INFLUENCE OF ALPHA-ADRENERGIC RECEPTOR STIMULATION ON SPLANCHNIC INTRAVASCULAR VOLUME IN CONSCIOUS HUMANS

The influence of selective alpha-adrenergic receptor stimulation on total splanchnic intravascular volume and blood volume in individual splanchnic organs in humans has not been previously examined. The present study employed a previously validated quantitative radionuclide imaging technique, involving a gamma camera and Tc-99m labeled erythrocytes, to measure changes in total splanchnic, hepatic, splenic, and extrahepatosplenic volume during a 20-minute phenylephrine infusion (30-120-mu-g min-1 iv). Changes in total splanchnic volume were estimated from changes in total splanchnic radioactivity, blood radioactivity, and estimated in vivo tissue attenuation. Radionuclide-estimated total splanchnic volume increased 477 +/- 96 ml (P < 0.0003) at the end of phenylephrine infusion. Hepatic volume increased 25 +/- 5% (P < 0.0003), splenic volume decreased 46 +/- 7% (P < 0.0003), and extrahepatosplenic volume decreased 15 +/- 2% (P < 0.0003). Systolic and diastolic arterial pressures increased from 119 +/- 4 to 138 +/- 5 mmHg (P < 0.0003) and from 83 +/- 1 to 96 +/- 2 mmHg (P < 0.0003), respectively. Heart rate decreased from 62 +/- 2 to 51 +/- 3 bpm (P < 0.0003). Thus, in man, selective alpha-adrenergic receptor stimulation is associated with an increase in splanchnic intravascular volume that is due to an increase in hepatic volume and occurs despite decreases in splenic and extrahepatosplenic volumes. This increase in total splanchnic volume would be associated with a decrease in venous return from the splanchnic vasculature to the right heart which would act to decrease cardiac output.