1. The present work was carried out to compare the electroencephalographic changes in liverless rats and eviscerated rats and to determine whether substances released from the intestine, in particular ammonia, play a major part in the mechanism of hepatic encephalopathy.

2. The animals were prepared according to a three-stage procedure: ligation of inferior vena cava; 3 weeks later, end-to-side portacaval shunt; 2 days later, removal of the liver (liverless rats) or removal of the liver, spleen, stomach, intestine and pancreas (eviscerated rats).

3. In liverless rats, the electroencephalographic changes began 4–8 h after hepatectomy with a predominance of ‘slow’ sleep pattern followed by increasing changes, which consisted successively of (a) alteration of, then disappearance of, spindles of high-voltage waves; (b) predominance of slow waves; (c) depression in voltage and finally flat tracing. The mean duration of survival was 18.4 h. Mean plasma ammonia concentration 15 h after hepatectomy was 353 μmol/l.

4. In eviscerated rats, the electroencephalographic changes were similar. The mean duration of survival was 21.3 h, which is not statistically different from that of liverless rats. Mean plasma ammonia concentration 15 h after evisceration was 148 μmol/l, a value significantly lower than that of liverless rats.

5. These results suggest that ammonia, and substances released from the intestine in general, play no part or at most a minor role in the mechanism of hepatic encephalopathy of the liverless rat.

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