Platelet number and function in response to a single intravenous dose of vincristine.

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 /μL, vs 299 ± 76.4 to 214 ± 20 × 10 /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.