EPINEPHRINE INFUSION IN SHEEP - SYSTEMIC AND RENAL HEMODYNAMIC-EFFECTS

Objective: To evaluate the dose-response effects of graded epinephrine infusions on systemic and renal hemodynamics. Design: Prospective, do se-response study. Setting: Laboratory at a university hospital. Subje cts: Thirteen conscious, chronically catheterized, adult merino sheep. Interventions: Ten sheep received five infusions of epinephrine (5, 1 0, 20, and 40 mu g/min; the 40-mu g/min dose was repeated) and a place bo (saline) on separate days (at least 1 day apart). Each drug infusio n was administered for 4 hrs on separate days after a 90-min baseline was established. Plasma catecholamine values and renin activity were m easured in an additional three sheep infused with 40 mu g/min epinephr ine. Measurements and Main Results: Renal blood flow was measured, usi ng an electromagnetic flow transducer; these data, along with aortic a nd pulmonary arterial pressure, were continuously recorded after analo g-to-digital conversion. Cardiac output was intermittently measured by thermodilution. Epinephrine resulted in a dose-dependent increase in mean arterial pressure (p <.001), and in cardiac output at 30, 60, and 120 mins after the start of the infusion. Concurrently, systemic vasc ular resistance was initially depressed below baseline, but then gradu ally increased during the 4-hr infusion period. Although a dose-depend ent increase in renal vascular resistance was found, 5- and 10-mu g/mi n of epinephrine failed to alter renal vascular resistance. However, 2 0- and 40-mu g/min of epinephrine increased renal vascular resistance by 77% and 94% respectively, at 10 mins, but these values decreased to 17% and 16% of baseline by 120 mim. Consequently, an early dose-depen dent decrease in renal blood flow was also time dependent, with renal blood flow increasing back to or above baseline at all studied infusio n rates of epinephrine. Conclusions: Using a clinically relevant dose regimen, epinephrine increased mean arterial pressure and cardiac outp ut. Penal blood flow decreased transiently, but returned to baseline w ithin 30 to 60 mins.