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In this study, the involvement of osteopontin in a rat model of ischemia-induced acute renal failure (ARF) was evaluated. In unilaterally nephrectomized Sprague Dawley rats where the left artery was occluded for 30 min., plasma creatinine levels increased significantly within two hours following reperfusion indicating the onset of renal failure. Northern analysis of kidney cortical RNA from these rats showed a time-dependent increase in osteopontin mRNA expression that was significantly higher than sham-operated rats. Since endothelin-1 (ET-1) is implicated as a mediator of acute renal failure, we evaluated its effects on osteopontin expression in a rat mesangial cell-line. Data from in vitro studies indicated that endothelin-1 (ET-1) caused a modest but reproducible increase in osteopontin mRNA in these cells. While the signal for osteopontin upregulation in the rat model is not known, ET-1, which is known to be increased during ischemia, may contribute at least in part to this process., (Copyright 1997 Academic Press.)

Using canine spleen and lung membranes as model systems, we have shown the presence of subtypes of ETB receptors. This classification was done based on the binding profiles of various analogs of ET-1 that have been identified as ETB-selective. Saturation binding experiments performed with [125I] ET-3 and [125I] IRL-1260 (ETB-selective ligands) indicated that [125I] IRL-1620 labeled 80-90% of [125I] ET-3 binding sites in canine lung, whereas in canine spleen, the binding of [125I] IRL-1620 was 10-20% of [125I] ET-3 binding. In addition, competition binding experiments using ETB-selective agonists [Ala1,3,11,15]-ET-1 (also known as 4-Ala ET-1), N-acetyl-[Ala11,15] ET-1 (6-21) also known as BQ3020 and Suc-[Glu9, Ala11,15] ET-1 (8-21) also known as IRL-1620 indicated that all three ligands displaced [125I] ET-3 from canine lung membranes with approximately 500-1000 fold greater affinity than canine spleen membranes. On the other hand, ET-1, ET-3, S6a, S6b, and S6d displayed very similar IC50 values in both preparations, except S6c which was approximately 20 fold less potent in canine spleen compared to lung. These data indicate that ETB receptors present in canine spleen are different from those present in lung and that ETB-selective linear as well as truncated analogs of ET-1 are good tools to identify these subtypes of ETB receptors.

Experiments were designed to compare the distribution and physiological roles of endothelin (ET) receptor subtypes, ETA and ETB, in the kidneys of normotensive Sprague-Dawley (SD) and spontaneously hypertensive (SH) rats. Using [125I] ET-1 and subtype-selective ligands sarafotoxin 6c (S6c, ETB-selective agonist) and BQ123 (ETA-selective antagonist), the distribution of ETA and ETB receptors in SD rat kidney cortex, outer medulla and papilla was calculated to be 50:50, 30:70 and 10:90, respectively. The ET receptor subtypes in outer medulla and papilla of age-matched SH rats were similar to those of SD. However, in the cortex of SH rats, the ratio of ETA to ETB was 25:75 compared to 50:50 in SD rats. In addition, the affinity of the ET receptors was also higher in SH rats (117 pM vs. 235 pM). In the conscious SD rats, bolus i.v. injections of ET-1 and S6c elicited similar dose-dependent decrease in renal blood flow (RBF), which were unaffected by the infusion of the selective ETA receptor antagonist, BQ123. The SH rats were more sensitive to the renal vasoconstrictor effect of S6c and ET-1. Also, the dose-response curve to S6c was shifted to the left when compared to ET-1; however, BQ123 infusion abolished this difference. In renal clearance studies, BQ123 infusions decreased RBF and glomerular filtration rate (GFR) only in SH rats, and the fractional excretion of sodium only in SD rats. The combined data indicate that the distribution and functional roles of ETA and ETB receptor subtypes are altered in the kidneys of SH rats.