Portacaval shunt as an experimental model of impaired hepatic release of vitamin A in liver disease. Vitamin A concentrations in serum and liver were studied in rats with a portacaval shunt for 48 days after shunt surgery. In addition, serum and tissue concentrations of zinc were analyzed. Following portacaval shunting serum vitamin A concentration decreased to 25% of the level in sham-operated controls, whereas serum zinc concentration decreased to 80%. The mean urinary excretion rate of zinc increased in shunted rats [18.7 +/- 2.1 micrograms/day (0.28 +/- 0.03 mumol/day)] compared with controls [13.8 +/- 1.7 micrograms/day (0.21 +/- 0.03 mumol/day)] (P less than 0.01). The concentration of retinol and total retinoids in liver tissue increased 2-3-fold in rats with a portacaval shunt, and the ratio of retinol to retinoids was slightly increased. The differences were reduced when the total organ content was calculated, because of the reduced liver weight in the shunted rats. The concentration of zinc in liver tissue decreased in rats with portacaval shunts [30.8 +/- 4.9 micrograms/g wet wt (0.47 +/- 0.07 mumol/g) vs. 35.6 +/- 3.7 micrograms/g wet wt (0.54 +/- 0.06 mumol/g) in controls; P less than 0.01]. The concentration of zinc was inversely correlated with retinol (r = -0.52, P less than 0.05) and total retinoid levels (r = -0.70, P less than 0.05) in rats with portacaval shunts but not in controls. The data are consistent with the hypothesis of an impaired release of vitamin A from the liver in rats with portacaval shunts, an impairment that could be due to liver zinc deficiency. 