EFFECTS OF EPINEPHRINE ON UREA SYNTHESIS INVIVO IN RATS

Three hours after hysterectomy the rate of urea synthesis doubles in r ats. At the same time the increase in catecholamines is at a maximum, suggesting that catecholamines might be of regulatory importance. The effect of exogeneous epinephrine on the rate of urea synthesis was stu died in rats receiving epinephrine at rates of 2 and 20-mu-g/kg/h. The low dose increased plasma concentration of catecholamines two-fold ov er control values (p < 0.01), comparable with the increase seen after surgery, and the high dose of epinephrine increased the concentration five-fold. 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 o f epinephrine, alanine decreased from 358 +/- 29 to 254 +/- 17 mmol/l (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 m ore aminonitrogen was eliminated from plasma than released into it. In conclusion, epinephrine in physiological concentrations cannot by its elf account for the increase of urea synthesis seen in vivo after surg ery.