Influence of α‐adrenergic receptor stimulation on splanchnic intravascular volume in conscious humans

Abstract

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 micrograms 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 less than 0.0003) at the end of phenylephrine infusion. Hepatic volume increased 25 +/- 5% (P less than 0.0003), splenic volume decreased 46 +/- 7% (P less than 0.0003), and extrahepatosplenic volume decreased 15 +/- 2% (P less than 0.0003). Systolic and diastolic arterial pressures increased from 119 +/- 4 to 138 +/- 5 mmHg (P less than 0.0003) and from 83 +/- 1 to 96 +/- 2 mmHg (P less than 0.0003), respectively. Heart rate decreased from 62 +/- 2 to 51 +/- 3 bpm (P less than 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.

Human cardiovascular dose–response to supplemental oxygen

“…Sympathetic receptor stimulation may decrease venous return but the results are conflicting (Leenen et al 1988, Butterworth et al 2004. Our results, however, indicate pooling of arterial or venous blood, which normally occurs in the capacitance vessels or in the larger veins (Guyton 1996), but for example the splanchnic vasculature may also be involved (Bell et al 1991). In the lung, hypoxic constriction is described (Dantzker et al 1974), but not the contrary.…”

“…2004). Our results, however, indicate pooling of arterial or venous blood, which normally occurs in the capacitance vessels or in the larger veins (Guyton 1996), but for example the splanchnic vasculature may also be involved (Bell et al. 1991).…”

Uneven Changes In Circulating Blood Cell Counts With Adrenergic Stimulation To The Canine Spleen

“…1,10 Blue and Weiss 11 have described that concentrated red cells are stored in both sinuses and the reticular meshwork of red pulp of the dog spleen and are expelled into the systemic circulation by contractions of trabecular and capsular smooth muscles and probably of the reticular meshwork. Several in vivo assessments in the normal human spleen have demonstrated reductions in splenic capacity of 52 and 46% during adrenoceptor stimulation with noradrenaline 12 and phenylephrine 13 and 46 and 34% during exercise. 14,15 These findings suggest that the human spleen is also capable of mobilizing stored blood to some extent during ␣-adrenoceptor stimulation.…”

Assessment of the human splanchnic venous volume-pressure relation using radionuclide plethysmography. Effect of nitroglycerin.

“…No significant differences were noted between the control (C) splanchnic vascular V-P curve (average of control 1 and control 2 data) and those recorded 2-6 minutes (PLB-1), 9-13 minutes (PLB-2), and 20-24 minutes (PLB-3) after sublingual administration of PLB (p>0. 52 The few studies of the human splanchnic veinS5-7, 25,28,33,36,37 have assessed changes in SVV during acute interventions, but venous V-P relations have never been defined.…”