrane vesicles from rabbit jejunum and ileum. Its labeling was concentrationdependently inhibited by the presence of cholesterol absorption inhibitors whereas bile acids, D-glucose, fatty acids or cephalexin had no effect. The inhibitory potency of 2-azetidinones to inhibit photolabeling of the 145 kDa protein correlated with their in vivo activity to inhibit intestinal cholesterol absorption. These results suggest that an integral membrane protein of M r 145 kDa is (a component of) the cholesterol absorption system in the brush border membrane of small intestinal enterocytes. ß

AVE2268, a substituted glycopyranoside, is an orally active and selective inhibitor of sodium-dependent glucose transporter 2 (SGLT2; IC50 = 13 nmol/L). Investigation of the pharmacological profile of AVE2268 on urinary glucose excretion (UGE) and blood glucose after glucose challenge (po or Intraperitoneal) was performed in mice and rats. AVE2268 caused a dose-dependent increase of UGE in mice (ID30 = 79 +/- 8.1 mg/kg p.o.) and rats (ID30 = 39.8 +/- 4.0 mg/kg p.o.). AVE2268 in mice was more potent to decrease blood glucose ascent when glucose was given intraperitoneally (ID50 = 13.2 +/- 3.9 mg/ kg), compared to orally administered glucose (ID50 = 26.1 +/- 3.9 mg/kg), showing that AVE2268 has no effects on SGLT 1 in the gut in vivo, which is in accordance with ist very low affinity to the SGLT 1 in vitro (IC50 >10,000 nmol/L). During an oral glucose tolerance test, AVE2268 dose-dependently increased UGE, with subsequent decreases of AUC and blood glucose. A highly significant inverse correlation between AUC and UGE was found (p < 0.001). The increase in UGE is linked to the inhibition of SGLT2 only. This profile renders AVE2268 as a new antidiabetic drug for the treatment of type 2 diabetes.

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