||Objectives: Stimuli that activate the sympathetic nervous system, such as acute psychological stress,
rapidly invoke a robust mobilization of lymphocytes into the circulation. Experimental animal studies
suggest that bone marrow-derived progenitor cells (PCs) also mobilize in response to sympathetic stimulation.
Here we tested the effects of acute psychological stress and brief pharmacological b-adrenergic
(bAR) stimulation on peripheral PC numbers in humans.
Methods: In two studies, we investigated PC mobilization in response to an acute speech task (n = 26) and
bAR-agonist (isoproterenol) infusion (n = 20). A subset of 8 participants also underwent the infusion
protocol with concomitant administration of the bAR-antagonist propranolol. Flow cytometry was used
to enumerate lymphocyte subsets, total progenitor cells, total haematopoietic stem cells (HSC), early HSC
(multi-lineage potential), late HSC (lineage committed), and endothelial PCs (EPCs).
Results: Both psychological stress and bAR-agonist infusion caused the expected mobilization of total
monocytes and lymphocytes and CD8+ T lymphocytes. Psychological stress also induced a modest, but
significant, increase in total PCs, HSCs, and EPC numbers in peripheral blood. However, infusion of a
bAR-agonist did not result in a significant change in circulating PCs.
Conclusion: PCs are rapidly mobilized by psychological stress via mechanisms independent of bARstimulation,
although the findings do not exclude bAR-stimulation as a possible cofactor. Considering
the clinical and physiological relevance, further research into the mechanisms involved in stress-induced
PC mobilization seems warranted.