Male Sprague-Dawley rats weighing 300 to 350 g were used. End-to-side portacaval shunts were constructed according to the technique of Lee and Fisher.13 Eight days after the operation, a Silastic catheter for infusions was positioned in the external jugular vein and was protected by a flexible metal sheath attached to a swivel. Animals were anesthetized with diethyl ether for all surgical procedures.
Two separate experiments were performed.
In the first experiment, 11 rats were infused with a solution containing 0.4 mole/L of NH4+ salts (200 mmole/L of NH4+ acetate and 200 mmole/L of NH4+ bicarbonate; pH, 7.4) and 11 rats were infused with 0.4 mole/L of NH4+ salts and 0.3 mole/L of BCAAs (0.1 mole/L each of leucine, isoleucine, and valine; final pH, 7.4). The rate of infusion was 0.9 mL/100 g of body weight per hour. The infusion was continued until the rat