Luminal nutrition is critical for maintaining normal gut function. Total parenteral nutrition (TPN) bypasses the intestine thereby causing hypoplasia of gut mucosa and pancreatic tissue eventually leading to hepatic dysfunction characterized by steatosis and cholestasis. Recent research has shown that TPN decreases oxidative pathways of metabolism in rats, but sulfation, glucuronidation and glutathione conjugation are also important biological processes and these pathways have not been evaluated. Sulfate and glucuronide conjugation control the fraction of acetaminophen converted to its toxic metabolite and glutathione conjugation controls detoxication of the acetaminophen reactive intermediate. Our preliminary studies have shown that TPN decreases the clearance of acetaminophen in adult rats, particularly formation rate of the sulfate conjugate. In the proposed studies, sulfate, glucuronide and glutathione conjugation of acetaminophen will be determined in both whole animals and in microsomes. Adult male and female rats will receive TPN and the changes in in vitro hepatic oxidative and conjugative enzyme activities, the hepatic concentrations of the cosubstrates for conjugation (PAPS, UDPGA, GSH) and hepatic energy stores (ATP) will be compared to animals receiving total enteral nutrition (TEN) or rat chow ad lib. The molecular events that control sulfation will be examined by use of cDNA probes to measure rat mRNA levels to determine the changes in transcription of sulfotransferases. Altered risks for drug-induced toxicity will be evaluated in vivo by changes in acetaminophen covalent binding studies, urinary recovery of acetaminophen mercapturate and cysteine conjugates and changes in liver transaminase enzymes. Aging severely alters human physiology and can affect drug pharmacology and toxicology 1) by causing secondary changes in the perfusion and metabolic/excretory function of eliminating organs, 2) by increasing target organ susceptibility to toxic agents and 3) by changing drug distribution to modify the usual serum drug concentration versus time pattern. In rats, age-related changes in metabolism are produced by changes in the secretion of growth hormone. Drug conjugation in aged animals will be examined to assess 1) if advanced age exaggerates the inhibition of conjugation by TPN and 2) if pretreatment of male rats with growth hormone or testosterone modifies TPN-induced inhibition of conjugation. The three long term goals of this application are l) to define the inhibition of hepatic drug conjugation by total parenteral nutrition, 2) to evaluate role of dietary alterations in composition of parenteral nutrition on this inhibition and 3) to quantify the combined effects of TPN and advanced age on drug conjugation, particularly sulfation.
