Modulation of murine hemopoiesis in vivo by a synthetic hemoregulatory pentapeptide (HP 5b)

A synthetic pentapeptide analogous to an inhibitory factor associated with human granulocytes was tested in vivo on female C3H mice. The relative and absolute numbers of myelopoietic and erythropoietic cells in the bone marrow were measured following injections as well as the continuous infusion of the pentapeptide in dose ranges between 10(-8)M and 10(-4)M (0.12 micrograms to 1.2 mg/mouse). In low doses, the pentapeptide reduced the number of myelopoietic cells in the bone marrow, and this was accompanied by reduced numbers of granulocytes and monocytes and peripheral blood. Elevated doses also decreased erythropoiesis. In contrast, continuous infusion of 14 micrograms/h for 19 days seemed to make the myelopoietic cells refractory to further action. A regulatory function of the pentapeptide is proposed.