Su1684 Adenosine Regulates Cholangiocyte IL-6 Secretion via the A2B Receptor

Abstract

Background. Although the kidney is believed to play a minor role in bile acid (BA) excretion, chronic renal failure (CRF) has been reported to be associated with increased serum bile acid levels and alterations in BA homeostasis. According to a recent report, rats studied 3 weeks after 5/6 nephrectomy and fed a high-protein diet exhibited increased activities of hepatic HMG-CoA reductase (HMG-CoAR) and cholesterol 7 alpha-hydroxylase (Cyp7a1), despite normal corresponding mRNA levels. Design and Methods. This study was designed to examine the effects of naturally progressing CRF of longer duration on the hepatic and renal mRNA and protein levels of the bile acid synthesizing enzyme Cyp7a1 and the bile acid transporters, Ntcp, Bsep, Mrp3, Ost-alpha and OST-beta. Sprague-Dawley rats were randomized to the CRF group (5/6 nephrectomy) or to the sham-operated, placebo-treated normal control group. They were allowed free access to regular rat chow and were analyzed 8 weeks after surgery. Results obtained in CRF rats were compared to those obtained in rats that had undergone uninephrectomy (UNX). Results. The CRF group exhibited significantly increased plasma cholesterol and bile acid concentrations. Hepatic Cyp7a1 mRNA, and protein levels were almost identical in the two groups. Hepatic Mrp3, Ostα and Ost-β expression was increased at both the mRNA and protein levels, suggesting increased basolateral efflux of bile acids into basolateral blood. However, no such changes in bile acid transporter expression were observed in kidney. In UNX rats, similar changes in plasma bile acid levels and in the expression of bile acid transporters were found. We hypothesize, that the increase in plasma bile acids is an early event in the progression of CRF and is caused by increased efflux across the basolateral hepatocyte membrane.