Plasma renin activity during controlled hemorrhage in the dog.

Purebred 1-year-old Beagles were made hypotensive by controlled hemorrhage (3 ml/kg-1/min-1). Femoral artery blood samples were collected every 5 minutes during controlled hemorrhage, until the blood pressure decreased to 30+/-5 mm Hg. Samples were then collected every 10 minutes for 40 minutes. Blood was not reinfused during the procedure. Carotid blood pressure, electrocardiogram lead II, and respiration rate were recorded. The results of the radioimmunoassay for renin activity indicated that arterial plasma renin activity formed a bimodal activity curve. Plasma renin activity did not reach any plateau, and it continued to increase throughout the experiment. Decreasing blood pressure and heart rate statistically showed a relationship with plasma renin activity (P less than 0.001). There was no interaction between pressure and heart rate; both were strong and independent. Female dogs had a higher plasma renin activity than did male dogs (P less than 0.001) throughout the experimental period. Plasma renin activity remained above resting activity throughout the development of hemorrhagic shock.