Continual stress exposure elevates the peripheral platelet level. (A-B) Peripheral platelet counts in WT C57BL/6 mice subjected to noise stress or exhaustive exercise stress for 7 days. (C) High-pressure liquid chromatography (HPLC) analysis of plasma concentrations of NE and EPI in WT mice after stress. (D) Peripheral platelet counts in splenectomized mice exposed to continual noise or exhaustive exercise stress. (E) Peripheral platelet counts in Dbh^−/− mice after exposure to continual noise or exhaustive exercise stress. (F-G) Peripheral platelet levels in WT mice injected intraperitoneally with saline, 15 mg/kg phentolamine, or 5 mg/kg propranolol 30 minutes prior to stress exposure. (H) Peripheral platelet counts in C57BL/6J-Mpl^hlb219/J mice after exposure to noise or exhaustive exercise stress. (I) Fold induction of platelet levels on day 7 in C57BL/6J-Mpl^hlb219/J and WT mice after exposure to noise or exhaustive exercise stress. *P < .05, **P < .01, vs control; #P < .05, ##P < .01, vs stress group; ▲P < .05, ▲▲P < .01, WT vs C57BL/6J-Mpl^hlb219/J mice. Each group contains 6 to 7 mice.