VASCULAR AND EXTRAVASCULAR VOLUME EXPANSION OF DOBUTAMINE AND NOREPINEPHRINE IN NORMOVOLEMIC SHEEP

In low-flow states, such as circulatory shock, both fluids and catecholamines are often coadministered. We have previously found that adrenergic agents alter volume expansion after a fluid bolus. The present study tested the volume expansion properties of dobutamine and norepinephrine in sheep treated with (series 1) and without (series 2) a fluid bolus. Series 1 (n = 6 per group): no drug (control), dobutamine (10 mu g.kg(-1).min(-1)), or norepinephrine (1.0 mu g.kg(-1).min(-1)) was begun 30 min before a 24-mL.kg(-1), 20-min, 0.9% NaCl bolus. The effect of drug and fluid on plasma volume (Delta PV), urinary output (UOP), and extravascular volume (Delta EVV) was determined. Series 2: Identical protocol but no fluid bolus. Series 1: the fluid bolus resulted in a peak and sustained Delta PV expansion. Norepinephrine (7.5 +/- 0.9 mL.kg(-1)) and dobutamine (9.5 +/- 1.1 mL.kg(-1)) significantly increased Delta PV compared with control (3.8 +/- 1.1 mL.kg(-1)). Cumulative UOP was reduced by dobutamine (3.8 +/- 1.4 mL.kg(-1)) compared with norepinephrine (25.1 +/- 3.9 mL.kg(-1)) and control (16.9 +/- 4.0 mL.kg(-1)). Norepinephrine increased Delta PV, while reducing Delta EVV after bolus. Series 2: Delta PV was unchanged in the control group. Dobutamine and norepinephrine increased Delta PV over time, 5.1 +/- 0.5 and 4.0 +/- 0.5 mL.kg(-1), respectively. At study end, UOP was lowest in dobutamine. Norepinephrine resulted in loss of Delta EVV fluid. data suggest a novel role for adrenergic receptors in regulating vascular and EVV expansion. beta-Adrenergic agonists enhance vascular volume expansion, whereas alpha-adrenergic agonists eliminate extravascular fluid.