Abstract
BACKGROUND: Vincristine might increase circulating platelet numbers but the functional capacity of these newly released platelets is unknown. OBJECTIVE: To evaluate and compare the functionality of mature and immature (reticulated) platelets after a single intravenous dose of vincristine in dogs. ANIMALS: Ten healthy purpose-bred dogs. METHODS: Dogs prospectively received a single IV injection of 0.02 mg/kg vincristine or 0.9% saline. Before and after treatment on days 3, 5, and 7, platelets (resting and after thrombin stimulation) were assessed by flow cytometric determination of P-selectin (CD62P) expression. Reticulated platelets were distinguished using thiazole orange (TO) staining. RESULTS: Relative to saline, vincristine administration increased platelet count from day 0 to day 7 (225 ± 58 to 273 ± 65 × 10(3) /μL, vs 299 ± 76.4 to 214 ± 20 × 10(3) /μL, P = .01) and increased percentage of reticulated platelets from day 0 to day 5 (3.9 ± 1.5% to 6.1 ± 1.6%, P = .02). On all days, reticulated platelets had greater resting expression of CD62P than did mature platelets (49.6 ± 4% vs 10.2 ± 1%, P ≤ .001). Across all days, CD62P expression by reticulated platelets in the vincristine and saline-treated groups was not different when unstimulated (P = .7) or after thrombin stimulation (P = .33). CONCLUSIONS AND CLINICAL IMPORTANCE: Reticulated platelets released in response to vincristine administration function similarly to mature platelets.