Abstract:Three hours after hysterectomy the rate of urea synthesis doubles in rats. At the same time the increase in catecholamines is at a maximum, suggesting that catecholamines might be of regulatory importance. The effect of exogenous epinephrine on the rate of urea synthesis was studied in rats receiving epinephrine at rates of 2 and 20 μg/kg/h. The low dose increased plasma concentration of catecholamines two‐fold over control values (p>0.01), comparable with the increase seen after surgery, and the high dose of epinephrine increased the concentration fivefold. The high dose increased the rate of urea synthesis by 30% (p>0.05), whereas the low dose had no effect. Following a high dose of epinephrine, alanine decreased from 358 ± 29 to 254 ± 17 mmol/1 (p>0.05), indicating that the increase in urea synthesis was due to an effect on the liver rather than on extra‐hepatic tissues, in that more aminonitrogen was eliminated from plasma than released into it. In conclusion, epinephrine in physiological concentrations cannot by itself account for the increase of urea synthesis seenin vivoafter s