Aging and Marrow Neutrophil Reserves

Objectives: Measurement of blood neutrophil (PMN) counts after the administration of hydrocortisone, granulocyte colony-stimulating factor (G-CSF) and epinephrine.

Design: Prospective study, with subjects serving as their own controls before and after administration of hydrocortisone, G-CSF, and epinephrine.

Setting: The G-CSF and hydrocortisone studies were conducted at the Clinical Research Center, University of Washington, and the epinephrine study was conducted at the Seattle VA Medical Center.

Participants: Healthy volunteers of both sexes (ages 20 to 30 years and 70 to 80 years) were recruited from the community. The subjects had no acute or chronic medical problems and were on no prescription medications.

Main Outcome Measures: Change in the blood PMN count after administration of hydrocortisone (25 and 200 mg intravenously), G-CSF (30 and 300 micrograms subcutaneously), or epinephrine (10, 25, and 50 ng/kg/min intravenously).

Results: Baseline PMN counts were similar for all comparison groups. The peak PMN response (maximum count-baseline count) to hydrocortisone was significantly less in the older subjects (P < 0.01) at both doses. The peak PMN responses were 4588 +/- 418/mm3 (25 mg) and 6906 +/- 1121/mm3 (200 mg) in the young and 1886 +/- 399/mm3 (25 mg) and 2387 +/- 372/mm3 (200 mg) in the elderly subjects. The peak PMN response following G-CSF was not different (P > 0.05) in the two groups at both the dosages: 6696 +/- 736/mm3 (30 micrograms) and 9801 +/- 893/mm3 (300 micrograms) in the young and 6340 +/- 833/mm3 (30 micrograms) and 9733 +/- 956/mm3 (300 micrograms) in the elderly. There was no age-related change in the response to epinephrine.

Conclusions: Aging has no effect on baseline PMN counts, bone marrow PMN reserves as measured with G-CSF, and blood PMN pools as measured with epinephrine. However the ability to mobilize these PMNs from the marrow into blood, as measured by the hydrocortisone response, is significantly reduced in the elderly.