Background: In chronic liver disease (CLD) loss of muscle mass (sarcopenia) is highly prevalent which leads to an increased risk of hepatic encephalopathy (HE). Muscle plays a compensatory role during CLD in clearing ammonia since it expresses glutamine synthetase (GS). Therefore, diminished muscle mass in CLD leads to a further reduced capacity to clear ammonia. Male rats with CLD due to bile-duct ligation (BDL) have been shown to result in a loss of muscle in association with hyperammonemia and HE. However, these complications have not been explored in female CLD rats. Purpose: Our aim was to identify whether female sex impacts muscle mass loss, blood ammonia levels and HE in ratswith CLD. Method: Five weeks after either BDL (n=8) or Sham (n=8) surgery in male and female rats, we assessed markers of liver injury (aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase (ALP)) and function (albumin and bilirubin). Neurophenotyping was achieved using the open field test and the elevated plus maze test for anxiety, the rota-rod test for motor coordination, the novel object recognition for short-term memory and the nighttime activity test. In addition, brain edema was assessed using the gravimetric technique. Body parameters (weight, composition (MRI)) and muscle (gastrocnemius weight and circumference and grip strength) were also evaluated. In addition, muscle GS activity, ammonia clearance as well as glutamine generation (femoral venous-arterial difference)were evaluated in female vs. male BDL rats. Result(s): Female and male BDL rats had similar levels of impaired liver markers (ALP, AST, bilirubin and albumin (p<0.001)) and both developed HE (impaired motor-coordination and night activity (p<0.05)) when compared to respective Shams. However, female BDL rats did not develop brain edema and did not have loss of short-term memory. Male BDL rats experienced loss of lean mass as well as reduced muscle circumference, weight and strength (p<0.01) compared to Sham rats, while similar differences between female BDL vs. Sham rats were not found. Male and female BDL rats had comparable blood ammonia levels as well as similar muscle ammonia clearance and glutamine production. However, GS activity was lower in female vs. male BDL rats (p<0.01). Conclusion(s): Our results demonstrate that following BDL surgery, female rats develop similar degrees of CLD compared to male rats. As in male BDL rats, female rats also develop HE but female BDL rats acquire unique features (not observed in males) such as lack of brain edema and intact short-term memory. Contrary to males, female BDL rats did not develop sarcopenia compared to respective controls. However, preserved muscle mass in female BDL did not result in increased muscle ammonia clearance and glutamine production. Therefore, the similar degrees of hyperammonemia in males vs. females may be due to an upregulation in GS found in the muscle of male BDL rats. Thus, the female-induced protection against brain edema and short-term memory in BDL rats likely involves additional factors besides ammonia.
