BE-18257B

Purpose: Endothelin-1 (ET-1), a peptide produced by the vascular endothelium, causes profound renal vasoconstriction by binding to ET-A receptors. The present study examined the renal actions of ET-1 after ET-A receptors were blocked by BE-18257B to unmask the functions of ET-B receptors. Materials and methods: Renal hemodynamics and clearance measurements were obtained in anesthetized dogs after intrarenal infusion of BE-18257B at 100 ng./kg./min. (Group 1), after intrarenal infusion of ET-1 at 2 ng./kg./min. (Group 2), or after intrarenal infusion of ET-1 superimposed on BE-18257B (Group 3). Results: In Group 1, BE-18257B infusion did not alter arterial pressure, renal blood flow (RBF), GFR or tubular function. In Group 2, ET-1 infusion led to a significant decrease in RBF and GFR (37 and 40%, respectively) without altering arterial pressure. Urinary volume and sodium excretion were not changed but osmolality decreased significantly. In Group 3, BE-18257B infusion significantly attenuated the decrease in RBF caused by ET-1 and increased GFR by 40% without altering arterial pressure, associated with significant diuresis and natriuresis. Conclusion: Renal vasoconstriction caused by ET-1 is attenuated by ET-A receptor blockade with BE-18257B, which unmasks the hemodynamic and tubular actions of ET-B receptors. As a result, it limits the ET-1 induced decrease in RBF and raises GFR, and leads to a diuresis and natriuresis.

Wound contraction is an important event that minimizes the wound defect during the healing process. Involvement of insulin-like growth factor (IGF)-I and IGF-binding protein (IGFBP)-1 in wound contraction was studied using an in vitro model. Human dermal fibroblasts (1 x 10(5) cells/ml) were incorporated into a porcine type I collagen (0.21% final) in serum-free medium. The fibroblast-embedded collagen gels in a 12-well plate were floated from the well, and various reagents were then added to the assay medium. The surface area of the gel was calculated by measuring the diameters of the collagen gel. IGF-I at high doses (30 and 100 ng/ml) revealed 6.8% (P < 0.01) and 7.7% (P < 0.001) gel contraction, respectively, and des (1-3) IGF-I at 10 ng/ml produced a 4.5% gel contraction (P < 0.01). Meanwhile, IGFBP-I did not induce any significant contraction throughout the tested concentrations (0.1-100 ng/ml). A combination of IGF-I and IGFBP-1 at 1 ng/ml of each reagent, a concentration at which gel contraction was not observed when each of the reagents was tested individually, produced a 14% gel contraction (P < 0.001), whereas combinations of des (1-3) IGF-I with IGFBP-1 at the same concentrations did not promote gel contraction. The increased IGFBP-I doses in combination with 1 ng/ml IGF-I tended to enhance the gel contraction. IGF-I- and IGFBP-1-induced gel contraction was prominent during the initial 12-h incubation period. When anti-IGF-I, anti-IGFBP-1, or anti-IGF-I receptor antibody was added to the assay medium before the addition of IGF-I and IGFBP-1, the IGF-I- and IGFBP-1-induced gel contraction was significantly suppressed (P < 0.001). Endothelin-1, a vasoconstrictor peptide that is known to promote fibroblast-embedded collagen gel contraction, appeared to be partially involved in the IGF-I- and IGFBP-1-induced gel contraction, because the addition of an endothelin receptor antagonist (Bosentan or BE-18257B at 1 microg/ml) moderately suppressed the IGF-I- and IGFBP-1-induced gel contraction (P < 0.01). On the other hand, when IGF-I and IGFBP-1 were applied with endothelin-1 (1 nM), an enhanced gel contraction (29.4%) was observed that was significantly greater than that induced by either individually (P < 0.001). These results clearly indicate that the combination of IGF-I and IGFBP-1 promotes fibroblast contraction in collagen gel, and that this phenomenon is caused by IGFBP-1's strong potentiation of the IGF-I-induced gel contraction.

Background: Prior studies suggest an important role for coronary endothelium in ischemia/reperfusion (I/R) injury. Decreased endothelial release of the vasodilator nitric oxide occurs after I/R, but the role of the endothelium-derived vasoconstrictor endothelin-1 (ET-1) in I/R is unknown. Methods and results: We measured plasma ET-1 concentrations by radioimmunoassay in isolated blood-perfused neonatal lamb hearts before and after 2 hours of 10 degrees C cardioplegic ischemia and examined the effects of ET-1 and the endothelin-A (ET-A) receptor antagonist BE-18257B on the postischemic recovery of isolated hearts. ET-1 levels in coronary sinus blood before ischemia and at 0 and 30 minutes of reperfusion in 8 control hearts were constant (2.2 +/- 1.2 fmol/L, 2.2 +/- 1.3 fmol/L, and 2.5 +/- 1.0 fmol/L, respectively). In group 2 (n = 6), 10 mumol/L of BE-18257B was given just before reperfusion. In group 3 (n = 8), 10 pmol/L ET-1 was given just before the start of reperfusion. At 30 minutes of reperfusion, the ET-A antagonist hearts had significantly greater recovery of LV systolic (positive dP/dt and dP/dt at V10) and diastolic function (negative dP/dt), coronary blood flow (CBF), and MVo2 compared with controls (P < .05). The ET-1 hearts showed significantly reduced recovery of LV systolic (positive maximum and volume-normalized dP/dt) and diastolic (negative maximum dP/dt) function, CBF, and myocardial oxygen consumption compared with controls (P < .05). Conclusions: These results, combined with prior studies, suggest that I/R causes reduced production of endogenous vasodilators (eg, nitric oxide), leaving unopposed the vasoconstriction that is caused by the continued presence of ET-1. This imbalance may contribute to I/R injury. ET-A receptor antagonists may be useful therapeutic agents in reducing the injury that results from I/R.