The effect of cyclosporin A on the hepatic energy status and intracellular pH of the liver and its response to a fructose challenge has been investigated using in vivo phosphorus-31 nuclear magnetic resonance spectroscopy in dogs. Three experimental groups were studied: (a) control dogs (n = 5), (b) dogs 4 days after the creation of an end-to-side portacaval shunt (n = 5), and (c) dogs 4 days after portacaval shunt and continuous infusion of cyclosporin A (4 mg/kg/day) by way of the left portal vein (portacaval shunt plus cyclosporin A, n = 5). The phosphorus-31 nuclear magnetic resonance spectra were obtained at 81 MHz using a Bruker BIOSPEC II 4.7-tesla nuclear magnetic resonance system equipped with a 40-cm horizontal bore superconducting solenoid. The phosphomonoesters (p < 0.01), inorganic phosphate and ATP levels (p < 0.05) were decreased significantly in portacaval shunt-treated and in portacaval shunt-plus-cyclosporin A-treated dogs compared with unshunted control dogs. After a fructose challenge (750 mg/kg body wt, intravenously), fructose-1-phosphate metabolism was reduced in portacaval shunt-treated dogs compared with either the normal or portacaval shunt-plus-cyclosporin A-treated dogs (p < 0.05). Both portacaval shunt-and portacaval shunt-plus-cyclosporin A-treated dogs demonstrated a reduced decline in ATP levels after fructose infusion when compared with the controls (p < 0.05). Immediately after the fructose challenge, the intracellular pH decreased from 7.30 ± 0.03 to 7.00 ± 0.05 in all animals (p < 0.01) and then gradually returned to normal over 60 min. These data, obtained in vivo using phosphorus-31 nuclear magnetic resonance spectroscopy of the liver after a portacaval shunt, suggest that: (a) the energy status of the liver is reduced in dogs with a portacaval shunt compared with that of normal controls and (b) cyclosporin A treatment ameliorates the reduction in hepatic metabolism normally observed after a fructose challenge to the liver with a portacaval shunt. In this study, the dog with portacaval shunt (PCS) (Eck's fistula) was used. PCS usually is associated with hepatic atrophy and low-grade hepatocyte hyperplasia (16)(17)(18)(19)(20)(21). We have previously shown in this model that CsA prevents the atrophy and augments the hyperplasia (21). In this report, the effect of CsA treatment on the metabolic events caused by PCS is examined in vivo using phosphorus-31 nuclear magnetic resonance ( 31 P-NMR) spectroscopy.Various in vivo studies using 31 P-NMR spectroscopy (22-24) have reported on the intracellular pH (pH i ), the hepatic content of ATP, sugar phosphates and inorganic phosphate (Pi) under basal conditions and after a physiological challenge with fructose. The only other NMR study relevant to hepatic regeneration or hepatocyte growth control was performed in vitro and used perchloric-acid extracts of tissue samples to calculate phosphate metabolites (25). Materials and Methods Experimental DesignFifteen female purebred Beagle dogs weighing between 8.5 kg and 15 kg were ...