Fig. 2. Number of circulating polymorphonuclear cells (PMN) and opioid peptide content after granulocyte colony-stimulating factor (G-CSF) stem cell factor (SCF) treatment. (A ) Rats (n = 6) were subcutaneously injected with solvent (control; black bar ) or with G-CSF+SCF (white bar ) for 5 days. Immune cell subpopulations of circulating blood were quantified by flow cytometry. Circulating PMN were significantly increased (*P < 0.05, Mann–Whitney test). (B ) In isolated PMN of rats treated with G-CSF+SCF, β-endorphin (END) content measured by radioimmunoassay was significantly decreased (***P < 0.001), whereas Met-enkephalin (ENK) content was unchanged (P > 0.05 [not significant (n.s.)], n = 9 or 10, both t  test).